Inhibition of thromboxane A2 biosynthesis in human platelets by burimamide

1 Burimamide selectively inhibited the formation of thromboxane A2 from prostaglandin endoperoxides by human platelet microsomes in a dose-dependent manner (IC50 = 2.5 x 10(-5) M). Burimamide was found to be equipotent to imidazole as a thromboxane synthetase inhibitor. 2 Metiamide, cimetidine and a series of compounds either bearing a structural or pharmacological relationship to histamine caused little or no inhibition of thromboxane A2 biosynthesis by human platelet microsomes. 3 Burimamide (5 x 10(-4) to 2.3 x 10(-3) M) did not inhibit either the cyclo-oxygenase or the prostacyclin synthetase of sheep seminal vesicles or the prostacyclin synthetase of dog aortic microsomes. 4 Burimamide (2.5 x 10(-5) to 1.2 x 10(-4) M) inhibited sodium arachidonate-induced human platelet aggregation; the degree of inhibition was dependent upon the concentration of arachidonic acid used to aggregate the platelets.