Comparison of the actions of serotoninergic agents on human saphenous veins and platelets.

Changes in tension of helical strips from human saphenous veins and reversible aggregation of human platelets were recorded in vitro. Comparison of the activities of 12 serotonin receptor agonists revealed that only 4 of the investigated tryptamine derivatives acted as full agonists on both tissues. 5-Carboxamidotryptamine, a drug with selective affinity for both 5-HT1A and 5-HT1B binding sites, though the most potent agonist on veins, failed to produce platelet aggregation but acted as a weak antagonist of the 5-HT-induced reversible aggregation. The tetralin derivative 8-OH-DPAT, a drug with selective affinity for 5-HT1A binding sites, was a weak partial agonist on veins and completely devoid of any activity on the platelets. The antagonism of 5-HT by spiperone was monophasic on platelets but biphasic on veins. These data are in line with the contention that the 5-HT-induced reversible aggregation of human platelets is initiated by 5-HT2-like recognition sites while the evidence suggests that the contractile response of human saphenous vein to 5-HT reflects activation of both 5-HT2- and 5-HT1-like recognition sites.