5-Hydroxytryptamine M-receptor antagonism in the hypothalamus facilitates gastric emptying in the guinea-pig.

The injection of 5-hydroxytryptamine (5-HT) and 2-methyl-5-HT into the perifornical area of the hypothalamus of the guinea-pig reduced the emptying of barium sulphate spheroids from the stomach. In contrast, the injection of the 5-HT M-receptor antagonist ICS 205-930 into the same area of the hypothalamus enhanced gastric emptying and attenuated the inhibitory effect of 5-HT. Similar injections of methysergide and ritanserin were without effect. It is concluded that an endogenous hypothalamic 5-HT system may inhibit gastric emptying through a 5-HT M-receptor mechanism which may afford a site of action for 5-HT agonist and antagonist drugs to modify gastric emptying.