Urapidil inhibits 5-hydroxytryptamine induced platelet aggregation and 14C-5-hydroxytryptamine uptake in platelets.

The effect of urapidil, an a1-antagonist with additional antihypertensive action via central 5HT1A agonism, was determined on platelet aggregation induced by 5HT and adrenaline. The 5HT uptake in human platelets was determined as well. Urapidil inhibited both the 5HT and adrenaline-induced human platelet aggregation and the 5HT uptake by platelets in vitro. The 5HT-induced aggregation was inhibited with a K1 value of 8.8 microM, the adrenaline-induced aggregation with a K1 value of 21.6 microM, and the 5HT uptake non-competitively with a K11 = 11.5 microM and a K12 = 13 microM.