Possible central antisecretory action of exogenous serotonin in rats

The effect of exogenous serotonin (10 mg/kg i. p.) in rats pretreated and unpretreated with 6-hydroxydopamine, propranolol or with alpha-methyltyrosine on intragastric pH was studied. It was observed that after serotonin administration, the intragastric pH increased by approximately five units. The chemical sympathectomy by administration of 6-hydroxydopamine did not alter significantly either basal intragastric pH or the serotonin-induced increase of intragastric pH. The administration of propranolol did not alter significantly the basal intragastric pH, whilst the pretreatment with propranolol abolished the antisecretory effect of serotonin. Repeated dosages with alpha-methyl tyrosine did not alter the basal intragastric pH, but inhibited the effect of serotonin or intragastric pH. These results seem to indicate that the antisecretory effect of exogenous serotonin on gastric acid output, is caused by the inhibition of the vegetative brain centres responsible for the secretory activity of the parietal cells. Furthermore, it is suggested that the antisecretory effect of serotonin is mediated by a release of noradrenaline from the brain adrenergic neurones.