Elevated Thromboxane Levels in the Rat during Endotoxic Shock: PROTECTIVE EFFECTS OF IMIDAZOLE, 13-AZAPROSTANOIC ACID, OR ESSENTIAL FATTY ACID DEFICIENCY

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Abstract

The potential deleterious role of the proaggregatory vasoconstrictor, thromboxane A2, in endotoxic shock was investigated in rats. Plasma thromboxane A2 was determined by radioimmunoassay of its stable metabolite thromboxane B2. After intravenous administration of Salmonella enteritidis endotoxin (20 mg/kg), plasma thromboxane B2 levels increased from nondetectable levels (<375 pg/ml) in normal control rats to 2,054±524 pg/ml (n = 8), within 30 min to 2,071±429 at 60 min, and decreased to 1,119±319 pg/ml, at 120 min. Plasma levels of prostaglandin E also increased from 146±33 pg/ml in normal controls (n = 5) to 2,161±606 pg/ml 30 min after endotoxin (n = 5).

Authors

J. A. Cook, W. C. Wise, P. V. Halushka

Regulation of Calcitonin Secretion in Normal Man by Changes of Serum Calcium within the Physiologic Range

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Abstract

To examine the relative importance of calcium and gastrin in regulation of calcitonin secretion, we administered graded oral doses of calcium to 10 normal men, ages 23-29 yr. Each subject had previously shown an appropriate increase in calcitonin secretion in response to a pharmacologic (0.5 μg/kg) pentagastrin injection. On separate days and in random order, each man drank 250 ml of distilled water containing 0.0, 0.5, 1.5, and 3.0 g of elemental calcium as the gluconate salt. Blood samples were drawn before and at 30, 60, 90, 120, 180, and 240 min after the oral calcium dose. The samples were analyzed for calcium by atomic absorption spectroscopy, and for gastrin and calcitonin by radioimmunoassays of established sensitivity and specificity. Ingestion of water (control) caused no change in any of the three variables. Calcium ingestion resulted in dose-related increases, within the normal range, of all three variables. Immunoreactive gastrin rose promptly, peaking at 30 min, and returning to basal levels or below by 120 min. In contrast, calcium and immunoreactive calcitonin levels rose slowly and in parallel, peaking at 120-240 min. Changes in calcitonin and changes in calcium were strongly and positively correlated, r = 0.73, when all data were pooled. Furthermore, individual linear regressions for changes in calcitonin and calcium levels (calculated separately for the three oral calcium doses in each subject) had positive slopes in 28 out of 30 sets (P < 0.01). The changes in calcitonin concentrations were much more poorly correlated with the corresponding changes in serum gastrin levels; in fact, the regression coefficient was weakly negative, r = −0.20. These results show that, at least in young adult men, changes of ambient calcium concentration within the normal range may be of major importance in physiologic regulation of calcitonin secretion. The findings are consistent with the hypothesis that calcitonin functions to prevent excessive postprandial hypercalcemia.

Authors

Lynn A. Austin, Hunter Heath III, Vay Liang W. Go

Antigenic Modulation and Turnover in Human Neutrophils

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Abstract

Turnover of membrane constituents appears important in many biologic processes. We studied this process in neutrophils by immunologic methods. The capacity of neutrophils to recognize other neutrophils coated with antibodies against membrane antigens was used to determine the changes that occur after attachment of the antibody to the neutrophil membrane. Neutrophils were sensitized for 30 min at 22°C with antibodies from three patients with antineutrophil autoantibodies. The sensitized neutrophils were recognized by normal neutrophils, which responded with an increase in glucose oxidation. If, after sensitization, the sensitized neutrophils were not immediately exposed to normal neutrophils, but instead were incubated at 37°C for varying times, the capacity to elicit a recognition response decayed and was gone by 30 min. Additionally, the capacity of the cells to be resensitized by reexposure to antibody also decayed during this period. However, after further incubation at 37°C, the neutrophils recovered the capacity to become sensitized; and this recovery was not inhibited by the addition of cycloheximide. Control incubations with normal immunoglobulin (Ig)G did not elicit a recognition response. The decay in recognition response was temperature dependent. Direct immunofluorescent studies with fluorescein-conjugated antineutrophil IgG revealed that the antibodies were cleared by aggregation and endocytosis. We conclude that: (a) neutrophils clear antibody from the cell surface by a temperature-dependent mechanism; (b) antigenicity is cleared concomitantly; (c) the mechanism of clearance involves internalization; and (d) with time, antigenicity reappears on the cell surface.

Authors

Sigmund A. Weitzman, Mary C. Desmond, Thomas P. Stossel

Delayed-Type Hypersensitivity Skin Reactions in Congenital Afibrinogenemia Lack Fibrin Deposition and Induration

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Abstract

Induration is a characteristic feature of delayed-type hypersensitivity skin reactions and is the usual measure of their intensity. The precise basis of induration has not been established, although activation of the clotting system with consequent fibrin deposition has been clearly implicated. In this study, two subjects with congenital afibrinogenemia, a genetic defect in fibrinogen synthesis, were skin tested with standard microbial antigens: streptokinase-streptodornase, monilia, mumps, and tuberculin purified protein derivative. One positive delayed reaction from each subject was biopsied at 40-48 h and compared with 23 biopsies of similar skin tests in normal volunteers.

Authors

Robert B. Colvin, Michael W. Mosesson, Harold F. Dvorak

Recovery of Endothelial Cell Prostacyclin Production after Inhibition by Low Doses of Aspirin

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Abstract

Endothelial cells synthesize prostacyclin (PGI2), an unstable prostaglandin that inhibits platelet aggregation and serotonin release. Because cyclooxygenase, which is necessary for synthesis of PGI2, is inactivated by aspirin, we examined the effect of aspirin on PGI2 production by cultured human endothelial cells. Endothelial cells synthesize PGI2 (20.1±7.2 ng/106 cells, mean±SD) when stimulated with 20 μM sodium arachidonate for 2 min. PGI2 production is inhibited by low-dose aspirin (5 μM); the t½ of inactivation is 6.0±1.3 min (mean±SEM, n = 3). Thus, endothelial cell cyclooxygenase is as sensitive to aspirin as the enzyme in platelets. After 1 h incubation with aspirin, endothelial cell PGI2 production was inhibited 50% by 2.1±0.4 μM aspirin and was inhibited 90% by 6.2±0.9 μM aspirin (mean±SEM, n = 4). When endothelial cells were incubated with 100 μM aspirin, washed, and recultured, their ability to synthesize PGI2 returned to control levels in 35.6±1.0 h (mean±SEM, n = 4). Recovery of endothelial PGI2 production after aspirin depended on de novo protein synthesis because treatment with cycloheximide (3 μg/ml) inhibited recovery by 92%.

Authors

Eric A. Jaffe, Babette B. Weksler

Suppressor-Cell Antibody in Systemic Lupus Erythematosus: POSSIBLE MECHANISM FOR SUPPRESSOR-CELL DYSFUNCTION

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Abstract

Circulating antibodies that could be responsible for the suppressor thymus-derived (T)-cell dysfunction in active systemic lupus erythematosus (SLE) were investigated. Sera from 14 active and inactive SLE patients were compared with a pool of 22 normal sera. All sera were adsorbed with a pool of normal platelets to exclude antihistocompatibility leukocyte antigen antibodies; with AB erythrocytes to exclude isohemagglutinins; and with a pool of normal bone marrow-derived (B) lymphocytes, monocytes, and neutrophils to deplete anti-B-cell antibodies, Fc-receptor antibodies, and antibodies directed against neutrophils or monocytes. Sera from active SLE patients were capable of inhibiting the activation of normal, blood lymphocytes by concanavalin A to become suppressor cells. The latter were assayed by coculturing the concanavalin A-activated cells with autologous lymphocytes, which were then activated with either phytohemagglutinin for proliferative response or with pokeweed mitogen for B-cell immunoglobulin (Ig) synthesis and secretion. Specific incorporation of cultures with phytohemagglutinin showed a value of 67±13 (mean±SD) for suppressor cells treated with adsorbed, active SLE sera. This value was significantly different (P < 0.001) from that of cells treated with the inactive SLE sera or with the pool of normal sera. Similar findings were seen with respect to the B-cell target parameters. Cytoplasmic Ig and IgG in supernates of cultures with pokeweed mitogen showed values of 17±5% and 717±134 ng/culture, respectively, for suppressor cells treated with the adsorbed, active SLE sera. This was significantly different from those treated with the inactive SLE sera or with the pool of normal sera. The antisuppressor-cell factor was shown to be IgG, complement independent, not cytotoxic, active at 37°C and at room temperature, but not at 4°C, and adsorbable with T cells.

Authors

Akira Sagawa, Nabih I. Abdou

Platelet and Blood Vessel Arachidonate Metabolism and Interactions

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Abstract

Exogenous arachidonate addition to intact platelets, in the absence or the presence of blood vessel microsomes, results in the production of thromboxane B2 (the stable degradation product of thromboxane A2) only. Prostaglandin (PG) endoperoxides are released from intact platelets only when thromboxane synthetase is inhibited. Thus, addition of exogenous arachidonate to imidazole-pretreated platelets in the presence of bovine aorta microsomes (source of prostacyclin synthetase) results predominantly in the synthesis of 6-keto-PGF1α (the stable degradation product of prostacyclin). Strips of intact aorta were removed from aspirin-treated rabbits, thus the isolated blood vessels were unable to convert endogenous or exogenous arachidonate to prostacyclin. Human platelets, with [14C]arachidonate-labeled phospholipids, adhered to the blood vessel segments and released some thromboxane B2. The subsequent addition of thrombin facilitated the release of endogenous arachidonate and thromboxane, but no labeled 6-keto-PGF1α was detectable. There is therefore no direct chemical evidence of PG-endoperoxide release from human platelets during either aggregation or adhesion, which therefore precludes the possibility that blood vessels use platelet PG-endoperoxide for prostacyclin synthesis. Imidazole inhibited the thromboxane synthetase in the labeled platelets, and thereafter thrombin stimulation resulted in the release of platelet-derived, labeled PG-endoperoxides that were converted to labeled prostacyclin by the vascular prostacyclin synthetase. The latter result suggests a potential antithrombotic therapeutic benefit might be achieved using an effective thromboxane synthetase inhibitor.

Authors

Philip Needleman, Angela Wyche, Amiram Raz

Lymphocyte Adherence in Multiple Sclerosis: EFFECT OF ASPIRIN

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Abstract

Peripheral blood lymphocytes from multiple sclerosis (MS) patients form substantially greater numbers of rosettes with measles virus-infected human epithelial cells than do lymphocytes from healthy controls or from patients with other diseases. We have previously shown that prostaglandin E1-treated normal lymphocytes exhibit increased lymphocyte adherence, and thus behave like MS lymphocytes in this in vitro system. In this study we describe the effect of prostaglandin synthesis inhibition on lymphocyte adherence in both MS and control patients. Direct addition of aspirin or indomethacin to peripheral blood mononuclear cells from MS patients in vitro reduced lymphocyte adherence to control levels. Ingestion of therapeutic (anti-inflammatory) doses of aspirin (1 g, 4 times daily for 2 d) by MS patients resulted in reduction of lymphocyte adherence to levels seen in healthy controls. A single 325-mg dose of aspirin did not reduce lymphocyte adherence. A dose-dependent reduction in lymphocyte adherence was observed after single doses ranging from 650 mg to 1.3 g; duration of the effect was directly related to the aspirin dose. These observations indicate that treatment of MS patients with aspirin profoundly influences adherence of their lymphocytes to measles virus-infected cells and suggest that the altered cellular response, which results in increased lymphocyte adherence in MS patients, may be mediated by a prostaglandin-sensitive mechanism.

Authors

Paula Dore-Duffy, Robert B. Zurier

Thrombogenic Effect of High-Dose Aspirin in Rabbits: RELATIONSHIP TO INHIBITION OF VESSEL WALL SYNTHESIS OF PROSTAGLANDIN I₂-LIKE ACTIVITY

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Abstract

Aspirin is a promising antithrombogenic agent. It inhibits the generation of thromboxane A2 by acetylating platelet cyclo-oxygenase. Aspirin also inhibits vessel wall production of PGI2 which is an inhibitor of platelet aggregation, and therefore is potentially thrombotic. To investigate these two opposing effects we studied the effects of aspirin upon fibrin accretion onto experimentally induced venous thrombi in rabbits and on the PGI2-like activity of vessel wall using the thrombin-induced [14C]serotonin release assay. A 200-mg/kg dose of aspirin significantly augmented thrombus size when compared to (a) sodium salicylate administered in equal doses, (b) aspirin in a 10-mg/kg dose or (c) controls (P < 0.001). A 200-mg/kg dose of aspirin totally inhibited vessel wall PGI2-like activity whereas aspirin in a 10-mg/kg dose produced less inhibition, and 200 mg/kg sodium salicylate had no effect. Local instillation of tranylcypromine, an inhibitor of PGI2 formation, also significantly augmented thrombus size compared to saline-treated controls and totally inhibited the production of PGI2-like activity. The thrombogenic effect of high dose aspirin was lost if an interval of 2.5 h or longer elapsed between vessel damage and drug administration, indicating that in contrast to the platelet, the effect of aspirin on vessel wall prostaglandin synthesis is relatively short-lived. It is concluded that aspirin, in doses higher than those used clinically, can augment experimental thrombosis, presumably by inhibiting the synthesis of vessel wall PGI2.

Authors

J. G. Kelton, J. Hirsh, C. J. Carter, M. R. Buchanan

Glucose Disposal during Insulinopenia in Somatostatin-Treated Dogs: THE ROLES OF GLUCOSE AND GLUCAGON

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Abstract

The first aim of this study was to determine whether the plasma glucose level can regulate hepatic glucose balance in vivo independent of its effects on insulin and glucagon secretion. To accomplish this, glucose was infused into conscious dogs whose basal insulin and glucagon secretion had been replaced by exogenous intraportal insulin and glucagon infusion after somatostatin inhibition of endogenous pancreatic hormone release. The acute induction of hyperglycemia (mean increment of 121 mg/dl) in the presence of basal levels of insulin (7±1 μU/ml) and glucagon (76±3 pg/ml) resulted in a 56% decrease in net hepatic glucose production but did not cause net hepatic glucose uptake.

Authors

Gerald I. Shulman, John E. Liljenquist, Phillip E. Williams, William W. Lacy, Alan D. Cherrington