Exogenous serotonin and histamine-stimulated gastric acid and pepsin secretion in dogs

The effects of serotonin on histamine-stimulated gastric acid and pepsin secretion were evaluated in conscious dogs with a gastric fistula. Histamine stimulated the acid secretion dose-dependently, whereas pepsin secretion was decreased by the high doses of histamine. The acid secretion was inhibited slightly by serotonin, with a maximum of 42% with a dose of 10 micrograms/kg/min. The pepsin secretion was only decreased non-significantly by serotonin, 10-15 micrograms/kg/min. The acid inhibition was counteracted by beta-adrenergic antagonists (propranolol, atenolol) and methysergide (serotonergic antagonist). The dose-response analysis showed inhibition of a competitive type. In conclusion, serotonin inhibits histamine-stimulated gastric acid secretion via serotonergic receptors and beta-adrenoceptors, whereas pepsin secretion is unaffected.