Secretin has been recognized as an important enterogastrone. In order to investigate the mechanism of secretin-induced inhibition of gastric acid secretion, the effects of both anti-somatostatin antibody and indomethacin on acid secretion were examined in conscious rats with gastric cannulas. 2. Secretin given intravenously at 5.6 pmol kg-1 h-1 inhibited profoundly the acid secretion stimulated by pentagastrin at 0.3 microgram kg-1 h-1. 3. When a rabbit antisomatostatin serum was given intravenously, it not only abolished the secretin-induced inhibition on the pentagastrin-stimulated acid secretion, but also augmented both basal and pentagastrin-stimulated acid secretion. 4. Indomethacin also significantly augmented basal acid secretion, starting 45 min after the drug delivery began. It reversed the secretin-induced inhibition but it did not augment the pentagastrin-stimulated acid secretion. 5. Neither antisomatostatin serum influenced prostaglandin E2-induced inhibition of the pentagastrin-stimulated acid secretion, nor did indomethacin affect the inhibition by somatostatin, suggesting strongly that the inhibition by somatostatin is not mediated by endogenous prostaglandins, nor is that by prostaglandins E2 mediated by endogenous somatostatin. 6. It is concluded that the inhibitory action of secretin on pentagastrin-stimulated gastric acid secretion is mediated by both somatostatin and prostaglandins in conscious rats. The two inhibitors do not seem to interact endogenously for the inhibition of acid secretion. While endogenous somatostatin exerts a tonic inhibitory effect on both basal and pentagastrin-simulated acid secretion, prostaglandins augment basal acid secretion only.
