thromboxane-b2 and linsidomine

We compared the effects of L-arginine (L-ARG), the precursor of endogenous NO, on platelet aggregation and thromboxane A2 formation in vivo and in vitro. Human platelet-rich plasma (PRP) was anticoagulated with citrate (which decreases extracellular Ca2+) or with recombinant hirudin (which does not affect extracellular Ca2+). Two groups of 10 healthy male volunteers received intravenous infusions of L-ARG (30 g or 6 g, 30 min) or placebo. Blood was collected immediately before and at the end of the infusions for aggregation by ADP or collagen. Infusion of L-ARG inhibited ADP-induced aggregation in PRP anticoagulated with citrate by 37.5+/-6.3% (P < 0.05). In PRP anticoagulated with hirudin, aggregation was inhibited by 33.6+/-16.0% (P < 0.05). L-ARG infusion also inhibited platelet TXB2 formation and slightly, but not significantly decreased the urinary excretion rate of 2,3-dinor-TXB2; cGMP concentrations in PRP were significantly elevated during L-arginine infusion. In vitro preincubation with L-ARG (10 microM-2.5 mM) inhibited platelet aggregation in PRP anticoagulated with rhirudin, but not citrate. This effect was stereospecific for L-arginine, as D-arginine had no effect. It was dependent upon NO synthase activity, as indicated by increased cGMP levels in PRP. Moreover, both the NOS inhibitor L-NMMA and the inhibitor of soluble guanylyl cyclase ODQ antagonized the effects of L-ARG. Haemoglobin, an extracellular scavenger of NO, partly antagonized the antiplatelet effects of L-ARG. 8-Br-cyclic GMP and the exogenous NO donor linsidomine inhibited aggregation in PRP anticoagulated with citrate or r-hirudin. The inhibitory effects of L-ARG on platelet aggregation in vitro were paralleled by increased cyclic GMP levels; L-ARG also inhibited platelet TXB2 formation in PRP anticoagulated with r-hirudin, but not citrate. We conclude that the L-arginine/NO pathway is present in human platelets as a Ca2+-dependent anti-aggregatory pathway. In vivo the formation of NO from L-ARG by endothelial cells may contribute to the platelet-inhibitory effects of L-ARG. NO-releasing compounds like linsidomine inhibit platelet aggregation in vitro independent of extracellular Ca2+.

Topics: Adult; Antithrombins; Arginine; Blood Platelets; Cyclic GMP; Enzyme Inhibitors; Humans; In Vitro Techniques; Infusions, Intravenous; Male; Molsidomine; Nitric Oxide Synthase; Platelet Aggregation; Platelet Aggregation Inhibitors; Thromboxane A2; Thromboxane B2; Thromboxanes

Many lines of evidence indicate that an increased pancreatic production of nitric oxide (NO) and prostaglandins (PGs) is found in the pancreas of streptozotocin-diabetic rats and that endothelins (ETs) are closely related to the nitridergic and prostanoid pathway in several tissues. In the present study the relationship between NO, ETs, and PGs has been explored in isolated pancreatic tissue from streptozotocin-diabetic rats. Pancreatic ET levels are higher in pancreatic tissues from diabetic (D) rats compared to control (C) animals. The addition of nitric oxide synthase (NOS) inhibitors (1 mM N(G)-nitro-l-arginine methyl ester, 600 microM N(G)-monomethyl-l-arginine) in the incubating medium reduces and NO donors (SIN-1, 300 microM spermine suppress, NONOate 100 microM) increases ET levels in pancreatic slices from C and D animals. PGE(2) (10(-7) M) increases and indomethacin (10(-6) M) decreases ET pancreatic production only in D but not in C tissues when added into the incubating bath. When tissues are incubated in the presence of endothelin 1 (ET-1) (10(-7) M), NOS activity is higher in C pancreas, while the ET-receptor antagonist bosentan (B) decreases NOS levels in D but not in C tissues. When pancreatic arachidonic acid (AA) conversion to prostaglandins was explored, ET-1 increased PGF(2alpha), PGE(2), and TXB(2) levels in C but not in D tissues. B abolishes TXB(2) increment due to the diabetic state, but failed in modulating AA conversion to 6-keto PGF(1alpha), PGF2(alpha) and PGE(2) in D pancreas. Our results show an alteration in AA metabolism, ET production, and NO increment associated with pancreatic damage due to streptozotocin.

Topics: Animals; Arachidonic Acid; Diabetes Mellitus, Experimental; Dinoprost; Dinoprostone; Endothelin-1; Endothelins; Male; Molsidomine; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitrogen Oxides; omega-N-Methylarginine; Pancreas; Rats; Rats, Wistar; Spermine; Streptozocin; Thromboxane B2

Elevated IgE levels are commonly observed during the inflammatory responses in allergy and a variety of infections. This Ig activates the release of multiple mediators from monocytes/macrophages. In the present work, we attempted to clarify the IgE-dependent events involved in the activation of monocyte functions. IgE-anti-IgE immune complexes induce the production of tumor necrosis factor-alpha, oxygen radicals, IL-6 and thromboxane B2 from normal human purified monocytes. Expression and cross-linkage of Fc epsilon RII/CD23 were essential for these IgE-mediated effects. Cytokine production following CD23 ligation depended on nitric oxide transduction pathway, as it was inhibited by NG-monomethyl-L-arginine, a competitive inhibitor of the conversion of L-arginine to L-citroline by nitric oxide synthase. Furthermore, addition of the nitric oxide chemical donator, Sin-1, enhanced IgE-induced monokine release. CD23-ligation also induced the production of nitrites by these cells. This work linked CD23 to the L-arginine-dependent transduction pathway and shows their involvement in IgE-mediated stimulation of human monocytes.

Topics: Arginine; Cells, Cultured; Cytokines; Humans; Immunoglobulin E; Molsidomine; Monocytes; Nitric Oxide; omega-N-Methylarginine; Receptors, IgE; Signal Transduction; Superoxides; Thromboxane B2

The modulating effects of exogenous and endogenous nitric oxide (NO) on the cardiac anaphylactic reaction and eicosanoid release were investigated in isolated perfused sensitized guinea-pig hearts using 3-morpholinosydnonimine (SIN-1), the active metabolite of molsidomine, as NO-donor and NG-nitro-L-arginine (NNA) as an inhibitor of NO biosynthesis. Infusion of SIN-1 (final concentrations in the perfusates 0.3 or 1.0 mmol/l) elevated coronary flow under basal conditions as well as during cardiac anaphylaxis, while NNA (0.1 mmol/l) decreased basal coronary flow and aggravated the anaphylactic coronary constriction. Both drugs did not modify the characteristic biphasic profile of the coronary constriction after antigen challenge with an initial more severe phase followed by a less pronounced long-lasting flow reduction. Neither SIN-1 nor NNA affected spontaneous heart rate. However, while NNA tended to prolong the duration of antigen-induced arrhythmias, SIN-1 (1 mmol/l) had an inhibitory effect. This protection might be related to the increased coronary flow in the presence of SIN-1. SIN-1 inhibited anaphylactic release of cysteinyl-leukotrienes (LT) and 6-keto-prostaglandin (PG) F1 alpha, but did not influence thromboxane (TX) B2 release. On the other hand, NNA (0.1 mmol/l) inhibited anaphylactic release of TXB2, but had only marginal effects on the release of cysteinyl-LT and 6-keto-PGF1 alpha. The results suggest that exogenous and endogenous NO functionally antagonize the effects of vasoconstrictor mediators released after antigen challenge. Additional effects of high concentrations of SIN-1 and NNA on antigen-induced eicosanoid release could modulate the vascular actions of these drugs during cardiac anaphylaxis.

Topics: 6-Ketoprostaglandin F1 alpha; Anaphylaxis; Animals; Antihypertensive Agents; Arginine; Coronary Circulation; Guinea Pigs; Heart; Leukotriene B4; Male; Molsidomine; Nitroarginine; Perfusion; Thromboxane B2; Vasodilator Agents

Sin-1, an active metabolite of molsidomine which antagonizes platelet aggregation, was tested upon the oxygenation of arachidonic acid (AA) in these cells. While Sin-1 did not affect the formation of oxygenated derivatives of exogenous AA, it decreased markedly that of endogenous AA when platelets were triggered with thrombin or the calcium ionophore A23187. These results indicate that Sin-1 is an inhibitor of the liberation of AA from platelet phospholipids presumably by inhibiting phospholipase activity itself.

Topics: Antihypertensive Agents; Arachidonic Acid; Arachidonic Acids; Blood Platelets; Humans; Molsidomine; Oxadiazoles; Phospholipids; Sydnones; Thromboxane B2