The effect of pituitary adenylate cyclase activating polypeptide (PACAP) on exocrine pancreatic secretion in dogs

The effect of new hypothalamic peptides, PACAP38 and PACAP27, on exocrine pancreatic secretion was studied in five conscious dogs each with a chronic gastric fistula and a Thomas duodenal fistula. The intravenous injections of PACAP38 and PACAP27 (2.5-100 pmol/kg) induced dose-related increases in pancreatic fluid, bicarbonate, and protein secretion. The potency of PACAP27 was equal to that of VIP but was only 1/100 that of secretin; PACAP38 was less active (less than 1/10) than PACAP27. PACAP38 and PACAP27, in contrast to secretin and VIP, stimulated protein secretion; the potency of the former was about 1/10 that of the latter. The peak response to PACAP27 was about 44% of the maximal response to CCK8. Pancreatic protein secretion, but not fluid and bicarbonate secretion, in response to PACAP38 and PACAP27 was significantly (p less than 0.05) reduced by atropine. It is concluded that PACAP has a VIP-like action on pancreatic fluid and bicarbonate secretion in conscious dogs, but differs from VIP in stimulating protein secretion via a cholinergic mechanism.