Continuous inhibition of platelet S2-serotonergic receptors during chronic administration of ketanserin in humans.

Platelet aggregation induced by serotonin in plasma obtained from 9 volunteers was inhibited at 90 min and 15 h after the oral administration of ketanserin, either acutely or after one week of chronic administration. At 7 days after the last dose, a transient overreaction to serotonin occurred. Platelet reactions to epinephrine, collagen and adenosine diphosphate were not affected by ketanserin. The present results demonstrate a continuous inhibition of S2-serotonergic receptors in platelets during both acute and chronic treatment with ketanserin in humans.