title: Antagonism by ketanserin of 5-HT-induced vasoconstriction unmasks a 5-HT-induced vasodilation.
abstract: The effect of ketanserin on the action of 5-hydroxytryptamine (5-HT) and noradrenaline has been studied using the rat isolated perfused mesentery preparation. Both 5-HT and noradrenaline produced constriction in the mesenteric vessels. The responses to 5-HT and noradrenaline were greater in tissues from hypertensive animals. Responses to 5-HT were abolished by 1 nM ketanserin. Ketanserin was found to be a competitive antagonist of the noradrenaline-induced constrictions (pA2 = 7.5). In partially constricted tissues, 5-HT induced vasoconstriction and vasodilation. In the presence of ketanserin the vasoconstriction was reduced and the 5-HT-induced vasodilation was potentiated. The amount of potentiation of the 5-HT-induced vasodilation by ketanserin was similar in tissues from normotensive and hypertensive rats. It is suggested that the 5-HT-induced vasoconstriction is mediated by activation of 5-HT2 receptors. In the presence of ketanserin, the 5-HT2 receptor mediated vasoconstriction is antagonized, unmasking a 5-HT-induced vasodilation.
mesh_terms: D000578:Amidines / Q000494:pharmacology; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D006973:Hypertension / Q000503:physiopathology; D066298:In Vitro Techniques; D007650:Ketanserin; D008297:Male; D009638:Norepinephrine / Q000037:antagonists & inhibitors; D010880:Piperidines / Q000494:pharmacology*; D051381:Rats; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology*; D014661:Vasoconstriction / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D000578:Amidines; D000959:Antihypertensive Agents; D010880:Piperidines; D012702:Serotonin Antagonists; D012701:Serotonin; C029751:BW 501C; D007650:Ketanserin; D009638:Norepinephrine