Characterization of 5-hydroxytryptamine receptors mediating circular smooth muscle contraction in the human umbilical artery

The study was performed to characterize pharmacologically the contractile 5 -hydroxytryptamine (5-HT) receptors in the circular smooth muscle of the is olated human umbilical artery. Effects of agonists and antagonists for diff erent 5-HT receptor subtypes were studied in intact endothelium vessel segm ents. All agonists induced concentration-dependent circular smooth muscle c ontractions. The potency was in declining order 5-HT > alpha-methyl-5-HT > sumatriptan greater than or equal to 2-methyl-5-HT. The effects of 5-HT and alpha-methyl-5-HT were antagonized by ketanserin, as well as methiothepin, The contractile effect of sumatriptan was antagonized by methiothepin but not by ketanserin. The 5-HT3 receptor antagonist, MDL 72222, did not affect the contraction by any of the agonists, including 2-methyl-5-HT. It is con cluded that the 5-HT-induced contraction in the circular smooth muscle of t he human umbilical artery seems to be mediated by a mixed population of 5-H T1-like receptors and 5-HT2 receptors.