Shortening of the bleeding time in thrombocytopenic rabbits after exposure of jugular vein to high aspirin concentration.

Aspirin, in doses which inhibit platelet thromboxane A2 production, prolongs the bleeding time but this effect on the bleeding time is lost when doses of aspirin which also inhibit vessel wall prostaglandin I2 (PGI2) production are used. PGI2 is both a potent inhibitor of platelet aggregation and a powerful vasodilator. We have investigated the contribution of the vascular effect of PGI2 on hemostasis by studying the effect of high concentrations of aspirin on the jugular vein bleeding time in severely thrombocytopenic rabbits and on the loss of non-platelet-containing fluid from standard puncture wounds in aspirin-treated veins perfused under constant pressure. After aspirin treatment, the bleeding time was significantly shortened in both normal and thrombocytopenic rabbits. This effect was associated with a decreased production of PGI2-like material by the vessel wall and a reduction in the volume of fluid lost from the standard puncture wound in the jugular vein. The effect of aspirin on the bleeding time and on PGI2 production was relatively short-lived and the bleeding time returned to normal within 2-3 hours. These observations indicate that PGI2 can influence hemostasis by mechanisms independent of platelet aggregation.