Effect of Peptide YY on Cephalic, Gastric, and Intestinal Phases of Gastric Acid Secretion and on the Release of Gastrointestinal Hormones

The objective of this study was to investigate the effects of a novel gut peptide, peptide YY (PYY), on the cephalic, gastric, and intestinal phases of gastric acid secretion and to explore the mechanisms involved. The cephalic phase of gastric acid secretion, stimulated by the intravenous injection of 2-deoxyglucose (75 mg/kg), was found to be inhibited by intravenous PYY (100, 200, 400 pmol/kg - h) in a dose-related fashion. Peptide YY (200 and 400 pmol/kg - h) also resulted in a significant dosedependent inhibition of the gastric phase of acid secretion. On the other hand, PYY (400 pmol/kg - h) failed to affect the intestinal phase of gastric acid output. Serum gastrin levels were increased on infusion of 10% liver extract into stomach, but were unaffected on instillation of liver extract into duodenum. Peptide YY did not inhibit the release of gastrin in either the gastric or intestinal phase studies. Furthermore, PYY had no significant effect on either the basal release of secretin, gastric inhibitory polypeptide, pancreatic polypeptide, or neurotensin, or on the stimulated release` of pancreatic polypeptide by 2-deoxyglucose. The specific binding of gastrin to its receptors on the fundic mucosa was also unaffected by PYY. These results indicate that PYY inhibits the cephalic and gastric phases of acid secretion independently, and that its actions are not mediated by either a negative effect on gastrin release or a positive effect on the release of some of the known acid inhibitors, or by an inhibition of gastrin binding to its receptors on the fundic cells. Our present findings (in combination with our previous findings of inhibition of pentagastrin- and bethanechol-stimulated gastric acid secretion by PYY, independent of the vagal cholinergic mechanism) indicate that the action of PYY is either direct on the parietal cells or is mediated by yet another, unidentified, inhibitor.