Potentiation of the inhibitory effect of a thromboxane A2 antagonist (L-640,035) on arterial thrombosis formation in rabbit by the angiotensin converting enzyme inhibitor enalapril

The angiotensin converting enzyme inhibitor enalapril (0.5 mg/kg i.v.) potentiated significantly the inhibitor effect of the thromboxane A₂ antagonist L-640,035 (1 mg/kg i.v.) on electrically induced platelet accumulation in the rabbit in vivo. Enalapril had no effect upon platelet accumulation when given alone. The hypotensive effects of enalapril did not account for the potentiation because a combination of hexamethonium (5 mg/kg i.v.) and hydralazine (1 mg/kg i.v.), which decreased blood pressure similarly to enalapril, did not augment the effect of L-640,035. Determination by radioimmunoassay of plasma levels of immunoreactive 6-keto-PGF_1α, suggested that increases in PGI₂ levels after combined administration of enalapril and L-640,035 could explain the observed potentiation.