PHENOXYBENZAMINE ANTAGONISM OF TRYPTAMINES, THEIR INDENE ISOSTERES AND 5-HYDROXYTRYPTAMINE IN THE RAT STOMACH FUNDUS PREPARATION

¹ Department of Pharmacology, State University of New York, Buffalo, New York

Examination of the effects of the competitive irreversible antagonist phenoxybenzamine on the responses to the tryptamines, their indenealkylamine isosteres and 5-hydroxytryptamine (5-HT) indicates that more than one contractile tryptamine receptor is present in the rat stomach fundus. Although the responses to tryptamines and their isosteres are blocked by phenoxybenzamine, the degree of block is significantly less than for 5-HT. These drugs, therefore, can be assumed to act on a second, phenoxybenzamine-resistant, receptor, which has been designated the PRT receptor. It was found that tryptamine, N, N-diethyltryptamine and the indenealkylamines isosteric with them, as well as 5-HT, are able to protect the responses to 5-UT against block by phenoxybenzamine. These receptor-protection experiments establish that the tryptamines and their isosteres occupy the 5-HT receptor as well as the PRT receptor.