Pressor effect of indolethylamines

6-Hydroxytryptamine, 7-hydroxytryptamine and 5,7-dihydroxytryptamine increase blood pressure when given intravenously to pithed rats and effect not due to stimulation of 5-hydroxytryptamine receptors. 6-Hydroxytryptamine and 7-hydroxytryptamine interact with α-adrenoceptors of the vascular bed. An effect of 5,7-dihydroxytryptamine on α-adrenoceptors was not established.