Bode-Böger S M, Böger R H, Galland A, Frölich J C
Institute of Clinical Pharmacology, Medical School, Hannover, Germany.
Naunyn Schmiedebergs Arch Pharmacol. 1998 Feb;357(2):143-50. doi: 10.1007/pl00005148.
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+.
我们比较了内源性一氧化氮（NO）的前体L-精氨酸（L-ARG）在体内和体外对血小板聚集及血栓素A2形成的影响。富含人血小板的血浆（PRP）用柠檬酸盐（可降低细胞外Ca2+）或重组水蛭素（不影响细胞外Ca2+）进行抗凝。两组各10名健康男性志愿者接受静脉输注L-ARG（30 g或6 g，持续30分钟）或安慰剂。在输注前及输注结束时立即采血，用于检测ADP或胶原诱导的聚集。输注L-ARG可使柠檬酸盐抗凝的PRP中ADP诱导的聚集受到抑制，抑制率为37.5±6.3%（P<0.05）。在水蛭素抗凝的PRP中，聚集受到抑制，抑制率为33.6±16.0%（P<0.05）。输注L-ARG还可抑制血小板TXB2的形成，并轻微但不显著降低2,3-二去甲-TXB2的尿排泄率；在输注L-精氨酸期间，PRP中的cGMP浓度显著升高。在体外，用L-ARG（10 microM - 2.5 mM）预孵育可抑制水蛭素抗凝而非柠檬酸盐抗凝的PRP中的血小板聚集。这种作用对L-精氨酸具有立体特异性，因为D-精氨酸无此作用。如PRP中cGMP水平升高所示，其作用依赖于一氧化氮合酶活性。此外，一氧化氮合酶抑制剂L-NMMA和可溶性鸟苷酸环化酶抑制剂ODQ均可拮抗L-ARG的作用。血红蛋白是一种细胞外NO清除剂，可部分拮抗L-ARG的抗血小板作用。8-溴环鸟苷酸和外源性NO供体林西多明可抑制柠檬酸盐或重组水蛭素抗凝的PRP中的聚集。L-ARG在体外对血小板聚集的抑制作用与环鸟苷酸水平升高平行；L-ARG还可抑制重组水蛭素抗凝而非柠檬酸盐抗凝的PRP中的血小板TXB2形成。我们得出结论，L-精氨酸/NO途径在人血小板中作为一种依赖Ca2+的抗聚集途径存在。在体内，内皮细胞由L-ARG生成NO可能有助于L-ARG的血小板抑制作用。像林西多明这样的NO释放化合物在体外可独立于细胞外Ca2+抑制血小板聚集。
