Regulation of gastric acid secretion by secretin and serotonin

We have tested the interaction between serotonin and secretin in pentagastrin-induced gastric acid secretion in six dogs prepared with Thomas gastric and duodenal cannulas. We further examined the effect of methysergide, a serotonin antagonist, on gastric acid secretion. The intravenous administration of serotonin or secretin alone significantly inhibited pentagastrin-induced gastric acid secretion. The combined administration of serotonin and secretin inhibited gastric acid secretion to a greater magnitude than either secretagogue alone. The administration of methysergide diminished basal concentrations of secretin on gastric acid secretion. Methysergide also enhanced the stimulatory activity of pentagastrin-induced gastric acid secretion. The inhibitory action of intraduodenal acidification of pentagastrin-induced gastric acid secretion was reversed by methysergide.