Collagen synthesis in normal and osteoarthritic human cartilage.

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Abstract

Collagen metabolism in osteoarthritic human articular cartilage was compared to that in normal cartilage and was also correlated with the degree of severity of the osteoarthritic lesion as determined by a histological-histochemical grading system. No correlation was apparent between the concentrations of DNA, hydroxyproline, and hydroxylysine and the degree of severity of the osteoarthritic lesion (except in far-advanced lesions). Similarly, there was no correlation in levels of these components in tissues from the normal vs. osteoarthritic group. The similarity of the values of the ratio hydroxylysine/hydroxyproline in osteoarthritic tissue compared with normal, and the lack of variation in these with increasing severity of the disease process argues against the possibility that osteoarthritis is associated with a major shift in the synthesis of type II collagen to type I. [3H]Proline incorporation into osteoarthritic cartilage was increased fourfold as compared to normal cartilage and varied with advancing histological-histochemical grade. Measurement of the specific activity of insolubilized hydroxyproline-containing material of the cartilage matrix, as an index of the turnover of collagen, showed a sixfold increase in osteoarthritic cartilage which also varied with grade. These data suggest that collagen synthesis in these tissues is substantially greater than in nonosteoarthritic tissues and varies directly with the severity of the disease process up to a point and then varies inversely as the lesion becomes more severe.

Authors

L Lippiello, D Hall, H J Mankin

Effect of estrogen on post-heparin lipolytic activity. Selective decline in hepatic triglyceride lipase.

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Abstract

The rise in plasma triglyceride (TG) levels associated with estrogen administration has been thought to arise from impaired clearance because of the uniform suppression of post-heparin lipolytic activity (PHLA). Recently PHLA has been shown to consist of two activities: hepatic TG lipase and extrahepatic lipoprotein lipase (LPL). To determine whether estrogen might induce a selective decline in one of these activities, both hepatic TG lipase and extrahepatic LPL were measured in post-heparin plasma from 13 normal women before and after 2 wk of treatment with ethinyl estradiol (1 mug/kg per day). Hepatic TG lipase and extrahepatic LPL were determined by two techniques: (a) separation by heparin-Sepharose column chromatography, and (b) selective inhibition with specific antibodies to post-heparin hepatic TG lipase and milk LPL. Estrogen uniformly depressed hepatic TG lipase as measured by affinity column (-68 +/- 12%, mean +/- SD, P less than 0.001) or antibody inhibition (-63 +/- 11%, P less than 0.001). Extrahepatic LPL was not significantly changed by affinity column (-22 +/- 40%) or antibody inhibition (-3 +/- 42%). Direct measurement of adipose tissue LPL from buttock fat biopsies also showed no systematic change in the activated form of LPL measured as heparin-elutable LPL (+64 +/- 164%) or in the tissue form of LPL measured in extracts of acetone-ether powders (+21 +/- 77%). The change in hepatic TG lipase correlated with the change in PHLA (r = 0.969, P less than 0.01). However, neither the change in PHLA nor hepatic TG lipase correlated with the increase in TG during estrogen. The decrease in PHLA during estrogen thus results from a selective decline in hepatic TG lipase.

Authors

D M Applebaum, A P Goldberg, O J Pykälistö, J D Brunzell, W R Hazzard

Studies of the mechanism of contralateral polyuria after renal artery stenosis.

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Abstract

Acute renal artery stenosis in hydropenic dogs caused a contralateral increase in urine volume and free water clearance without change in glomerular filtration, renal blood flow, or osmolar clearance. The increase in urine volume was not dependent on the development of hypertension since it occurred in animals pretreated with trimethaphan but was dependent upon angiotensin since it was presented with angiotensin blockade with Saralasin. The effect was not caused by angiotensin inhibiting antidiuretic hormone release since the polyuria occurred in hypophysectomized animals receiving a constant infusion of 10 muU/kg per min of aqueous Pitressin. Since the rise in urine volume was associated with an increase in renal vein prostaglandin E concentration and was prevented by pretreatment with indomethacin (5 mg/kg) the results suggest that the rise in plasma angiotensin after renal artery stenosis causes an increase in contralateral prostaglandin E synthesis with resultant antagonism to antidiuretic hormone at the collecting tubule.

Authors

O G Galvez, B W Roberts, M H Mishkind, W H Bay, T F Ferris

A subpopulation of normal human peripheral B lymphcytes that bind IgE.

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Abstract

Isolated normal human peripheral lymphocytes were analyzed for their ability to bind IgE as shown by rosette formation with aldehydefixed ox red cells coated with an IgE myeloma protein (Eo'-IgE) as indicator cells. An average of 4.3% of the cells in the lymphocyte preparations of 12 donors formed Eo'-IgE rosettes. The lymphocyte preparations contained an average of 0.36% basophils which also formed Eo'-IgE' rosettes, suggestiing that about 4% of the lymphocytes bound IgE. The rosette formation was inhibited by IgE myeloma protiens or IgE Fc fragments but not by IgE Fab fragments or Ig of the other classes. On the average, the lymphocytes of the 12 donors contained 70.5% cells forming spontaneous rosettes with sheep erythrocytes (E), 10.6% cells having surface immunoglobulin (SIg), and 15.5% bunding IgG as shown by rosette formation with IgG-coated ox red cells (EoA). Fractionation of the lymphocytes into populations rich in spontaneously E-rosetting cells and cells with SIg indicated that the majority of the lymphocytes forming Eo'-IgE rosettes belonged to the SIg-positive lymphocytes. Analyses of lymphocyte populations lacking cells forming EoA rosettes and of rosetting with mixed indicator cells both demonstrated that over 90% of the lymphocytes forming Eo'-IgE rosettes did not form EoA rosettes and apparently had no Fc receptors for IgG. Pretreatment of the lymphocytes with trypsin in amounts that did not alter the number of EoA-rosetting cells abolished the Eo'-IgE rosette formation. These data indicate that a subpopulation of normal human peripheral lymphocytes, probably belonging to the B-cell type, binds IgE presumably via trypsin-sensitive receptors specific for the Fc fragment of IgE. The surface markers of these lymphocytes resemble those of cultured human lymphoblastoid cells that have recently been shown to bind IgE.

Authors

A Gonzalez-Molina, H L Spiegelberg

Treatment of aplastic anemia by marrow transplantation from HLA identical siblings. Prognostic factors associated with graft versus host disease and survival.

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Abstract

73 consecutive patients with severe aplastic anemia were treated by marrow transplantation from hematologically normal HLA identical siblings. 68 patients lived long enough to document marrow engraftment. 21 rejected the graft and 19 of these died. 47 sustained engraftment and 18 of these died. In 16 patients, death was associated with graft versus host disease. 29 patients with sustained engraftment are alive with complete hematologic restoration between 8 mo and 5 yr. This analysis, by using a proportional hazards regression model, was directed at identifying factors that predicted survival (and absence of graft versus host disease). Of the 24 factors entered into the analysis only two strongly correlated with survival: (a) sex match of donor and recipient (P less than 0.01), and (b) absence of refractoriness to random donor platelets at the time of transplantation (P less than 0.05). Refractoriness adversely influenced the survival of the sex mismatched patients, These data suggest that X and Y-associated transplantation antigen systems are important determinants of the outcome of marrow grafts between HLA identical siblings for the treatment of aplastic anemia. The machanism by which refractoriness to random donor platelets influences survival is currently unclear.

Authors

R Storb, R L Prentice, E D Thomas

Denatured hemoglobin in sickle erythrocytes.

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Abstract

To study the nature of numerous inclusion bodies seen in red cells from patients with sickle cell disease (Hb SS), we have prepared red cell ghosts free of oxyhemoglobin and analyzed them by spectrophotometric and heme extraction methods. The absorption spectrum in the visible region of the ghost suspensions was typical of hemichromes. The spectrum was similar to that of denatured hemoglobin repared by treatment of oxyhemoglobin S with mechanical shaking or heat. Similar treatment of cells containing only normal hemoglobin (Hb AA) showed a very small amount of denatured hemoglobin, approximately one-fifth of the amount in Hb SS cells. The amount of denatured hemoglobin determined after solution of membrane with 2.5% sodium dodecyl sulfate was 0.158+/-0.070% (1 SD) of the total cellular heme in Hb SS patients. In controls, the amount was 0.030+/-0.016%. Persons with Hb AA and reticulocytosis did not have an elevated amount of membrane-associated heme. In patients with hereditary spherocytosis and autoimmune hemolytic anemia, denatured stromal hemoglobin was normal or slightly elevated before and after splenectomy. The increased amount of denatured hemoglobin in Hb SS red cells may be related to the instability of sickle oxyhemoglobin.

Authors

T Asakura, K Minakata, K Adachi, M O Russell, E Schwartz

Platelet interaction with modified articular cartilage. Its possible relevance to joint repair.

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Abstract

During studies concerned with the platelet-collagen interaction, it was observed that platelets did not adhere to bovine or human articular cartilage and that cartilage did not induce platelet aggregation in vivo or in vitro. To study the mechanism responsible for this observation, the role of proteoglycans was examined. Purified cartilage collagen proved to be fully active as a platelet aggregant. Addition of small amounts of proteoglycan subunit (PGS) blocked platelet aggregation, whereas chondroitin sulfate, a major glycosaminoglycan component of cartilage matrix, impaired platelet aggregation only at concentrations which resulted in a marked increase in viscosity. Moreover, PGS abolished aggregation of platelets by polylysine but did not prevent aggregation by ADP, suggesting that PGS may block strategically placed lysine sites on the collagen molecule. Treatment of fresh articular cartilage with proteolytic enzymes rendered the tissue active as a platelet aggregant. In vivo experiments demonstrated that surgical scarification of rabbit articular cartilage does not result in adhesion of autologous platelets. Treatment of rabbit knee joints with intraarticular trypsin 1 wk before the injection of blood resulted in adhesion and aggregation of platelets on the surface of the lesions. Since there is evidence from other studies that some degree of cartilage healing may take place after initiation of an inflammatory response, it is postulated that induction of platelet-cartilage interaction may eventuate in cartilage repair.

Authors

D Zucker-Franklin, L Drosenberg

Postsynthetic deamidation of hemoglobin Providence (beta 82 Lys replaced by Asn, Asp) and its effect on oxygen transport.

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Abstract

Carriers of hemoglobin Providence have three types of beta chain in their hemolysates. The two abnormal chains have asparagine (Providence N, Prov N) or aspartic acid (Providence D) at position beta 82, instead of lysine. In vitro, only two beta chains are synthesized by reticulocytes of carriers, betaA and betaProv N. In vivo studies showed that the specific activity of Providence N was initially 10-fold higher than that of Providence D; the specific activities of the two labeled hemoglobins were approximately equal 5 wk after injection of isotope. Oxygen affinity of carriers' blood was somewhat increased, but they were not polycythemic. The affinity of the purified hemoglobins Providence was decreased. Addition of 2, 3 diphosphoglycerate had little effect on the affinity of either hemoglobin component, and addition of inositol hexaphosphate produced no change in the affinity of Providence D. These studies demonstrate that Providence N is deamidated to Providence D during the life span of the erythrocyte, and suggest this finding may represent only an easily observed prototype of posttranslational modification of proteins in general. Despite and abnormal P50 of the blood, oxygen transport is probably normal in carriers of the abnormal hemoglobins.

Authors

S Charache, J Fox, P McCurdy, H Kazazian Jr, R Winslow, P Hathaway, R van Beneden, M Jessop

Inhibition of thyroid-stimulating hormone stimulation of protein kinase, glucose oxidation, and phospholipid synthesis in thyroid slices previously exposed to the hormone.

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Abstract

Prior exposure of thyroid slices to thyrotropin (TSH) induced refractoriness to subsequent stimulation of the cyclic AMP system by the hormone. Although the inhibition is incomplete, we examined whether the reduction in cyclic AMP was sufficient to alter other metabolic effects of TSH. Bovine or dog thyroid slices were incubated with or without 5-100 mU/ml TSH for 1-2h, washed, and then incubated without hormone for 1-2h. Half of the slices not exposed to TSH initially were then incubated with buffer and half were exposed to 5-100 mU/ml TSH. Slices initially incubated with TSH were also incubated with or without TSH in the third incubation. During the refractory period, TSH activation of protein kinase was inhibited even though the hormone still caused some increase in cyclic AMP concentrations. However, protein kinase activity was fully responsive to dibutyryl cyclic AMP when slices were incubated with it during the third incubation. Stimulation of glucose oxidation by TSH was significantly decreased in thyroid slices previously incubated with the hormone. During refractoriness, stimulation of glucose oxidation caused by prostaglandin E1 and dibutyryl cyclic AMP was also significantly diminished but that due to acetylcholine was not. Thus even though dibutyryl cyclic AMP could fully activate protein kinase activity during refractoriness, its effect on glucose oxidation was still inhibited, suggesting that the metabolic block responsible for this refractoriness was distal to activation of protein kinase. Stimulation of 32Pi incorporation into phospholipid by TSH and acetylcholine was also inhibited during refractoriness. Despite reduction of the stimulatory effect of TSH, binding of 125ITSH was not modified by prior incubation of thyroid slices with TSH. These results indicate that changes in the TSH receptor are not responsible for the development of refractoriness and other metabolic sites besides activation of adenylate cyclase appear to be involved.

Authors

J B Field, G Bloom, C Chou, M E Kerins

Liver collagen synthesis in murine schistosomiasis.

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Abstract

Collagen synthesis was measured in liver slices obtained from mice with hepatosplenic schistosomiasis. Enlarged fibrotic livers from these mice contained 20 times more collagen than normal. This model of hepatic fibrosis results from an inflammatory granulomatous host response to Schistosoma mansoni ova in portal tracts, rather than from direct lover cell injury as with carbon tetrachloride-induced liver fibrosis. Collagen synthesis, as measured by the formation of labeled protein-bound hydroxyproline, occurred in granulomas isolated from fibrotic livers. Labeled collagen that cochromatographed with type I collagen was extracted with neutral salt solution from liver slices incubated with labeled proline. The free proline pool of the liver was doubled in infected mice; coordinately, liver slices from these animals showed maximal collagen production when the concentration of free proline in the medium was raised to 0.4 mM, the same level measured in the fibrotic livers. Under such conditions, collagen synthesis was at a rate equivalent to the formation of 5.4 nmol of protein-bound hydroxyproline per g liver in 6 h. In comparative incubations in medium containing 0.2 mM proline, fibrotic liver slices produced 16-fold more collagen than normal slices. The proline analogue, L-azetidine 2-carboxylic acid, effectively inhibited synthesis of labeled collagen by fibrotic liver slices. These studies show the synthesis of collagen in a reproducible animal model of the most prevalent form of human liver fibrosis. Difinitition of the controlling factors in this system is of interest for the general problem of fibrosis produced by immunological responses.

Authors

M A Dunn, M Rojkind, K S Warren, P K Hait, L Rifas, S Seifter

Mechanism of resistance to the phosphaturic effect of the parathyroid hormone in the hamster.

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Abstract

The effect of parathyroid hormone and calcitonin on the renal excretion of phosphate, calcium, and cyclic AMP was evaluated in the thyroparathyroidectomized hamster, a mammal apparently reisstant to the phosphaturic effect of parathyroid hormone. Parathyroid hormone did not increase phosphate excretion, although it decreased excretion of calcium and increased urinary excretion of cyclic AMP. This lack of a phosphaturic response to parathyroid hormone was not reversed by administration of 25-OH vitamin D or infusions of calcium or phosphate. Calcitonin, another potentially phosphaturic hormone, also vailed to increase phosphate excretion but markedly elevated urinary excretion of cyclic AMP. In hamsters pretreated with infusion of urinary ammonium chloride, which decreased plasma and urinary pH, both parathyroid hormone and calcitonin increased excretion of phosphate as well as that of cyclic AMP. Acetazolamide had no phosphaturic effect in ammonium chloride-loaded hamsters, and it decreased cyclic AMP and calcium excretion. Alkalinization of urine by acetazolamide did not prevent the phosphaturic effect of parathyroid hormone in ammonium chloride-loaded hamsters, but it blocked the increase in urinary cyclic AMP excretion. Parathyroid hormone and calcitonin both stimulated adenylate cyclase in a cell-free system (600-g pellet) from hamster renal cortex, elevated tissue cyclic AMP levels, and activated protein kinase in tissue slices from hamster renal cortex. In acid medium, the increase in cyclic AMP and activation of protein kinase in response to parathyroid hormone was diminished, but addition of acetazolamide restored responsiveness of both parameters to control values. Acetazolamide, on the other hand, did not influence adenylate cyclase or its response to parathyroid hormone or cyclic AMP phosphodiesterase activity. We conclude that the lack of a phosphaturic effect of parathyroid hormone and calcitonin in the hamster depends on steps in the cellular action of these hormones, steps that are sensitive to pH subsequent to cyclic AMP generation and protein kinase activation. In addition, acetazolamide may potentiate the phosphaturic effect of parathyroid hormone by promoting accumulation of cyclic AMP in tissue. Thus, the hamster is a particularly useful model for studies of syndromes in which there is renal resistance to phosphaturic hormones.

Authors

F G Knox, J Preiss, J K Kim, T P Dousa

Metabolism of vasoactive peptides by human endothelial cells in culture. Angiotensin I converting enzyme (kininase II) and angiotensinase.

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Abstract

Cultured endothelial cells provide a model for the study of interactions of vasoactive peptides with endothelium. Endothelial cell cultured from veins of human umbilical cords contain both angiotensin I converting enzyme (kininase II) and angiotensinase activities. Intact monolayers of cells can both activate angiotensin I and inactivate bradykinin when the peptides are added to culture flasks in protein-free medium. Intact suspended cells or lysed cells convert angiotensin I to angiotensin II, inactivate bradykinin, and hydrolyze hippuryldiglycine to hippuric acid and diglycine. These actions are inhibited by SQ 20881, the specific inhibitor of converting enzyme. The kininase activity of endothelial cells was partially inhibited by antibody to human lung converting enzyme. Endothelial cells also inactivate longer analogs of bradykinin, such as kallidin, methionyl-lysyl bradykinin, and bradykinin coupled covalently to 500,000 mol wt dextran. The endothelial cells retained converting enzyme activity through four successive subcultures, indicating that the enzyme is synthesized by the cells surface, and it is apparently a marker for endothelial cells, since cultured human fibroblasts, smooth muscle cells, and baby hamster kidney cells do not have it. Endothelial cells also contain an aminopheptidase which hydrolyzes both angiotensin II and the synthetic substrate, alpha-L-aspartyl beta-naphthylamide. The angiotensinase activity increased when the cells were lysed, which suggests that the enzyme is localized within the cells, Hydrolysis of both alpha-L-aspartyl beta-naphthylamide and angiotensin II was inhibited by omicron-phenanthroline, indicating that the enzyme is an A-tipe anigotensinase.

Authors

A R Johnson, E G Erdös

Relative contributions of large and small airways to flow limitation in normal subjects before and after atropine and isoproterenol.

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Abstract

Bronchodilatation was produced in normal subjects by the inhalation of atropine, a parasympatholytic agent, and isoproterenol, a beta adrenergic stimulator. Density dependence of maximal expiratory flow (Vmax), expressed as a ratio of Vmax with an 80% helium-20% oxygen gas mixture to Vmax with air at isolung volumes, indicated that the predominant flow regimes across upstream airways changed differently after each agent was given separately. After atropine Vmax increased, elastic recoil pressure did not change, and density dependence decreased. Utilizing the equal pressure points analysis which defines upstream and downstream segments of the intrathoracic airways at flow limitation, these results suggest a greater relative dilatation of the larger upstream airways such that more of the driving pressure is dissipated across the smaller airways in which flow is less dependent upon gas density. After isoproterenol Vmax increased, elastic recoil pressure did not change, and density dependence increased. This suggests a preferential dilatation of the smaller and more peripheral airways with less density-dependent flow regimes such that more of the driving pressure would be dissipated in the larger airways in which flow is more dependent upon gas density. Systematic decreases after isoproterenol lead independently to the same conclusion. After both agents together, Vmax increased and density dependence and critical alveolar pressures did not change from control, suggesting a relatively uniform dilatation of all the airways comprising the upstream segment.

Authors

R H Ingram Jr, J J Wellman, E R McFadden Jr, J Mead

Metabolism of the fifth component of complement, and its relation to metabolism of the third component, in patients with complement activation.

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Abstract

The metabolism of the fifth component of complement (C5), and its relatonship to metabolism of the third component of complement (C3), has been studied in normal subjects and patients by simultaneous administration of radioiodine labeled C5 and C3. In seven normal subjects the fractional catabolic rate of C5 ranged from 1.5 to 2.1% of the plasma pool/h and extravascular/intravascular distribution ratio from 0.22 to 0.78, these values being similar to those obtained for C3, and synthesis rate from 71 to 134 mug/kg per h, In patients with complement activation the increase in fractional catabolic rate of C5 was nearly always less than that of C3. The data also showed that there was increased extravascular distribution of C3 and C5 in most patients and considerable extravascular catabolism of both proteins in some. However, there were differences in metabolic parameters between patients with different types of complement activation. In patients with systemic lupus erythematosus, fractional catabolism and extravascular distribution of C3 and C5 were both increased, and there was marked extravascular catabolism of both proteins. There was increased fractional catabolism and extravascular distribution of C3 in patients with mesangiocapillary nephritis and (or) partial lipodystrophy, and fractional catabolism of C5 was also increased in three of six studies although distribution of C5 was always within the normal range; however, in two patients with nephritic factor in their serum fractional catabolism of C5 was normal despite markedly increased C3 turnover, suggesting that in patients with alternative pathway activation by nephritic factor little or no C5 convertase is generated.

Authors

J G Sissons, J Liebowitch, N Amos, D K Peters

Factors controlling gastric-glucagon release.

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Abstract

A system consisting of an isolated dog stomach perfused with whole blood has been designed to study gastric glucagon secretion. Under basal conditions, gastric glucagon release was 0.0-3.1 ng glucagon/100g of stomach per min. Arginine, at an arterial plasma concentration averaging 10 mM, elicited a rapid glucagon release. This gastric glucagon release was almost completely abolished by somatostatin (100 ng/ml). The release of gastric glucagon was not affected by hyperglycemia alone but was reduced by about 40% when hyperglycemia was concomitant with an hyperinsulinemia within the physiological range. These observations support the concept that adequate concentrations of insulin are necessary in order for hyperglycemia to inhibit gastric glucagon secretion. Furthermore, it is suggested that the isolated perfused dog stomach might provide a unique tool permitting investigation of alpha-cell function in the absence of endogenously released insulin.

Authors

P J Lefèbvre, A S Luyckx

Iodinating activity of thyroid tissue in toxic diffuse goiter.

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Abstract

Thyroid tissue obtained from 12 patients with Graves' disease and treated with thionamide drugs for 3-7 mo before subtotal thyroidectomy, from 12 patients with Graves' disease, similarly treated, and given 50 mug of triiodothyronine (T3) for 10 days before surgery, and from 12 euthyroid patients with solitary cold nodules was investigated to compare in vitro iodination of thyroglobulin in toxic diffuse goiter and in normal thyroid tissue. The supernates of the homogenates (105,000g) were subjected to sucrose density gradient centrifugation (5--28%) to separate the thyroglobulin fraction. The precipitates were treated with 1% digitonin and centrifuged to collect the supernate (particulate fraction). When thyroglobulin and particulate fractions obtained from the same patient were incubated with 125I-, iodide, glucose, and glucose oxidase, the amount of iodine bound to thyroglobulin was several times greater in toxic diffuse goiter than in normal thyroid tissue; administration of T3 did not affect iodination in toxic diffuse goiter. When the thyroglobulin fraction from each patient was incubated with a standardized quantity of peroxidase instead of the individual particulate fraction, the amount of iodine bound to thyroglobulin was the same among the three groups of patients. Finally, when bovine serum albumin was substituted for thyroglobulin from each of the patients, iodination of bovine serum albumin was several times greater with the particulate fraction obtained from toxic diffuse goiter tissue than with that obtained from normal tissue. The guaiacol-oxidizing activity oty. These results suggest that in vitro iodination of thyroglobulin is increased in toxic diffuse goiter even when patients are made euthyroid by treatment with thionamide drugs as well as when they are given additional T3 for 10 days before operation. The increase in iodination of thyroglobulin appears to be due to an increase in peroxidase activity in the particulate fraction.

Authors

S Nagataki, H Uchimura, H Ikeda, N Kuzuya, Y Masuyama

Adenylate cyclase of human fat cell ghosts. Stimulation of enzyme activity by parathyroid hormone.

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Abstract

Some of the effects of native bovine parathyroid hormone and of the synthetic aminoterminal 1-34 fragment on the adenylate cyclase activity of human fat cell ghosts were studied. Saturating concentrations of both hormone preparations caused a significant increase of enzyme activity by about 200-300%. Guanosine 5'-triphosphate (0.1 mM) inhibited basal enzyme activity but had no substantial effect on parathyroid hormone-stimulated enzyme activity. The guanosine 5'-triphosphate analogue, 5'-guanylyl-imidodiphosphate, produced about a threefold enhancement of basal and parathyroid hormone-stimulated enzyme activities under standard conditions (5 mM Mg+2, 1mM ATP, pH 8.0, 30 degrees C). Activation by parathyroid hormone was not influenced by beta-adrenergic blockade in contrast to stimulation by epinephrine. The sensitivity of the enzyme system to the native and the synthetic parathyroid hormone was, however, abolished after pretreatment of the fat cells with trypsin (1 mg/ml). The stimulatory effects of epinephrine and NaF were not affected by pretreatment with trypsin. The results suggest that human fat cells, like rat adipocytes, contain a multireceptor-coupled adenylate cyclase.

Authors

H Kather, B Simon