Potentiation of endoperoxide analog-induced platelet aggregation by heparin

The mechanism of heparin-induced platelet aggregation potentiation is much debated. We examined the effects of heparin on platelet aggregation induced by cyclic endoperoxide analog u46, 619. Heparin enhanced platelet aggregation in a dose-related fashion. Potentiation of platelet aggregation was also found to be related to the incubation time of heparin and platelet rich plasma. Porcine intestinal heparin and bovine lung heparin exhibited similar patterns. To test the hypothesis of increased platelet thromboxane A2 production under the influence of heparin, we measured U46,619-induced thromboxane A2 generation. Heparin was found not to affect platelet thromboxane A2 generation over a wide range of concentrations. The platelet aggregation potentiating actions of heparin are thus unrelated to thromboxane A2 pathway.