Comparison of the contraction produced by various tryptamine analogues on human basilar arterial and rat aortic strips in vitro.

The effect of various closely related analogues of 5-hydroxytryptamine were studied on the human basilar arterial and rat aortic strips in vitro. All analogues (except 5-methoxytryptamine) contracted both preparations producing maximal responses equivalent to that obtained with 5-hydroxytryptamine. Maximum responses to 5-methoxytryptamine were equivalent to and only 60% of the maximum obtained with 5-hydroxytryptamine on human basilar artery and rat aorta, respectively. The order of potency of the analogues on the human basilar artery was different from that obtained on the rat aorta. 5-methyltryptamine, N-methyltryptamine and tryptamine were equipotent on both tissues, whereas 5-hydroxytryptamine and 5-methoxytryptamine were 229 and 296 times more potent, respectively, on the human basilar artery compared to the rat aorta. Both tissues appear to be deficient in monoamine oxidase, since nialamide or iproniazid did not potentiate responses to tryptamine. It is concluded that the receptor type mediating contraction of the human basilar artery to 5-hydroxytryptamine is different from the classical smooth muscle D-receptor.