Ketanserin causes surmountable antagonism of 5-hydroxytryptamine-induced contractions of large coronary arteries of dog.

Large coronary arteries of the dog were contracted with 5-hydroxytryptamine (5-HT). The 5-HT2-receptor antagonist ketanserin antagonized the 5-HT-induced effects. Unlike Brazenor and Angus (Europ J Pharmacol 81:569-576, 1982) who reported insurmountable antagonism of the effects of 5-HT in dog coronaries, we found that the antagonism by ketanserin can be surmounted, provided the concentrations of 5-HT are high enough. Ketanserin also unmasked a saturable component of the 5-HT-induced contractions. Although ketanserin (0.1-1 mumol/l) depressed the maximal force of the saturable component, it did not change its EC50 (-log mol/l 8.0). We conclude that large coronary arteries of dog are contracted by 5-HT mainly through 5-HT2-receptors and to a smaller extent through receptors different from 5-HT2.