Excitatory action of sympathomimetic amines on 5‐hydroxytryptamine receptors of gut

Abstract

1 Twenty-two sympathomimetic amines were tested for excitatory activity on isolated guinea-pig ileum, rabbit jejunum, and rat stomach. 2 Eight amines contracted all or almost all guinea-pig ileum preparations; five amines contracted half the preparations and relaxed the others. Nine amines were consistently relaxant. Structural requirements for excitatory activity were not clear. 3 Six amines contracted rat stomach and only four contracted rabbit jejunum. Only β-phenylethylamine and (—)-amphetamine contracted all three preparations. 4 The excitatory effects of the sympathomimetic amines on guinea-pig ileum seem to be due to an action on 5-hydroxytryptamine receptors. This conclusion is based on evidence that their excitatory action is antagonized by 2-bromo-Iysergic acid diethylamide, by morphine and by desensitization with 5-hydroxytryptamine, and that there is cross-protection between 5-hydroxytryptamine and the excitatory sympathomimetic amines against block by phenoxybenzamine.