EFFECTS OF 5-HYDROXYTRYPTAMINE AND MORPHINE ON THE STOMACH MOTILITY IN SITU

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Abstract
5-Hydroxytryptamine [5-HT] and morphine inhibited stomach motility of unanesthetized cats but did produce a slight contraction of the stomach of anesthetized cats. In unanesthetized rabbits, 5-HT caused a contraction, followed by an inhibition of motility, and morphine depressed motility. The 5-HT-induced contraction is a direct action on smooth muscle and the inhibition of spontaneous movement due to 5-HT may be, in part, mediated through catecholamine-release and in part, result from paralysis of the receptors for 5-HT in the cholinergic nerves in the stomach. In anesthetized rabbits, 5-HT produced contraction and morphine had no effect. In unanesthetized guinea pigs, 5-HT caused a contraction and morphine abolished spontaneous movement of the stomach. In anesthetized guinea-pigs, 5-HT caused contraction and morphine produced no effect. The 5-HT induced contraction of the guinea pig stomach is indirect. The differences in the modes of actions of 5-HT and morphine on gastric motility are related to differences in species and experimental conditions such as anesthesia.