The inhibitory action of 5-hydroxytryptamine on gastric secretory function in rats

The inhibitory action of 5-hydroxytryptamine (5-HT) on gastric function was studied in vagotomized rats. 5-HT (0.6, 1 or 5 mgkg-1, s.c.) dose-dependently reduced gastric acid secretion evoked by histamine, pentagastrin or methacholine. Pepsin secretion induced by pentagastrin or methacholine was also depressed by 5-HT. Basal secretion of both acid and pepsin was not significantly affected by any of the three 5-HT doses. Indomethacin pretreatment, which significantly decreased gastric mucosal prostaglandin E2 content, did not modify the inhibitory effects of 5-HT on histamine-induced acid secretion, nor did phentolamine or propranolol. This study suggests that 5-HT inhibits gastric secretory function through mechanisms other than by sympathetic influence or increased prostaglandin synthesis. The inhibitory action appears not to be vagus-dependent. Other mechanisms of action are discussed.