Comparison of vasoactive intestinal peptide and secretin in stimulation of pancreatic secretion.

Abstract

Pancreatic volume flow and bicarbonate and protein secretion were measured in chronic pancreatic fistula cats and dogs in response to i.v. infusion of vasoactive intestinal protein [VIP] and secretin or duodenal perfusion of sodium oleate and HCl solution. VIP and secretin infused i.v. in cats produced superimposable pancreatic dose-response curves for volume flow and bicarbonate secretion, reaching almost identical observed and maximal calculated outputs with both peptides. In dogs, VIP was shown previously to be a much less effective stimulant of pancreatic secretion than secretin and the maximal observed bicarbonate output in response to VIP was only about 17% of that to secretin. VIP in cats is a secretin-like full agonist; in dogs it is a partial agonist of pancreatic bicarbonate secretion. In cats, secretin and VIP showed equal efficacy and their combination exhibited an augmentatory action on pancreatic bicarbonate secretion with additive kinetics; in dogs, VIP had a lower efficacy than secretin and inhibited competitively secretin-induced pancreatic secretion. These results might be explained by the interaction of VIP and secretin, 2 chemically related peptides, on a common receptor site of the exocrine pancreas. Caerulein, an analogue of cholecystokinin-pancreozymin [CCK-PZ], infused i.v. in cats and dogs caused a negligible pancreatic bicarbonate secretion and a potent dose-dependent protein secretion. The combination of graded doses of VIP or secretin with a background dose of caerulein resulted in significantly higher bicarbonate and protein outputs than those induced by VIP or secretin alone. Duodenal perfusion of sodium oleate soap in cats and dogs produced pancreatic dose-response curves for volume flow and bicarbonate output similar to those evoked by VIP in these species. Pancreatic protein secretion in response to luminal oleate was slightly higher than could be accounted for by the action of VIP alone. This might be attributed to the release by oleate not only of endogenous VIP but also CCK-PZ or to the vago-vagal reflexes from gut to pancreas. Oleate may release VIP from the gut. This peptide may play a physiological role in the stimulation of pancreatic secretion.