Effects of vinblastine on malondialdehyde formation, serotonin release and aggregation in human platelets

Effects of the microtubular agent vinblastine on human platelet malondialdehyde formation, 14C]serotonin release and aggregation were studied in suspensions of 14C]serotonin-labelled platelets. Vinblastine caused dose-dependent inhibition of malondialdehyde formation and aggregation in platelet suspensions stimulated with thrombin, ADP or palmitaldehyde acetal phosphatidic acid (PGAP). Malondialdehyde formation, aggregation and 14C]serotonin release caused by threshold doses of thrombin were reduced but not abolished by 100 muM vinblastine; 30-100 muM vinblastine abolished ADP- and PGAP-induced malondialdehyde formation and 14C]serotonin released and transformed ADP- and PGAP-induced irreversible aggregation to a diminished reversible response. Arachidonate conversion to malondialdehyde catalysed by human platelet microsomes was inhibited by vinblastine and the cyclooxygenase inhibitors indomethacin and aspirin, but not by salicylate. Vinblastine inhibited the microsome-catalysed formation of malondialdehyde from prostaglandin H2. It is concluded that vinblastine inhibits the thromboxane pathway of arachidonate metabolism in stimulated platelets, consequently inhibiting release and aggregation, and that this effect of vinblastine may be, at least in part, independent of its antimicrotubular actions.