title: Differential inhibition of human platelet aggregation and thromboxane A2 formation by L-arginine in vivo and in vitro.
abstract: 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+.
authors.affiliation: Institute of Clinical Pharmacology, Medical School, Hannover, Germany.
authors.forename: S M
authors.initials: SM
authors.lastname: Bode-Böger
authors.forename: R H
authors.initials: RH
authors.lastname: Böger
authors.forename: A
authors.initials: A
authors.lastname: Galland
authors.forename: J C
authors.initials: JC
authors.lastname: Frölich
mesh_terms: D000328:Adult; D000991:Antithrombins / Q000494:pharmacology; D001120:Arginine / Q000008:administration & dosage / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007262:Infusions, Intravenous; D008297:Male; D008981:Molsidomine / Q000031:analogs & derivatives / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D013928:Thromboxane A2 / Q000096:biosynthesis*; D013929:Thromboxane B2 / Q000031:analogs & derivatives / Q000652:urine; D013931:Thromboxanes / Q000031:analogs & derivatives*
chemical_list: C089757:2,3-dinorthromboxane B1; D000991:Antithrombins; D004791:Enzyme Inhibitors; D010975:Platelet Aggregation Inhibitors; D013931:Thromboxanes; C016276:8-bromocyclic GMP; D013929:Thromboxane B2; D013928:Thromboxane A2; C002385:linsidomine; D001120:Arginine; D008981:Molsidomine; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP