Glomerulas arachidonate lipoxygenation in rat nephrotoxic serum nephritis

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Functional significance of renal prostacyclin and thromboxane A₂ production in patients with systemic lupus erythematosus

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Myocardial reperfusion: a double-edged sword?

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E Braunwald, R A Kloner

Stereoselective renal clearance of pindolol in humans.

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In this study, pindolol, a beta-adrenoceptor blocking agent marketed as a racemic mixture, was used as a model compound to investigate stereoselective renal clearance of organic cations in human beings. Six normal subjects received an oral dose of 20 mg racemic pindolol. Heart rate and blood pressure were measured throughout the study. A stereospecific high performance liquid chromatographic procedure was used to quantitate the concentrations of d- and l-pindolol in plasma and urine. Renal clearance and other pharmacokinetic parameters of both enantiomers were calculated and compared. The renal clearance of l-pindolol was greater than that of d-pindolol in all subjects. The renal clearance (mean +/- SD) was 240 +/- 55 ml/min for l-pindolol and 200 +/- 51 ml/min for d-pindolol (P less than 0.01). Since stereoselective binding to plasma proteins was not observed, differences in renal clearance between d- and l-pindolol were caused by either stereoselective renal transport, or stereoselective renal metabolism. The area under the plasma concentration-time curve, the amount of drug excreted, and the half-life of l-pindolol were greater than those of d-pindolol, which suggests that pindolol was also eliminated stereoselectively by nonrenal routes. The slopes of the resting heart rate vs. the plasma concentration of l-pindolol were significantly less than zero and were significantly correlated to the pretreatment heart rate, which supports the hypothesis that intrinsic sympathetic tone largely determines the effect of pindolol on the resting heart rate. The observation that pindolol is eliminated stereoselectively by the kidney may have clinical implications for other racemic drugs that are renally eliminated.

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P H Hsyu, K M Giacomini

Effects of bile and bile salts on growth and membrane lipid uptake by Giardia lamblia. Possible implications for pathogenesis of intestinal disease.

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We have shown previously that ox and pig bile accelerate in vitro growth of Giardia lamblia. We have now investigated the possible mechanisms by which mammalian biles promote parasite growth. Growth effects of (a) ox, pig, guinea pig, and human biles, (b) pure bile salts, and (c) egg and soybean lecithins were studied in the presence of a lecithin-containing growth medium. Individually, dilute native bile and pure sodium taurocholate (TC), glycocholate (GC), and taurodeoxycholate (TDC) promoted parasite growth; growth was most marked with biles of high phospholipid content, with biles enriched in more hydrophobic bile salts (ox approximately equal to human greater than pig greater than guinea pig) and with micellar concentrations of GC and submicellar concentrations of TC and TDC. By measuring uptake of radiolabeled biliary lipids from bile and bile salt-supplemented growth medium, we showed that the parasite consumed bile lipids, with the rank order lecithin greater than bile salts. Apparent net uptake of cholesterol was considered to be due to exchange, since net loss of cholesterol from the growth medium was not detected. Although bile and bile salt-stimulated parasite growth was associated with enhanced lecithin uptake, reduction in generation time was observed at low bile and bile salt concentrations when lecithin uptake was similar to bile free controls. Thus, bile salts may stimulate Giardia growth initially by a mechanism independent of enhanced membrane phospholipid uptake. However, since Giardia has no capacity to synthesize membrane lipid, biliary lecithin may be a major source of phospholipid for growth of this parasite.

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M J Farthing, G T Keusch, M C Carey

Profiles of steady state levels of messenger RNAs coding for type I procollagen, elastin, and fibronectin in hamster lungs undergoing bleomycin-induced interstitial pulmonary fibrosis.

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We have characterized the messenger RNAs (mRNAs) coding for procollagen alpha 1(I), elastin, fibronectin, and actin in the lungs of Syrian golden hamsters by Northern blot analyses. While elastin, fibronectin, and beta-actin were each coded for by a single mRNA species of 4.1 kilobases (kb), 9.1 kb, and 2.1 kb in size, respectively, we identified a major (5.4 kb) and a minor (6.5 kb) procollagen alpha 1(I) mRNA species in the hamster lungs. The mRNAs for the three extracellular matrix proteins showed increased accumulation followed by steady decline in the bleomycin-treated lungs. There were significant differences among the three mRNAs in the relative increase and the time of maximum accumulation. After reaching the peak levels between 2-3 wk posttreatment, the levels of procollagen alpha 1(I) and elastin mRNAs declined to near normal values around the fourth week. In contrast, the accumulation of fibronectin mRNA was maximum in the first week after bleomycin treatment. The procollagen alpha 1(I) mRNA accumulated most dramatically (sevenfold above the levels in the untreated animals) compared with a five-fold increase in mRNA coding for fibronectin. Elastin mRNA increased approximately twofold above the control values. Nuclear runoff transcription experiments demonstrated a selective increase in the rates of transcription of genes coding for procollagen alpha 1(I), fibronectin, and elastin; the extent of transcriptional stimulation of procollagen alpha 1(I) and fibronectin genes was significantly greater than that of elastin. Since the amount of actin mRNA, as well as the rate of transcription of actin gene(s), varied only slightly after bleomycin treatment, we conclude that the metabolism of mRNAs coding for extracellular matrix proteins may be preferentially perturbed during pulmonary fibrosis.

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R Raghow, S Lurie, J M Seyer, A H Kang

Tracer norepinephrine kinetics in coronary circulation of patients with heart failure secondary to chronic pressure and volume overload.

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Controversy exists over the nature of the abnormality in cardiac sympathetic nerves in heart failure. In the cardiomyopathy of the Syrian hamster, reduction in tissue stores and increased turnover of norepinephrine is clearly associated with excessive sympathetic stimulation but in animal models and humans with heart failure secondary to mechanical overload there is evidence for depression of neuronal uptake. Because norepinephrine is both released and taken up by sympathetic fibers it is impossible to assess norepinephrine kinetics in an intact heart without separating these two functions. A technique for doing so has recently been developed in normal dogs and we therefore acquired similar data in humans with heart failure secondary to chronic pressure and volume overload. The technique involves the combination of transient norepinephrine tracer coronary sinus outflow in relation to intravascular and interstitial references after simultaneous injection into the left coronary artery and the measurement of endogenous norepinephrine concentrations in artery and coronary sinus. We found a marked reduction in cardiac norepinephrine release and uptake in a group of patients with clinical left ventricular failure secondary to mechanical overload, relative to a group of patients with no failure. Norepinephrine balance and overflow across the heart were not significantly different. We conclude that there is hypofunction of the cardiac sympathetic nerves in heart failure secondary to mechanical overload and that traditional methods are inadequate in assessing cardiac norepinephrine kinetics when there are simultaneous changes in neuronal uptake and release.

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C P Rose, J H Burgess, D Cousineau

Suppression of murine neuroblastoma growth in vivo by mevinolin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase.

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3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase catalyzes the formation of mevalonate, an essential precursor for isoprenoid compounds in mammalian cells. Recent studies have shown that mevinolin, a competitive inhibitor of the reductase, inhibits cell proliferation and induces differentiation in cultured C1300 (Neuro-2A) murine neuroblastoma cells. We now report that mevinolin can inhibit neuroblastoma growth in vivo. The specific activity of HMG-CoA reductase in subcutaneous neuroblastomas increased more than 20-fold between the fifth and eighth days after tumor inoculation, and remained elevated for the remainder of the tumor lifetime in mice. The increase in reductase activity was correlated with a marked increase in tumor DNA content and exponential increase in tumor weight. Using an in vitro assay to monitor the ability of mouse serum to suppress sterol synthesis, we determined that mevinolin was inactivated or cleared from the circulation within 3-6 h after a single subcutaneous injection. However, by using subcutaneous osmotic pumps to deliver a constant infusion of mevinolin, we were able to maintain adequate blood levels of the drug for 7 d. Mevinolin (5 mg/kg per h) suppressed tumor growth (wet weight) significantly when treatment was carried out between day 1 and day 8 or between day 5 and day 12 after tumor inoculation. Histopathological examination of tumors from mevinolin-treated mice revealed few or no mitotic figures and marked cellular degeneration. Measurements of incorporation of (3H)acetate into neuroblastoma sterols and ubiquinones 24 h after implantation of osmotic pumps showed that mevinolin produced a marked inhibition of isoprenoid synthesis in the tumors in vivo. The data suggest that, in addition to their demonstrated utility as cholesterol-lowering drugs, competitive inhibitors of HMG-CoA reductase may have considerable potential as novel antineoplastic agents.

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W A Maltese, R Defendini, R A Green, K M Sheridan, D K Donley

Therapeutic concentrations of glucocorticoids suppress the antimicrobial activity of human macrophages without impairing their responsiveness to gamma interferon.

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By exposing human blood-derived macrophages and alveolar macrophages in vitro to dexamethasone, we showed in these studies that glucocorticoids markedly suppress the antimicrobial activity of macrophages but not macrophage activation by lymphokines. As little as 2.5 X 10(-8) mol/liter of dexamethasone prevented macrophages from inhibiting germination of Aspergillus spores or from eliminating ingested bacteria such as Listeria, Nocardia, or Salmonella. Damage to macrophage function was inhibited by progesterone and appeared to be receptor-mediated. In accordance with in vivo observations, dexamethasone required 24-36 h to suppress antimicrobial activity. While glucocorticoids interfered with base-line activity of macrophages, dexamethasone concentrations comparable to drug levels in patients had no effect on macrophage activation. Proliferating lymphocytes and gamma-interferon thus increased the antimicrobial activity of phagocytes exposed to glucocorticoids over that of control cells. Macrophage activation and correction of the dexamethasone effect by gamma-interferon, however, was dependent on the pathogen. The lymphokine enhanced the antimicrobial activity of dexamethasone-treated macrophages against Listeria and Salmonella but not against Aspergillus or Nocardia. Dexamethasone-induced damage to the antimicrobial activity of human macrophages in vitro parallels observations that glucocorticoids render laboratory animals susceptible to listeriosis and aspergillosis by damaging resident macrophages. Suppression of macrophage antimicrobial activity should thus be considered when treating patients with glucocorticoids; its prevention by gamma-interferon might be beneficial for some but not all pathogens.

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A Schaffner

Mechanism of action of blocking immunoglobulin G for Neisseria gonorrhoeae.

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Blocking immunoglobulin G (IgG) inhibits complement-mediated killing of serum-resistant Neisseria gonorrhoeae (GC) in immune human serum. We examined the mechanism of action of blocking IgG. Presensitization of GC with increasing concentrations of blocking IgG or F(ab')2 before incubation with bactericidal antibody and absorbed pooled normal human serum increased consumption and deposition of the third component of human complement (C3) and the ninth component of human complement (C9) but inhibited killing in dose-related fashion. We next showed that blocking IgG or F(ab')2 partially inhibited binding of bactericidal IgG to GC. Also, binding of a monoclonal antibody recognizing GC outer membrane protein PIII was almost completely inhibited by blocking F(ab')2, confirming other work (Rice, P. A., M. R. Tam, and M. S. Blake, manuscript submitted for publication) showing that PIII is a target for blocking antibody. Studies of the C3 deposition site showed that one quarter of the C3 deposited on GC in the presence of blocking IgG bound covalently to the antibody molecule. Finally, 125I-GC constituents with covalently bound C3 were affinity purified on Sepharose bearing antibodies to C3 and identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis. C3 deposition on a 40,000-mol wt surface protein was enhanced six- to ninefold by blocking IgG, which indicates that the site of complement deposition was altered by blocking antibody. These studies show that blocking IgG competes with bactericidal antibody for binding to GC, but enhances rather than blocks complement activation, and leads to complement deposition at new sites that do not result in serum killing.

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K A Joiner, R Scales, K A Warren, M M Frank, P A Rice

Regulation of rat biliary cholesterol secretion by agents that alter intrahepatic cholesterol metabolism. Evidence for a distinct biliary precursor pool.

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Propensity for cholesterol gallstone formation is determined in part by biliary cholesterol content relative to bile salts and phospholipid. We examined the hypothesis that the rate of biliary cholesterol secretion can be controlled by availability of an hepatic metabolically active free cholesterol pool whose size is determined in part by rates of sterol synthesis, as reflected by activity of the primary rate-limiting enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase and of sterol esterification, as reflected by the activity of the enzyme acyl coenzyme A/cholesterol acyltransferase (ACAT). Rats were prepared with biliary, venous, and duodenal catheters. The enterohepatic circulation of biliary lipids was maintained constant by infusion of a bile salt, lecithin, cholesterol replacement solution. Administration of 25-hydroxycholesterol decreased HMG CoA reductase activity, increased ACAT activity, and decreased biliary cholesterol output 26% by 1 h. By 2 h, ACAT activity and biliary cholesterol secretion were at control levels. Administration of mevinolin, a competitive inhibitor of HMG CoA reductase, had no effect on ACAT activity and decreased biliary cholesterol secretion 16%. Administration of progesterone, an inhibitor of ACAT, had no effect on HMG CoA reductase and increased biliary cholesterol output 32% at 1 h. By 2 h, all parameters were near control levels. None of these agents had any significant effect on biliary bile salt or phospholipid secretion. Thus, acutely altering rates of esterification and/or synthesis can have profound effects on biliary cholesterol secretion independent of the other biliary lipids. These experiments suggest the existence of a metabolically active pool of free cholesterol that serves as a precursor pool for biliary cholesterol secretion. Furthermore, the size of this precursor pool is determined in part both by rates of cholesterol synthesis and esterification and is a key determinant of biliary cholesterol secretion.

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B G Stone, S K Erickson, W Y Craig, A D Cooper

Rates of noninsulin-mediated glucose uptake are elevated in type II diabetic subjects.

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Although insulin is extremely potent in regulating glucose transport in insulin-sensitive tissues, all tissues are capable of taking up glucose by facilitated diffusion by means of a noninsulin-mediated glucose uptake (NIMGU) system. Several reports have estimated that in the postabsorptive state the majority of glucose disposal occurs via a NIMGU mechanism. However, these estimates have been either derived or extrapolated in normal humans. In the present study we have directly measured NIMGU rates in 11 normal (C) and 7 Type II noninsulin-dependent diabetic subjects (NIDDM; mean +/- SE fasting serum glucose, 249 +/- 24 mg/dl). To accomplish this, the serum glucose was clamped at a desired level during a period of insulin deficiency induced by a somatostatin infusion (SRIF, 550 micrograms/h). With a concomitant [3-3H]glucose infusion, we could isotopically quantitate glucose disposal rates (Rd) during basal (basal insulin present) and insulin-deficient (SRIF) conditions. With this approach we found that (a) basal Rd was greater in NIDDM than in C, 274 +/- 31 vs. 150 +/- 7 mg/min, due to elevated hepatic glucose output, (b) NIMGU composes 75 +/- 5% of basal Rd in C and 71 +/- 4% in NIDDM, (c) NIDDMS have absolute basal NIMGU rates that are twice that of C (195 +/- 23 vs. 113 +/- 8 mg/min, P less than 0.05), (d) when C were studied under conditions of insulin deficiency (SRIF infusion) and at a serum glucose level comparable to that of the NIDDM group (250 mg/dl), their rates of NIMGU were the same as that of the NIDDM group (186 +/- 19 vs. 195 +/- 23 mg/min; NS). We conclude that (a) in the postabsorptive state, NIMGU is the major pathway for glucose disposal for both C and NIDDM; (b) for a given glucose level the efficiency of NIMGU (NIMGU divided by serum glucose level) is equal in C and NIDDM, but since basal Rd is elevated in NIDDMs their absolute basal rates of NIMGU are higher; and (c) elevated basal rates of NIMGU in NIDDM may play a role in the pathogenesis of the late complications of diabetes.

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A D Baron, O G Kolterman, J Bell, L J Mandarino, J M Olefsky

Calcium transport abnormality in uremic rat brain synaptosomes.

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Brain calcium is elevated in patients and laboratory animals with uremia. The significance of this finding is unclear. We evaluated calcium transport in brain of both normal and acutely uremic rats (blood urea nitrogen = 250 mg/dl) by performing studies in synaptosomes from rat brain cerebral cortex. Synaptosomes are vesicular presynaptic nerve endings from brain that contain mitochondria and are metabolically active. Two mechanisms of calcium transport were evaluated using radioactive 45Ca++ as a tracer. Both mechanisms were evaluated in the absence of exogenously administered parathyroid hormone (PTH). We first evaluated Na+-Ca++ exchange in vesicles that were loaded with NaCl in an external media containing 10 microM CaCl2. Both initial rates of calcium transport and equilibrium levels of calcium accumulation in synaptosomes prepared from uremic rats were significantly greater (P less than 0.005) than in normal. To assess calcium efflux, ATP-dependent calcium uptake (1 mM ATP) was studied in inverted plasma membrane vesicles loaded with KCl. In the uremic synaptosomes, a significant increase (P less than 0.005) in ATP-dependent calcium uptake was observed as compared with the normal. These studies show that (a) Calcium accumulation via the Na+-Ca++ exchanger is increased in synaptosomes prepared from uremic rat brain. (b) Calcium influx into inverted plasma membrane vesicles from uremic rats via the ATP-dependent calcium transport mechanism is increased when compared with normal. (c) The increased calcium accumulation in uremia by both Na+-Ca++ exchange and ATP-dependent calcium transport mechanism appears to be a result of increased synaptosomal membrane permeability to calcium. Both these abnormalities of calcium transport in uremia would tend to increase brain extracellular calcium in vivo. The defects observed in uremia do not appear to be readily reversible, and the relationship to PTH is presently unclear. These abnormalities may affect neurotransmission in the uremic state.

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C L Fraser, P Sarnacki, A I Arieff

Disparate mechanisms for hypoxic cell injury in different nephron segments. Studies in the isolated perfused rat kidney.

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Hypoxic injury was evaluated morphologically in the proximal tubule and in the medullary thick ascending limb of isolated rat kidneys perfused for 90 min without O2 or with various metabolic inhibitors. Inhibition of mitochondrial respiration (with rotenone, antimycin, oligomycin) or of intermediary metabolism (with monofluoroacetate, malonate, 2-deoxyglucose) caused reduction in renal oxygen consumption, renal function, and ATP content comparable with those elicited by oxygen deprivation. Metabolic inhibition produced hypoxiclike injury in the first portions of the proximal tubule, S1 and S2 ("clubbing" of microvilli, mitochondrial swelling), and the extent of damage was correlated with the degree of ATP depletion. In the third portion of the proximal tubule, S3, hypoxiclike damage (cytoplasmic edema or fragmentation) occurred most consistently when both aerobic and anaerobic metabolism were inhibited simultaneously. In the medullary thick ascending limb, none of the metabolic or mitochondrial inhibitors used could reproduce the injury of oxygen deprivation. Thus, the proximal tubule and the thick ascending limb have markedly different responses to cellular energy depletion, suggesting disparate mechanisms for hypoxic injury along the nephron.

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M Brezis, P Shanley, P Silva, K Spokes, S Lear, F H Epstein, S Rosen

Effect of atrial peptides on aldosterone production.

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This study examines the effects of the synthetic atrial peptides (atriopeptin I, II, and III) on aldosterone and corticosterone production by rat adrenal cell suspensions. Furthermore, we studied the effect of atriopeptin II infusion on the plasma aldosterone response to angiotensin II in the rat in vivo. Atriopeptin I, II, and III decreased aldosterone release from zona glomerulosa cells in a dose-dependent fashion. 10 pM atriopeptin II inhibited basal aldosterone release significantly (P less than 0.01), and 10 nM atriopeptin II or III lowered it by 79%. Atriopeptin II decreased the sensitivity of the glomerulosa cells to adrenocorticotropic hormone (ACTH) and angiotensin II. Atriopeptin II had no effect on basal or ACTH-stimulated corticosterone release by fasciculata-medullary cells. In vivo infusions of angiotensin II with or without simultaneous infusions of atriopeptin II showed that atriopeptin II significantly inhibited the aldosterone response to angiotensin II. This inhibition by atriopeptin II was independent of any effect on plasma renin activity, serum potassium, or ACTH. These data raise the possibility that the atrial natriuretic peptides may affect sodium excretion by the kidney, not only directly, but also indirectly through the inhibition of aldosterone production.

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K Atarashi, P J Mulrow, R Franco-Saenz

Bradykinin stimulation of oxidative metabolism in renal cortical tubules from rabbit. Possible role of arachidonic acid.

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Vasoactive peptides may have direct effects on both renal vasculature and renal tubules. In this study, we examined the direct and immediate effects of bradykinin on oxygen consumption by suspensions of cortical tubules from rabbit kidney. Bradykinin (10(-11) to 10(-7) M) stimulated oxygen consumption rates (QO2) in a dose-dependent manner with a maximal increase of +0.80 +/- 0.13 nmol X mg protein-1 X min-1. This stimulation was prevented by calcium-free media or by the addition of inhibitors of calcium transport, calcium-calmodulin complex formation, Na,K-ATPase activity, mitochondrial respiration, and phospholipase activity. Addition of bradykinin increased the ADP and AMP contents of cortical tubules without changing the ATP content. These data indicate that bradykinin stimulates ATP use and Na,K-ATPase activity. We also examined the effects of exogenous arachidonic acid on QO2 in cortical tubules. Acute additions of arachidonic acid stimulated QO2 at low concentrations (10(-8) to 10(-6) M) and uncoupled mitochondrial respiration at high concentrations (10(-5) M). The effect of arachidonic acid on adenosine nucleotide content was dose-dependent and indicated increased use of ATP. Bradykinin increased QO2 in the presence of low concentrations of arachidonic acid (10(-11) to 10(-9) M), but had no further effect on QO2 in the presence of higher concentrations of arachidonic acid (10(-8) to 10(-6) M). Bradykinin stimulation of QO2 was not prevented by inhibition of cyclooxygenase activity with indomethacin but was prevented by inhibition of lipoxygenase-like activity with nordihydroguariaretic acid. These results suggest that the bradykinin effect on QO2 may be mediated by arachidonic acid release and subsequent metabolism.

Authors

P C Brazy, D R Trellis, P E Klotman

Metabolic fate of extracted glucose in normal human myocardium.

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Glucose is an important substrate for myocardial metabolism. This study was designed to determine the effect of circulating metabolic substrates on myocardial glucose extraction and to determine the metabolic fate of glucose in normal human myocardium. Coronary sinus and arterial catheters were placed in 23 healthy male volunteers. [6-14C]Glucose was infused as a tracer in 10 subjects. [6-14C]Glucose and [U-13C]lactate were simultaneously infused in the other 13 subjects. Simultaneous blood samples were obtained for chemical analyses of glucose, lactate, and free fatty acids and for the the isotopic analyses of glucose and lactate. Glucose oxidation was assessed by measuring myocardial 14CO2 production. The amount of glucose extracted and oxidized by the myocardium was inversely correlated with the arterial level of free fatty acids (r = -0.71; P less than 0.0001). 20% (range, 0-63%) of the glucose extraction underwent immediate oxidation. Chemical lactate analysis showed a net extraction of 26.0 +/- 16.4%. However, isotopic analysis demonstrated that lactate was being released by the myocardium. In the 13 subjects receiving the dual-carbon-labeled isotopes, the lactate released was 0.09 +/- 0.04 mumol/ml and 49.5 +/- 29.5% of this lactate was from exogenous glucose. This study demonstrates that the circulating level of free fatty acids plays a major role in determining the amount of glucose extracted and oxidized by the normal human myocardium. Only 20.1 +/- 19.4% of the glucose extracted underwent oxidation, and 13.0 +/- 9.0% of the glucose extracted was metabolized to lactate and released by the myocardium. Thus, 60-70% of the glucose extracted by the normal myocardium is probably stored as glycogen in the fasting, resting state.

Authors

J A Wisneski, E W Gertz, R A Neese, L D Gruenke, D L Morris, J C Craig

Chloride secretory mechanism induced by prostaglandin E1 in a colonic epithelial cell line.

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Confluent T84 monolayers grown on permeable supports and mounted in a modified Ussing chamber secrete chloride (Cl-) in response to prostaglandin E1. The threshold stimulation was observed at 10(-9) M and a maximal effect at 10(-6) M. Unidirectional flux studies showed an increase in both serosal to mucosal and mucosal to serosal Cl- fluxes with 10(-6) M prostaglandin E1; the increase in serosal to mucosal Cl- flux exceeded the increase in mucosal to serosal flux, resulting in net Cl- secretion. Na+ transport was not affected in either direction and the changes in net Cl- flux correlated well with the changes in short circuit current. To identify the electrolyte transport pathways involved in the Cl- secretory process, the effect of prostaglandin E1 on ion fluxes was tested in the presence of putative inhibitors. Bumetanide was used as an inhibitor for the basolaterally localized Na+,K+,Cl- cotransport system whose existence and bumetanide sensitivity have been verified in earlier studies (Dharmsathaphorn et al. 1984. J. Clin. Invest. 75:462-471). Barium was used as an inhibitor for the K+ efflux pathway on the basolateral membrane whose existence and barium sensitivity were demonstrated in this study by preloading the monolayers with 86Rb+ (as a tracer for K+) and simultaneously measuring 86Rb+ efflux into both serosal and mucosal reservoirs. Both bumetanide and barium inhibited the net chloride secretion induced by prostaglandin E1 suggesting the involvement of the Na+,K+,Cl- cotransport and a K+ efflux pathways on the basolateral membrane in the Cl- secretory process. The activation of another Cl- transport pathway on the apical membrane by prostaglandin E1 was suggested by Cl- uptake studies. Our findings indicate that the prostaglandin E1-stimulated Cl- secretion, which is associated with an increase in cyclic AMP level, intimately involves (a) a bumetanide-sensitive Na+,K+,Cl- cotransport pathway that serves as a Cl- uptake step across the basolateral membrane, (b) the stimulation of a barium-sensitive K+ efflux mechanism on the basolateral membrane that most likely acts to recycle K+, and (c) the activation of a Cl- transport pathway on the apical membrane that serves as a Cl- exit pathway.

Authors

A Weymer, P Huott, W Liu, J A McRoberts, K Dharmsathaphorn

Synergistic action of cyclic adenosine monophosphate- and calcium-mediated chloride secretion in a colonic epithelial cell line.

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Vasoactive intestinal polypeptide (VIP) and the calcium ionophore A23187 caused dose-dependent changes in the potential difference and the short circuit current (Isc) across confluent T84 cell monolayers mounted in modified Ussing chambers. Both VIP and A23187 stimulated net chloride secretion without altering sodium transport. Net chloride secretion accounted for the increase in Isc. When A23187 was tested in combination with VIP, net chloride secretion was significantly greater than predicted from the calculated sum of their individual responses indicating a synergistic effect. VIP increased cellular cyclic AMP (cAMP) production in a dose-dependent manner, whereas A23187 had no effect on cellular cAMP. We then determined whether VIP and A23187 activated different transport pathways. Earlier studies suggest that VIP activates a basolaterally localized, barium-sensitive potassium channel as well as an apically localized chloride conductance pathway. In this study, stimulation of basolateral membrane potassium efflux by A23187 was documented by preloading the monolayers with 86Rb+. Stimulation of potassium efflux by A23187 was additive to the VIP-stimulated potassium efflux. By itself, 0.3 microM A23187 did not alter transepithelial chloride permeability, and its stimulation of basolateral membrane potassium efflux caused only a relatively small amount of chloride secretion. However, in the presence of an increased transepithelial chloride permeability induced by VIP, the effectiveness of A23187 on chloride secretion was greatly augmented. Our studies suggest that cAMP and calcium each activate basolateral potassium channels, but cAMP also activates an apically localized chloride channel. Synergism results from cooperative interaction of potassium channels and the chloride channel.

Authors

C A Cartwright, J A McRoberts, K G Mandel, K Dharmsathaphorn

Mechanoelectrical feedback: independent role of preload and contractility in modulation of canine ventricular excitability.

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Mechanoelectrical feedback, defined as changes in mechanical state that precede and alter transmembrane potential, may have potential importance in understanding the role of altered load and contractility in the initiation and modulation of ventricular arrhythmias. To assess the independent effects of preload and contractility on myocardial excitability and action potential duration, we determined the stimulus strength-interval relationship and recorded monophasic action potentials in isolated canine left ventricles contracting isovolumically. The strength-interval relationship was characterized by three parameters: threshold excitability, relative refractory period, and absolute refractory period. The effects of a threefold increase in left ventricular volume or twofold increase in contractility on these parameters were independently assessed. An increase in preload did not change threshold excitability in 11 ventricles but significantly shortened the absolute refractory period from 205 +/- 15 to 191 +/- 14 ms (P less than 0.001) (mean +/- SD). Similarly, the relative refractory period decreased from 220 +/- 18 to 208 +/- 19 ms (P less than 0.002). Comparable results were observed when contractility was increased as a result of dobutamine infusion in 10 ventricles. That is, threshold excitability was unchanged but the absolute refractory period decreased from 206 +/- 14 to 181 +/- 9 ms (P less than 0.003), and the relative refractory period decreased from 225 +/- 17 to 205 +/- 18 ms (P less than 0.003). Similar results were obtained when contractility was increased with CaCl2, indicating that contractility associated changes were independent of beta-adrenergic receptor stimulation. An increase in preload or contractility was associated with shortening of the action potential. A threefold increase in preload and twofold increase in contractility were associated with a decrease in action potential duration of 22 and 24 ms, respectively. There was a significant linear correlation between action potential duration and excitability (absolute refractory period). The similar effects of increased preload and contractility on threshold excitability and refractoriness can be explained by the action these perturbations have on the time course of repolarization. Therefore, excitability of the ventricle is sensitive to and is modulated by alteration of load or inotropic state. The similar effects of either increased preload or contractility on excitability may be mediated by a common cellular mechanism which results in a rise in intracellular free Ca2+ and secondary abbreviation of the action potential.

Authors

B B Lerman, D Burkhoff, D T Yue, M R Franz, K Sagawa

Inhibition of parathyroid hormone secretion and parathyroid hormone-independent diminution of tubular calcium reabsorption by WR-2721, a unique hypocalcemic agent.

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Hypocalcemia has been observed in patients receiving WR-2721 [S-,2-(3-aminopropylamino)-, ethylphosphorothioic acid]. WR-2721 is a compound that, after being dephosphorylated, provides protection of normal tissues against radio- and chemotherapy. The hypocalcemic response was accompanied by a decrease in the plasma level of parathyroid hormone (PTH) and by hypomagnesemia. Our present studies in rats on the mechanism of the hypocalcemic effect of WR-2721 indicate that: (a) The phosphorylated and dephosphorylated form of WR-2721 induced an equal dose-dependent decrement in plasma calcium. (b) In intact rats a maximal hypocalcemic dose of WR-2721 reduced urinary cyclic AMP excretion from 70.5 +/- 6.3 to 38.2 +/- 3.1 pmol/ml glomerular filtration rate (GFR), a level comparable to that observed (35.9 +/- 5.2 pmol/ml GFR) in thyroparathyroidectomized (TPTX) rats. (c) WR-2721 given to TPTX rats did not significantly interfere with the calcemic effect of bovine PTH 1-34 infused at 2.5 IU/h. Likewise, the drug did not impair the PTH actions on the renal Ca and inorganic phosphate (Pi) handling, and on the urine cyclic AMP excretion. (d) In TPTX rats made normocalcemic by low Pi diet, the hypocalcemic effect of WR-2721 was only about 25% of that observed in intact animals. However, it was associated with increased urine Ca per milliliter GFR, indicating a PTH-independent inhibitory effect on tubular Ca reabsorption. (e) In WR-2721-treated intact rats, prevention of hypomagnesemia by infusing magnesium chloride did not reduce hypocalcemia. In conclusion, the hypocalcemic effect of WR-2721 is not dependent upon the presence of a phosphate group in the molecule and is not causally related to hypomagnesemia. WR-2721 appears to be a unique hypocalcemic pharmacologic agent with strong inhibitory activity on PTH secretion and additional PTH-independent action on renal Ca reabsorption.

Authors

S Hirschel-Scholz, J Caverzasio, J P Bonjour

Characterization of human platelet vasopressin receptors.

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Abstract

Using tritiated arginine-8-vasopressin [3H]AVP, vasopressin-specific binding sites were detected on human platelet membranes. One class of high-affinity binding sites was characterized with an equilibrium dissociation constant of 1.01 +/- 0.06 nM and a maximal binding capacity of 100 +/- 10 fmol/mg of protein (n = 12). Highly significant correlations were found between the relative agonistic (r = 0.87, P = 0.002) or antagonistic (r = 0.99, P = 0.007) vasopressor activities of a series of 13 AVP structural analogues and their relative abilities to inhibit [3H]AVP binding to platelet receptors whereas no such relationship existed when antidiuretic activities were considered (r = 0.28, P = 0.47). AVP did not stimulate cyclic AMP production of human platelets; on the contrary, high AVP concentrations (10(-6) M) inhibited cyclic AMP production measured in basal and prostaglandin E1-stimulated conditions. AVP caused intact platelet aggregation with a half-maximal aggregation (EC50) of 28 +/- 2 nM. This effect was more potently reversed by the specific vascular antagonist d(CH2)5Tyr(Me)AVP (pA2 = 8.10 +/- 0.23) than by the specific renal antagonist d(CH2)5IleuAlaAVP (pA2 = 6.67 +/- 0.12). The pA2 values of these two antagonists in platelets are in close agreement with the pKi values obtained in competition experiments (respectively 8.59 and 6.93) and with pA2 values reported in the literature for their in vivo antivasopressor activity (respectively 8.62 and 6.03). The observation that human platelets bear AVP receptors belonging to the vascular class suggests that platelet receptors can be used to further explore the role of vasopressin in cardiovascular homeostasis.

Authors

M Thibonnier, J M Roberts

Spontaneous immunoglobulin A secretion and lack of mitogen-responsive B cells in systemic lupus erythematosus.

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Abstract

In an analysis of lymphocyte functions of systemic lupus erythematosus (SLE) patients, B cell abnormalities such as a lack of mitogen-responsive B cells and a predominance of spontaneous IgA-secreting cells (SC) were found. Lymphocyte functions of 20 SLE patients were studied. Impaired proliferative response to B cell mitogen, Staphylococcus aureus strain Cowan I (Cowan I), was observed, whereas the response to T cell mitogen phytohemagglutinin was normal. High levels of spontaneous IgA-SC were observed in SLE patients (greater than 10(2) cells/10(4) peripheral blood mononuclear cells [PBMC]), whereas spontaneous IgM-, IgG-, or IgE-SC were not proportionately increased. The number of spontaneous IgA-SC decreased with time in culture and became undetectable by day 5 of culture. In contrast, spontaneous immunoglobulin- (IgM, IgG, and IgA) SC were not observed in healthy volunteers (less than 10 cells/10(4) PBMC). Moreover, in SLE patients failure of induction of immunoglobulin-secreting cells (ISC) was observed when B cells were stimulated by Cowan I and B cell differentiation factor at any day tested, whereas ISC were induced in healthy volunteers on day 6 of culture. Depletion of T cells or macrophages did not affect the results obtained. These results suggest that the abnormalities observed in SLE B cells are not due to the in vitro direct effects of suppressor macrophages or suppressor T cells, and that the condition of the predominance of spontaneous IgA-SC and the unresponsiveness to exogenous stimulation may be emblematic of hyperactive B cells in SLE.

Authors

O Saiki, Y Saeki, S Kishimoto

Calcium uptake by intestinal brush border membrane vesicles. Comparison with in vivo calcium transport.

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Abstract

In prior studies, we examined kinetics of steady state in vivo transepithelial calcium transport in rat and hamster. The present studies related calcium uptake by the brush border to in vivo transport. We measured calcium uptake by brush border membrane vesicles from the two species. In the rat, our prior in vivo studies had shown that (a) calcium transport was mediated, (b) no nonmediated component was detectable, and (c) Vmax was 2.5 times greater in proximal than distal small intestine. In brush border membrane vesicles from the rat, Vmax for the saturable component of calcium uptake was again 2.5 times greater in proximal than distal intestine. Contrasting with in vivo studies, a major nonsaturable component was present in vesicles from proximal and distal small intestine. In the hamster, our previous in vivo studies had shown (1) both mediated and nonmediated components of calcium transport, (2) greater nonmediated transport in proximal than distal small intestines, and (3) Vmax for calcium transport twice as great in distal as in proximal small intestine. In the present study with brush border membrane vesicles from hamster, Vmax for saturable calcium transport was again twice as great in distal as in proximal small intestine. However, nonsaturable calcium transport rates relative to saturable rates were much greater with vesicles than in in vivo studies, and were greater in vesicles from distal than proximal small intestine. Since rates of saturable calcium uptake by brush border membrane vesicles parallel corresponding in vivo mediated transport rates, we conclude that the segmental rates of calcium transport in rat and hamster could be determined by brush border function.

Authors

H P Schedl, H D Wilson

Vitamin K-dependent carboxylation and vitamin K metabolism in liver. Effects of warfarin.

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Abstract

The systems involved in vitamin K-dependent carboxylation and vitamin K metabolism have been extensively studied in rat liver. To determine how clinically applicable this information is, similar in vitro studies were completed using human liver. One major difference exists in the pathways that provide reduced vitamin K1 cofactor for the carboxylation reaction. The coumarin-sensitive DT-diaphorase (EC.1.6.99.2) in human liver appears to play a relatively minor role in the dehydrogenase pathway. However, similar to rat liver, the human liver contains a warfarin-insensitive enzyme in this dehydrogenase pathway. The data suggest that this enzyme is responsible for the antidotic effect of vitamin K1 in cases of coumarin intoxication. Human vitamin K epoxide reductase, which constitutes the other pathway for vitamin K1 reduction, has kinetic and enzymological characteristics that are very similar to the rat enzyme. This enzyme exhibited similar activity in rat and human microsomes. Initial velocities for vitamin K1 epoxide reduction in rat and human microsomes were 20 and 32 pmol/mg X min, respectively. The human enzyme is highly sensitive to warfarin inhibition. The mechanism for this inhibition appears to be similar to what has been proposed for the rat enzyme. Also, a vitamin K-dependent carboxylation system is described that allows both pathways to support the carboxylation reaction with reduced vitamin K1 cofactor. The effect of warfarin on this in vitro system is consistent with the current model for the mechanism of action of coumarin anticoagulant drugs in the rat.

Authors

R Wallin, L F Martin

Studies on multiple thyroid cell membrane-directed antibodies in Graves' disease.

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Abstract

Immunoglobulin G was obtained from the serum of a woman who had given birth to three children with a delayed onset of hyperthyroidism; the clinical events were due to the coexistence of thyroid-stimulating antibody (TSAb) and an inhibitor of TSAb in the maternal serum. The current studies explore the possible existence of additional thyroid membrane-directed antibodies. Human thyroid slices, cells in monolayer culture, and functioning rat thyroid cells (FRTL5), with measurement of cyclic AMP concentration, were used for TSAb assays. Assays of the inhibition of binding of 125I-thyrotropin (TSH) to its receptor used human thyroid and FRTL5 cells, and human thyroid and guinea pig fat cell membranes as receptors. All activities were associated with IgG kappa. Fractions of IgG kappa obtained by adsorption to and the desorption from human thyroid and guinea pig fat cell preparations and F(ab')2 and Fab fragments of the parent IgG were tested. Results indicated that there were three activities in the IgG, namely, TSAb; an inhibitor of TSH-binding that was active in all species and preparations tested, and was effective as Fab and F(ab')2 on both particulate and solubilized thyroid membranes; and an enhancer of TSH-binding (e.g., approximately equal to 220% increase in binding) that was relatively specific for human thyroid membranes only in particulate form, was not adsorbed by fat, and was active as F(ab')2, but minimally as Fab. The concept is developed that dilution of the total IgG, experimentally in vitro or by metabolic clearance in vivo in neonates, determines the effect on either thyroid stimulation or TSH-binding. The incidence of such multiple antibodies and their interaction remains to be determined.

Authors

M Zakarija, A Garcia, J M McKenzie

Altered proopiomelanocortin gene expression in adrenocorticotropin-producing nonpituitary tumors. Comparative studies with corticotropic adenomas and normal pituitaries.

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Abstract

In order to assess the mechanisms of proopiomelanocortin (POMC) gene expression in human ACTH-producing tumors, we performed the simultaneous evaluation of POMC products and messenger RNA (mRNA) in tissue fragments obtained from two corticotropic adenomas, five nonpituitary tumors, and two normal human pituitaries. The POMC products were examined using a combination of gel exclusion chromatography and four different radioimmunoassays directed against gamma 3 melanocyte stimulating hormone (gamma 3MSH), ACTH, gamma-lipotropin (gamma LPH), and beta-endorphin. The POMCmRNA was detected and analyzed by dot and northern blot hybridization using a single-stranded genomic DNA probe corresponding to the coding region of the human POMC gene. Tissue concentrations of POMC products and mRNA showed parallel distributions. Immunoreactive gamma 3MSH and gamma LPH patterns revealed only 16-kD fragment- and gamma LPH-like peptides in normal and tumoral pituitaries; additional gamma 3MSH- and/or beta MSH-like peptides were found in all five nonpituitary tumors. A single POMCmRNA of approximately 1,200 bases (b) was detected in normal and tumoral pituitaries; a single identical POMCmRNA was also found in four nonpituitary tumors. A thymic carcinoid tumor, in addition to the 1,200-b POMCmRNA, contained equal amounts of a second larger POMCmRNA of approximately 1,450 b. It is concluded that POMC gene expression appears qualitatively unaltered in corticotropic adenomas. In nonpituitary tumors, in contrast, abnormal POMC processing is frequent; in addition, an extra POMCmRNA was detected in a thymic tumor with a greater length than the normal mRNA; the mechanisms and pathophysiological implications of these modifications remain to be elucidated.

Authors

Y de Keyzer, X Bertagna, F Lenne, F Girard, J P Luton, A Kahn

A kallikrein-like serine protease in prostatic fluid cleaves the predominant seminal vesicle protein.

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Abstract

A 33-kD glycoprotein, known as the "prostate-specific antigen," was purified to homogeneity from human seminal plasma. The prostatic protein was identified as a serine protease, and its NH2-terminal sequence strongly suggests that it belongs to the family of glandular kallikreins. The structural protein of human seminal coagulum, the predominant protein in seminal vesicle secretion, was rapidly cleaved by the prostatic enzyme, which suggests that this seminal vesicle protein may serve as the physiological substrate for the protease. The prostatic enzyme hydrolyzed arginine- and lysine-containing substrates with a distinct preference for the former. All synthetic substrates tested were poor substrates for the enzyme. Synthetic Factor XIa substrate (pyro-glutamyl-prolyl-arginine-p-nitroanilide), and the synthetic kallikrein substrate (H-D-prolyl-phenylalanyl-arginine-p-nitroanilide) were hydrolyzed with maximum specific activities at 23 degrees C of 79 and 34 nmol/min per mg and Km values of 1.0 and 0.45 mM, respectively. Synthetic substrates for plasmin, chymotrypsin, and elastase were either not hydrolyzed by the enzyme at all, or only hydrolyzed very slowly.

Authors

H Lilja

Hepatic microcirculation in the perfused cirrhotic rat liver.

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Abstract

Liver microcirculation in the perfused rat liver was assessed by the multiple indicator dilution technique. Comparative studies were carried out in noncirrhotic rats and in rats with cirrhosis secondary to chronic exposure to phenobarbital and carbon tetrachloride. The alterations of the sinusoidal bed were characterized by changes in the displacement of hepatic venous outflow curves of various diffusible substances (labeled albumin, sucrose, and water) relative to that of labeled erythrocytes (vascular reference). Outflow recoveries of lidocaine (a substance that penetrates the liver cell membrane freely and completely) and of labeled microspheres (15 microns diam) were also appraised. In all cirrhotic rats, unimodal erythrocytes and albumin curves were obtained. The sinusoidal space was significantly decreased when compared with normal rats (P less than 0.001) and the total space accessible to albumin became progressively restricted. In seven cirrhotic rats, the profiles of labeled sucrose and water curves were compatible with a flow-limited diffusion and the total distribution volumes were not significantly different from values found in noncirrhotic rats (P = NS), which indicates that sucrose and water were still able to diffuse into an extravascular space not accessible to albumin. In the other cirrhotic rats, labeled sucrose and water curves showed progressive bimodal changes not compatible with a flow-limited diffusion. Such alterations were not due to large intrahepatic shunts, since only 0.25% of the 15-microns microspheres were recovered in the outflow of cirrhotic rats. However, an early lidocaine outflow peak related in time to the peak erythrocyte curve was observed in cirrhotic, but not in noncirrhotic, rats. Lidocaine recovery varied greatly in cirrhotic rats and appeared to increase as the liver disease progressed. These data can be explained by capillarization of sinusoids and/or by the development of channels with poor permeability. Electron microscopic observations of these rat livers favored the latter. Thus, in cirrhotic rat liver, two kinds of alteration are likely: (a) the vascular space is decreased with collagenization of the extravascular space, limiting the diffusion of large molecules such as albumin; and (b) small channels with poorly permeable walls develop, limiting the diffusion of small molecules such as lidocaine, sucrose, and water. Large intrahepatic shunts are not a common feature.

Authors

F Varin, P M Huet

Role of renal sympathetic nerves in mediating hypoperfusion of renal cortical microcirculation in experimental congestive heart failure and acute extracellular fluid volume depletion.

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Abstract

To evaluate the pathophysiologic importance of renal nerves in regulating the renal vasomotor tone, we measured several parameters of renal cortical microcirculation before and after acute renal denervation (DNx) in the following three groups of anesthetized Munich-Wistar rats: (group 1) congestive heart failure after surgically induced myocardial infarction (n = 10), (group 2) acute extracellular fluid volume depletion after deprivation of drinking water for 48 h (n = 8), and (group 3) sham or nontreated controls (n = 6). In the myocardial-infarcted rats, DNx led to a uniform increase in glomerular plasma flow rate of, on average, 36%. Single nephron glomerular filtration rate of myocardial-infarcted rats also increased despite a reduction in glomerular capillary hydraulic pressure. These changes were associated with a fall in arteriolar resistances, particularly in the efferent arteriole. The glomerular capillary ultrafiltration coefficient rose in all but one myocardial-infarcted animal. A similar hemodynamic pattern was seen after DNx in water-deprived animals. In every water-deprived animal, glomerular plasma flow rate and single nephron GFR increased on average by 28 and 14%, respectively. Again, afferent and efferent arteriolar resistances decreased significantly. Furthermore, the ultrafiltration coefficient increased uniformly and substantially with DNx. To ascertain the potential importance of the interaction between the renal nerves and angiotensin II in these circumstances, we compared the renal cortical hemodynamics in additional groups of water-deprived rats (group 4) after DNx (n = 15), (group 5) during inhibition of angiotensin II with saralasin (n = 15), and (group 6) during treatment with both saralasin and DNx (n = 15). No appreciable difference was detected between group 4 vs. 6. In contrast, substantial differences were noted between group 5 vs. 6: on average, the glomerular plasma flow rate was 26% higher and the afferent and efferent arteriolar resistances 25% and 27% lower, respectively, in group 6. These observations provide direct evidence to indicate pathophysiologic importance of renal nerves in the profound intrarenal circulatory adjustments in prerenal circulatory impairment. The vasoconstrictive effects of renal nerves appear to be mediated in part by their stimulatory influence on angiotensin II release and their direct constrictor actions on pre- and post-glomerular vessels as well.

Authors

V Kon, A Yared, I Ichikawa

Inner-ring deiodination of 3,5,3'-triiodothyronine in the in situ perfused guinea pig placenta.

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Abstract

Broken cell preparations of rat and human placentas contain an inner (tyrosyl)-ring iodothyronine deiodinase enzyme with greatest activity when the substrate is 3,5,3'-triiodothyronine (T3). This report describes the deiodination of T3 in the intact placenta and the effect of sodium iopanoate (IA) and propylthiouracil (PTU) on T3 deiodination. Under nembutal anesthesia, the placenta of 60-65-d-old pregnant guinea pigs was surgically exposed, a single umbilical artery and the umbilical vein were cannulated, and the fetus was removed. In a temperature-controlled chamber (37 degrees C), the fetal side of the placenta was perfused through the umbilical artery at a rate of 1 ml/min with 3% bovine serum albumin Krebs-Henseleit buffer containing 0.14 nM outer ring labeled [125I]T3. Placenta effluent fractions were collected at timed intervals from the umbilical vein cannula throughout a 120-min perfusion period. The contents of the perfusion buffer and the various effluent fractions were analyzed for their iodothyronine content by high pressure liquid chromatography. In five experiments, the percent composition of 125I-labeled iodothyronines in the perfusion buffer and placenta effluent was 95.3 +/- 1.0 (mean +/- SE) and 70.2 +/- 2.1 for T3 (P less than 0.01), 2.5 +/- 0.7 and 20.1 +/- 1.8 for 3,3'-T2 (P less than 0.01), and 0 and 8.2 +/- 0.9 for 3'-T1. There was no difference between the percent [125I]iodide in the perfusion buffer and in the placenta effluents. When placentas were perfused with IA and [125I]T3, after perfusion with [125I]T3 alone, there was a significant increase (P less than 0.01) in the percent [125I]T3 in the placenta effluents, and a significant decrease in [125I]3,3'-T2 (P less than 0.01) and [125I]3'-T1 (P less than 0.01). In contrast, PTU did not affect the composition of labeled iodothyronines in the placenta effluents, despite the fact that the addition of PTU significantly (P less than 0.001) inhibits the inner-ring deiodination of [125I]T3 in human or guinea pig placenta microsomes in the presence of low (0.25 mM) concentrations of dithiothreitol. The present studies demonstrate that T3 is actively deiodinated in the inner ring to 3,3'-T2 by the intact guinea pig placenta. A portion of 3,3'-T2 is further deiodinated in the inner ring to generate 3'-T1. No outer ring deiodination of T3 was seen under the conditions employed. IA, but not PTU, inhibits T3 deiodination in the placenta perfused in situ. We conclude that the placenta is probably a site for fetal T3 metabolism.

Authors

M I Castro, L E Braverman, S Alex, C F Wu, C H Emerson

Membrane markers, target cell specificity, and sensitivity to biological response modifiers distinguish human natural cytotoxic from human natural killer cells.

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Abstract

In the present report, we provide evidence for the distinct existence of a human natural cytotoxic (HNC) cell. This HNC cell can be identified by the monoclonal antibody HNC-1A3 and by the absence of the T10 antigen, other antigenic markers being shared, at least in part, with natural killer (NK) cells, T cells, or monocytes. In addition, the HNC cell preferentially kills the MA-160 target, the herpes simplex virus-1-infected MA-160 cell line, and the two human tumor cell lines HEp-2 and HF-2. It has weak lytic activity against the NK-sensitive K562 cell line or its relatively NK-resistant clone I subline. The cytotoxic activity of the HNC cell is not augmented by interferon but is markedly enhanced by interleukin 2 and by a measles-virus-induced factor (MVF). Furthermore, it is not inhibited by cyclosporin A (CsA), in contrast to NK cell cytotoxicity against the K562 target cell line which is augmented by interferon, inhibited by CsA, and not affected by MVF. These data suggest that spontaneously cytotoxic cells may belong to more than one subset of human lymphocytes, and that HNC cells may be defined in man using membrane markers, target cell specificity, and sensitivity to biological response modifiers.

Authors

M Rola-Pleszczynski, H Lieu, A K Sullivan, M Girard

Activation of the human neutrophil nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase by protein kinase C.

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Abstract

A variety of phagocytosable and soluble agonists stimulate the human neutrophil respiratory burst enzyme, NADPH-oxidase, an activity required for normal microbicidal function. Of these agonists, the phorbol esters, which stimulate diverse systems by their ability to substitute for diacylglycerol to activate protein kinase C (the major phorbol ester receptor), have now been shown to directly stimulate NADPH-oxidase through this same receptor. Almost 90% of the specific receptors for phorbol 12,13-dibutyrate (PDBu) were found in the cytosol upon subcellular fractionation. The dissociation constant for [3H]PDBu was 1.2 nM. No significant difference was found in the distribution of the receptor between subcellular fractions from resting as compared with phorbol 12-myristate 13-acetate (PMA)-stimulated neutrophils. On the basis of these binding studies, we were able to establish a reconstituted system in which PMA activated dormant NADPH-oxidase in a light membrane fraction when cytosol, NADPH, phosphatidylserine, or phosphatidylinositol and ATP were added. The calcium chelator, EGTA, inhibited the activation, which suggested a requirement for calcium at low concentrations. The half-maximally effective PMA dose was 1.1 nM, as predicted from the receptor content in these preparations. Reconstitution of oxidase activity was rapid, peaking within 1 min of incubation. Purified protein kinase C was able to substitute for the cytosol fraction, and accounted for 80% of the cytosol activity. These studies demonstrate that phorbol esters stimulate the neutrophil respiratory burst through activation of cytosolic protein kinase C, which in turn activates either a regulatory constituent or the NADPH-oxidase directly in the plasma membrane to generate an active O-2-generating system.

Authors

J A Cox, A Y Jeng, N A Sharkey, P M Blumberg, A I Tauber

Distribution of renin activity and angiotensinogen in rat brain. Effects of dietary sodium chloride intake on brain renin.

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Abstract

The purpose of this study was to investigate the biochemistry and the regulation of the brain renin-angiotensin system in the Sprague-Dawley rat. Renin activity and angiotensinogen concentrations (direct and indirect radioimmunoassays) were measured in several brain areas and in neuroendocrine glands. Regional renin activities were measured in separate groups of rats on high and low NaCl diets. Mean tissue renin activities ranged from 2.2 +/- 0.6 to 54.4 +/- 19.7 fmol/mg protein per h (mean of 7 +/- SD), with the highest amounts in pineal, pituitary, and pons-medulla. NaCl depletion increased renin activity in selected regions; based on estimates of residual plasma contamination (despite perfusion of brains with saline), increased renin activity of pineal gland and posterior pituitary was attributed to higher plasma renin. To eliminate contamination by plasma renin, 16-h-nephrectomized rats were also studied. In anephric rats, NaCl depletion increased renin activity by 92% in olfactory bulbs and by 97% in anterior pituitary compared with NaCl-replete state. These elevations could not be accounted for by hyperreninemia. Brain renin activity was low and was unaffected by dietary NaCl in amygdala, hypothalamus, striatum, frontal cortex, and cerebellum. In contrast to renin, highest angiotensinogen concentrations were measured in hypothalamus and cerebellum. Overall, angiotensinogen measurements with the direct and the indirect assays were highly correlated (n = 56, r = 0.96, P less than 0.001). We conclude that (a) NaCl deprivation increases renin in olfactory bulbs and anterior pituitary of the rat, unrelated to contamination by plasma renin; and (b) the existence of angiotensinogen, the precursor of angiotensins, is demonstrated by direct radioimmunoassay throughout the brain and in neuroendocrine glands.

Authors

C P Genain, G R Van Loon, T A Kotchen

3-Hydroxy-3-methylglutaryl coenzyme A reductase in anencephalic and normal human fetal liver.

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Abstract

In previous investigations, we have found that the liver appears to be the major source of cholesterol in the human fetus, and, in particular, a principal source of circulating low density lipo-protein-cholesterol (LDL-C). LDL-C plasma levels are low in the normal fetus, most likely due to the rapid uptake and metabolism by the fetal adrenal as precursor for steroid hormone biosynthesis. In contrast, in the anencephalic fetus the adrenals are atrophic, the rate of estrogen and glucocorticoid production is low, and the levels of LDL-C in fetal plasma are high. The purpose of the present investigation was to determine the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the primary rate-limiting enzyme of cholesterol biosynthesis, in anencephalic liver and normal fetal liver. We found that the specific activity of HMG-CoA reductase in normal fetal liver microsomes was 0.428 +/- 0.054 nmol mevalonate formed times mg-1 protein X min-1 (mean +/- SE, n = 9). The rate of HMG-CoA reductase in anencephalic liver microsome preparations was 10-fold less (0.040 +/- 0.003) (mean +/- SE, n = 7) P less than 0.001. Furthermore, we detected HMG-CoA reductase (97,000-mol wt protein) in normal human fetal liver after SDS PAGE and immunoblotting by using a monoclonal antibody directed against HMG-CoA reductase. We were unable to detect any significant quantity of HMG-CoA reductase protein in anencephalic fetal liver, which indicates that low reductase activity was due to low amounts of enzyme protein rather than inactive enzyme. In summary, we conclude that the low levels of cholesterol synthesis observed in anencephalic fetal liver are probably due to both the high levels of LDL-C in fetal plasma as well as the presence of low circulating levels of estrogens and glucocorticoids and that these factors regulate cholesterol synthesis both in vivo and in vitro in fetal liver. This occurs most probably by the modulation of the amount of HMG-CoA reductase, a primary rate-limiting and regulatory enzyme of the cholesterol biosynthetic sequence.

Authors

B R Carr, W E Rainey, J I Mason

Independent modulation of von Willebrand factor and fibrinogen binding to the platelet membrane glycoprotein IIb/IIIa complex as demonstrated by monoclonal antibody.

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Abstract

In this study we have used two new monoclonal antibodies, designated LJP5 and LJP9, as well as a previously described one, AP2, all specific for the platelet membrane glycoprotein (GP)IIb/IIIa complex. None of them reacted with dissociated GPIIb or GPIIIa. The monovalent Fab fragment of both LJP5 and LJP9 bound to unstimulated platelets in a saturable manner, but binding was markedly decreased after platelets had been incubated at 37 degrees C in the absence of added extracellular calcium. The binding of LJP9 was not affected by AP2, but was blocked by excess LJP5. On the contrary, the binding of LJP5 was blocked in the presence of both AP2 and LJP9. Thus, these antibodies bound to distinct epitopes of GPIIb/IIIa. At saturation, the binding to unstimulated platelets was between 2.41 and 10.9 X 10(4) molecules/platelet for LJP5 and between 3.47 and 9.1 X 10(4) molecules/platelet for LJP9 (range of 11 and 10 experiments, respectively). Binding increased up to 50% after thrombin stimulation. The estimated association constant, Ka, was 2.7 X 10(7) M-1 for LJP5 and 3.85 X 10(7) M-1 for LJP9. Both LJP5 and LJP9 partially inhibited the association of 45Ca2+ with the surface of unstimulated platelets. Moreover, both antibodies blocked the binding of von Willebrand factor (vWF) to stimulated platelets, whereas only LJP9, but not LJP5, blocked fibrinogen binding. LJP9 was also a potent inhibitor of platelet aggregation, whereas LJP5 was without effect in this regard. The results of the present study demonstrate that independent modulation of vWF and fibrinogen binding to stimulated platelets can be attained with monoclonal antibodies directed against distinct epitopes of GPIIb/IIIa.

Authors

V T Lombardo, E Hodson, J R Roberts, T J Kunicki, T S Zimmerman, Z M Ruggeri

Production of and in vitro response to interleukin 2 in the acquired immunodeficiency syndrome.

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Abstract

To test the hypothesis that deficient interleukin 2 (IL-2) secretion may underlie the impaired capacity of T cells from patients with Acquired Immunodeficiency Syndrome (AIDS) and the AIDS-related complex (ARC) to generate the macrophage-activating lymphokine, gamma interferon (IFN-gamma), we used five specific microbial antigens to examine IL-2 production. Mononuclear cells from only one of 32 (3%) AIDS patients secreted normal levels of IL-2, and 21 (66%) failed to produce any detectable IL-2. For 36 ARC patients, IL-2 generation was normal in nine (25%) and absent in 11 (31%). Given these results, recombinant (r) IL-2 was tested for its capacity to stimulate or enhance IFN-gamma production. rIL-2 (10 U/ml) alone stimulated cells from controls, ARC, and AIDS patients to secrete 93 +/- 25, 99 +/- 33, and 7 +/- 3 U/ml of IFN-gamma, respectively. rIL 2 (10 U/ml) plus antigen induced no change in mean IFN-gamma levels for controls, a 4.4-fold increase for 17 AIDS patients (16 +/- 16 vs. 71 +/- 21 U/ml), and a 7.2-fold increase (18 +/- 5 vs. 130 +/- 27 U/ml) for 19 ARC patients with abnormal IFN-gamma generation to antigen alone. Individual responses indicated that six of the 17 (35%) AIDS patients with opportunistic infections and 12 of the 19 (63%) with ARC were apparent responders to 10-100 U/ml of rIL-2. These results (a) document profound impairment in antigen-induced IL-2 secretion by AIDS and ARC T cells, (b) indicate that, in vitro, mononuclear cells from certain patients can respond to rIL-2 with enhanced IFN-gamma production, and thus (c) suggest that in selected patients rIL-2 might have a potentially beneficial therapeutic (AIDS) or prophylactic (ARC) effect against opportunistic infections.

Authors

H W Murray, K Welte, J L Jacobs, B Y Rubin, R Mertelsmann, R B Roberts

Polymorphism of the complement receptor for C3bi.

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Abstract

RM2.184, a mouse IgG2a monoclonal antibody, recognizes a polymorphic determinant on the complement receptor for C3bi which is present on granulocytes and monocytes. The RM2.184 epitope is distinct from the monomorphic determinant recognized by the monoclonal antibody OKM1. The RM2.184 epitope is probably on the alpha subunit and dependent on the association of the alpha and beta subunits for its configuration, as it can not be detected after the subunits have been dissociated. The phenotypic frequency of the RM2.184 antigen is approximately 14%, and its segregation in families is independent of HLA and consistent with an autosomal co-dominant mode of inheritance.

Authors

G R Russ, A P Haddad, B D Tait, A J d'Apice

Effect of hydrogen peroxide exposure on normal human erythrocyte deformability, morphology, surface characteristics, and spectrin-hemoglobin cross-linking.

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Abstract

To further define the conditions for forming spectrin-hemoglobin cross-linking in human erythrocyte membranes and to examine its possible effects on membrane function, we incubated normal human erythrocytes for up to 3 h in concentrations of H2O2, varying from 45 to 180 microM, in an azide phosphate buffer, pH 7.4. The chemical changes observed indicated that methemoglobin formation occurred early and at a low concentration (45 microM). Morphologic changes characterized by increased echinocyte formation occurred in a dose-dependent fashion. In addition, decreased cell deformability commensurate with increased membrane rigidity was found. Finally, an increase in cell recognition as determined by monocyte phagocytosis and adherence in vitro, as well as decreased phosphatidylcholine accessibility to bee venom phospholipase A2, was found in H2O2-treated erythrocytes compared with controls. Both of these latter changes were closely correlated with the extent of spectrin-hemoglobin cross-linking. In addition to these protein-mediated interactions, lipid peroxidation also occurred after H2O2 exposure, as shown by generation of fluorescent amino propene derivatives. The addition of the antioxidant, butylated hydroxytoluene, decreased the fluorescent derivatives, but did not prevent the effects on membrane function. This suggests that lipid peroxidation, though present, was not necessary for the membrane changes found. In contrast, spectrin-hemoglobin aggregation and the alterations in membrane function were completely prevented by prior exposure of the erythrocytes to carbon monoxide.

Authors

L M Snyder, N L Fortier, J Trainor, J Jacobs, L Leb, B Lubin, D Chiu, S Shohet, N Mohandas

A monoclonal antibody against basal cells of human epidermis. Potential use in the diagnosis of cervical neoplasia.

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Abstract

A murine monoclonal antibody was generated against human skin cells obtained from psoriatic plaques. The antibody, called VM-2, recognizes an epitope expressed on the basal cell layer of human skin and other epithelia. VM-2 also binds to cultured cells from a variety of human carcinomas including HeLa cervical carcinoma, A-431 vulvar carcinoma, A-549 lung alveolar carcinoma, and SCL-1 skin squamous cell carcinoma cells. In several primary human cell lines, including fibroblasts, endothelial cells, and cells from the hematopoietic lineage, the antigenic site recognized by VM-2 could not be detected. The cellular antigen when immunoprecipitated by VM-2 from both normal and transformed cells appears to be proteins of approximately 100,000 and 120,000 mol weight. In frozen sections from human tumor-containing tissues, VM-2 labels skin, cervical, and lung squamous carcinoma cells, as well as skin basal carcinoma cells. Malignant cells present in exfoliative smears from epidermoid invasive neoplasias of the cervix are also selectively recognized by VM-2 in distinction to normal squamous cervical cells. VM-2 is thus directed against an antigen associated with neoplastic cells when applied in selected sites of exfoliative cytology. This monoclonal antibody represents a new reagent that should prove useful in the diagnosis of cervical neoplasia.

Authors

V B Morhenn, A B Schreiber, O Soriero, W McMillan, A C Allison

Isolation and characterization of glycosaminoglycans in human plasma.

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Abstract

We have described methodology for the isolation and quantitation of glycosaminoglycans present in human plasma. Plasma glycosaminoglycans can be quantitatively adsorbed on a DEAE-Sephacel ion exchanger and eluted with a salt gradient as two groups: a low-charge fraction and a high-charge fraction. The low-charge fraction consists of chondroitin sulfate with a low sulfate content and the high-charge fraction consists of heparan sulfate, chondroitin sulfate, and keratan sulfate (type I). We have determined the plasma concentration of each of these glycosaminoglycans in six normal human subjects. We have established that none of the glycosaminoglycans in plasma are covalently linked to plasma proteins. All are isolated as complexes with plasma proteins in noncovalent linkages. The glycosaminoglycans in the low-charge fraction are bound with high affinity to a single plasma glycoprotein by a lectin-type bond that can be disrupted by a simple glycoside. The high-charge fraction contains three major proteins and several minor proteins associated with the glycosaminoglycans by both lectin-type and ionic bonding. The plasma proteins associated with glycosaminoglycans represent less than 0.5% of the total plasma proteins. Little is known about the physiologic role of the plasma glycosaminoglycans as components of metabolic processes. Because glycosaminoglycans have been implicated in lipid metabolism and atherosclerosis, we tested all of these compounds, isolated in free form, on the in vitro hydrolysis of triglycerides by lipoprotein lipase. Plasma heparan sulfate stimulated the rate of this reaction severalfold. All other plasma glycosaminoglycans were inactive. Thus, plasma heparan sulfate may play an important role in plasma lipoprotein metabolism.

Authors

I Staprans, J M Felts

Pathogenesis of heterogeneity in human multinodular goiter. A study on growth and function of thyroid tissue transplanted onto nude mice.

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Abstract

Functional and morphologic heterogeneity of human multinodular goiters was investigated in 300 samples from "cold" and "hot" regions of 20 goiters transplanted onto nude mice. Transplants were labeled with [3H]thymidine and radioiodine, while the host's thyroid-stimulating hormone (TSH) secretion was either stimulated or suppressed. Proliferation and function of follicular cells were assessed in whole follicles reconstructed from autoradiographs of serial sections. Hot transplants had a higher autonomous iodine uptake than those of cold tissue in TSH-suppressed hosts. Functional autonomy widely varied among the follicles, but even more so among individual cells. Hot grafts differed from cold ones only by a comparatively larger fraction of autonomous cells. Intercellular differences of iodinating activity were not abolished by TSH. Grafts faithfully reproduced the individual growth pattern of the original tissue. Between 0.5% and 7% of all follicular cells replicated despite suppression of TSH. Up to 70% of these cells were clustered, forming scattered foci of autonomously growing tissue. Other cells only started replicating after long-term TSH stimulation. Thus, goiters contained subsets of cells with high and others with low growth response. Progenies of replicating cells remained clustered, sometimes budding outwards to form new follicles. Autonomy of growth and autonomy of function are independent traits of epithelial cells. Epithelial cells have their individual growth pattern, replication rate, and functional capacity. These traits are passed on from a mother cell to its progeny during follicle neogenesis. To this main mechanism accounting for the morphologic and functional heterogeneity of human goiters, inheritable modifications of gene expression must probably be added.

Authors

H J Peter, H Gerber, H Studer, S Smeds

Interleukin 1 acts on cultured human vascular endothelium to increase the adhesion of polymorphonuclear leukocytes, monocytes, and related leukocyte cell lines.

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Abstract

Increased leukocyte adhesion to the endothelial lining of blood vessels is an essential event in inflammation and the pathogenesis of certain vascular diseases. We have studied the effect of interleukin 1 (IL-1), an inflammatory/immune mediator, on endothelial-leukocyte adhesion using quantitative in vitro assays. Selective pretreatment of cultured human umbilical vein endothelial monolayers with IL-1 (5 U/ml, 4 h) resulted in an 18.3 +/- 2.6-fold increase in human peripheral blood polymorphonuclear leukocyte (PMN) adhesion (mean +/- SEM, n = 16) and a 2.6 +/- 0.3-fold increase in monocyte adhesion (n = 7) over basal levels. IL-1-treated endothelial monolayers also supported increased adhesion of the promyelocytic cell line HL-60 and the monocytelike cell line U937 (33.0 +/- 6.0-fold, n = 6 and 4.9 +/- 0.5-fold, n = 15, respectively). In contrast, selective IL-1 pretreatment of leukocytes, or the addition of IL-1 during the adhesion assay, did not alter endothelial-leukocyte adhesion. Conditioned medium from IL-1-treated endothelial cultures also did not promote leukocyte adhesion to untreated monolayers. IL-1 induction of endothelial adhesivity was concentration dependent (maximum, 10 U/ml), time dependent (peak, 4-6 h), and reversible, was blocked by cycloheximide (10 micrograms/ml) or actinomycin D (5 micrograms/ml) but not by acetylsalicylic acid (100 microM), and occurred without detectable endothelial cell damage. IL-1 treatment of SV40-transformed human endothelial cells and dermal fibroblasts did not increase their adhesivity for leukocytes. These data suggest that IL-1 can act selectively on human vascular endothelium to increase its adhesivity for circulating blood leukocytes, and thus to localize leukocyte-vessel wall interactions at sites of inflammation in vivo.

Authors

M P Bevilacqua, J S Pober, M E Wheeler, R S Cotran, M A Gimbrone Jr

Defective binding and function of 1,25-dihydroxyvitamin D3 receptors in peripheral mononuclear cells of patients with end-organ resistance to 1,25-dihydroxyvitamin D.

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Abstract

Lectin-induced DNA synthesis by peripheral mononuclear cells from 17 normal donors was inhibited (40-60%) by 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) at physiological concentrations (10(-10)-10(-9) M). The lymphocytes acquire specific receptors for 1,25(OH)2D3 upon activation by the lectins. This process precedes the inhibitory effect of 1,25(OH)2D3. We studied lymphocytes from six patients from four different kindreds with the syndrome of hereditary end-organ resistance to 1,25(OH)2D (the so-called vitamin D-dependent rickets type II). In five patients (three kindreds) peripheral blood mononuclear cells did not acquire receptors for 1,25(OH)2D3 upon phytohemagglutinin-induced activation. Moreover, in contrast to normal lymphocytes, the mitogenic stimulation of these patients' lymphocytes by phytohemagglutinin and concanavalin A was not inhibited by 1,25(OH)2D3. Activated lymphocytes of the sixth patient from a fourth kindred exhibited normal binding of [3H]1,25(OH)2D3 but the hormone failed to inhibit the mitogenic stimulation. A similar pattern of the vitamin D effector system was previously observed in fibroblasts cultured from skin biopsies of the same group of patients. The conclusions from these findings are: (a) the inhibition of mitogenic stimulation by 1,25(OH)2D3 is mediated by specific functional receptors to the hormone; and (b) the receptors for 1,25(OH)2D3 in mononuclear cells are probably controlled genetically by the same mechanisms as the effector system in well-characterized target organs of the hormone, such as intestine and kidney.

Authors

R Koren, A Ravid, U A Liberman, Z Hochberg, Y Weisman, A Novogrodsky

Human transforming growth factor-alpha stimulates bone resorption in vitro.

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Abstract

Tumor-derived transforming growth factors (TGF) have been proposed as possible mediators of hypercalcemia in malignancy. We have studied the action of recombinant human TGF-alpha in cultured bone cells and in bone explant cultures. In clonal UMR-106 rat osteosarcoma cells, TGF-alpha and epidermal growth factor (EGF) were equipotent in binding to the EGF receptor. TGF-alpha and EGF both stimulated resorption of neonatal mouse calvaria, and maximal responses were obtained with 10 ng/ml of TGF-alpha after 72 h in culture. The effects of both TGF-alpha and EGF in calvaria, but not those of parathyroid hormone, were inhibited by 5 X 10(-7) M indomethacin. Fetal rat limb bone cultures were less sensitive to TGF-alpha than neonatal mouse calvaria, with a concentration of 30 ng/ml being required to stimulate resorption in this system. The bone-resorbing activity of TGF-alpha in fetal rat bones was inhibited by 10 ng/ml calcitonin but not by 5 X 10(-7) M indomethacin. EGF at concentrations up to 300 ng/ml did not stimulate resorption of the limb bones at time periods up to 66 h. The results indicate that human TGF-alpha is a potent bone-resorbing agent, and support the concept that this growth factor exhibits some effects distinct from those of EGF. TGF-alpha could play an etiologic role in the hypercalcemia of malignancy.

Authors

P H Stern, N S Krieger, R A Nissenson, R D Williams, M E Winkler, R Derynck, G J Strewler

Immunoglobulin G is a platelet alpha granule-secreted protein.

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Abstract

It has been known for 27 yr that blood platelets contain IgG, yet its subcellular location and significance have never been clearly determined. In these studies, the location of IgG within human platelets was investigated by immunocytochemical techniques and by the response of platelet IgG to agents that cause platelet secretion. Using frozen thin-sections of platelets and an immunogold probe, IgG was located within the alpha-granules. Thrombin stimulation caused parallel secretion of platelet IgG and two known alpha-granule proteins, platelet factor 4 and beta-thromboglobulin, beginning at 0.02 U/ml and reaching 100% at 0.5 U/ml. Thrombin-induced secretion of all three proteins was inhibited by prostaglandin E1 and dibutyryl-cyclic AMP. Calcium ionophore A23187 also caused parallel secretion of all three proteins, whereas ADP caused virtually no secretion of any of the three. From these data and a review of the literature, we hypothesize that plasma IgG is taken up by megakaryocytes and delivered to the alpha-granules, where it is stored for later secretion by mature platelets.

Authors

J N George, S Saucerman, S P Levine, L K Knieriem, D F Bainton

Immunoreactive corticotropin-releasing factor in human plasma.

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Abstract

Plasma immunoreactive corticotropin-releasing factor (I-CRF) levels were determined by using a human CRF radioimmunoassay and an immunoaffinity procedure. The basal plasma I-CRF level in normal subjects was 6 +/- 0.5 pg/ml (mean +/- SD). We found that most plasma I-CRF levels were affected by stress, negative feedback, and circadian rhythm. Basal I-CRF levels were high in patients with Addison's disease, Nelson's syndrome, hypopituitarism stemming from pituitary macroadenoma, and CRF- and adrenocorticotropic hormone-producing tumors. A very low, but significant, amount of I-CRF was detected (1-3 pg/ml) in patients with Cushing's syndrome, in corticosteroid-treated patients, and in a patient with hypothalamic hypopituitarism. These results suggest that a major component of plasma I-CRF is of hypothalamic origin, however, other extrahypothalamic tissues cannot be ruled out as a minor source of plasma I-CRF.

Authors

T Suda, N Tomori, F Yajima, T Sumitomo, Y Nakagami, T Ushiyama, H Demura, K Shizume

The transmembrane pH gradient drives uphill folate transport in rabbit jejunum. Direct evidence for folate/hydroxyl exchange in brush border membrane vesicles.

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Abstract

In rabbit jejunal, but not ileal brush border membrane vesicles, an outwardly directed OH- gradient (pH 7.7 inside, pH 5.5 outside) markedly stimulated the initial velocity of folate (0.1 microM) uptake compared with uptake in the absence of a pH gradient. Under pH gradient conditions, folate was transiently accumulated at a concentration four times that found at equilibrium (over-shoot), implying uphill transport of the vitamin. Equilibrium folate uptake was inversely proportional to medium osmolality, suggesting uptake into an osmotically sensitive space. pH gradient-stimulated folate uptake was markedly reduced by inhibitors of anion exchange (4,4'-diisothiocyano-2,2'-disulfonic acid stilbene; 4-acetamido-4-isothiocyanostilbene-2,2'-disulfonic acid; furosemide), and was saturable (folate Km = 0.19 +/- 0.02 microM; Vmax = 12.8 +/- 0.4 pmol X mg protein-1 X min-1). Imposition of an inside-positive electrical potential did not stimulate folate uptake, suggesting that stimulation by a pH gradient was not due to an induced electrical potential. In contrast, an inwardly directed Na+ or K+ gradient did not stimulate folate uptake. These findings provide evidence for a carrier on the jejunal brush border membrane that mediates folate/OH- exchange (or H+/folate co-transport), and are consonant with the known presence of an outwardly directed OH- gradient in vivo (brush border acid microclimate), an acidic pH optimum for intestinal folate uptake, and the primary role of the jejunum in folate absorption.

Authors

C M Schron, C Washington Jr, B L Blitzer