Platelet-mediated vascular contractions: inhibition of the serotonergic component by ketanserin.

In vitro stimulation of washed rat platelets (2.5 X 10(10)/1) with thrombin (0.002 U/1) as well as their activation on de-endothelialized vascular preparations, produced a strong contraction of isolated rat caudal arteries. Pharmacodissection and specific measurements of various mediators (5-hydroxytryptamine, thromboxane B2, ATP) showed the platelet-mediated contraction to be mainly mediated by 5-hydroxytryptamine, either by its direct effect or through amplification of prostaglandin-effects at the level of the vessel or the platelets. Platelet-mediated vasospastic episodes were effectively reduced by ketanserin, a selective 5-HT2 receptor antagonist.