Regional vascular effects of serotonin and ketanserin in young, healthy subjects.

The local hemodynamic effects of serotonin (5-hydroxytryptamine; 5-HT) and the selective 5-HT2 antagonist ketanserin were investigated in the forearm of 20 healthy volunteers. Single doses of 5-HT (0.1-80 ng/kg/min) and ketanserin (5-125 ng/kg/min) were administered intra-arterially. The relative alpha 1-adrenergic receptor and 5-HT2 blocking potencies of ketanserin were investigated using intra-arterial infusions of cumulative doses of methoxamine (0.1, 0.3, and 0.5 microgram/kg/min), tyramine (0.25, 0.50, and 1.25 microgram/kg/min), and 5-HT (10, 30, and 80 ng/kg/min) together with a low dose (5 ng/kg/min) and a high dose (50 ng/kg/min) of ketanserin. Forearm blood flow was measured by venous occlusion plethysmography. Heart rate and intra-arterial blood pressure were recorded semicontinuously. Intra-arterial infusion of 5-HT induced an initial transient vasodilatation, followed by a steady vasodilatation for the low doses of 5-HT (0.1-10 ng/kg/min; p less than 0.05). A steady vasoconstriction was only obtained at the highest dose of 5-HT. Ketanserin induced a dose-dependent increase in forearm blood flow from 15 ng/kg/min (p less than 0.05) onward. The vasodilatation induced by 5-HT (1 ng/kg/min) was significantly enhanced by ketanserin (125 ng/kg/min; p less than 0.05), whereas the vasoconstriction elicited by 5-HT (80 ng/kg/min) was reversed by ketanserin (50 ng/kg/min; p less than 0.05), thus confirming that 5-HT2 receptors were stimulated by 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)