EFFECT OF PACAP ON GASTRIC-ACID SECRETION IN RATS

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a new VI P-like blain-gut peptide. Its effects on the motility and secretory fu nctions of the gastrointestinal system have been shown in previous stu dies. In this study we investigated the effect of intravenous PACAP on gastric acid secretion in conscious pylorus-ligated rats and in gastr ic fistula rats. PACAP showed significant inhibitory effects on pentag astrin- and histamine-stimulated gastric acid secretion, but no effect on basal or carbachol-stimulated secretion in pylorus-ligated rats. I t did show dose-related inhibitory effects both on basal gastric acid secretion and on secretion stimulated by pentagastrin, histamine, or c arbachol in gastric fistula rats. PACAP did not alter serum gastrin le vels. Inhibition of prostaglandin synthesis with indomethacin and immu noneutralization of somatostatin with anti-somatostatin serum did not prevent the inhibitory effect of PACAP on gastric acid secretion in py lorus-ligated rats. We conclude that PACAP most likely has a direct ef fect on parietal cells and that this effect may be mediated, at least partially, by inhibition of the action of histamine on parietal cells.