Pancreatic volume flow as well as
bicarbonate and
protein secretion have been measured in chronic
pancreatic fistula cats and dogs in response to I.V. infusion of VIP and
secretin or duodenal perfusion of
sodium oleate and HCl
solution. 2. 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 (Konturek, Thor, Dembinski & Król, 1975). It is condluded that VIP in cats is a
secretin-like full agonist, whereas in dogs it is a partial agonist of pancreatic
bicarbonate secretion. 3. In cats,
secretin and VIP showed equal efficacy and their combination exhibited an augmentatory action on pancreatic
bicarbonate secretion with additive kinetics, whereas in dogs, VIP was found to have a lower efficacy than
secretin and to inhibit competitively
secretin-induced pancreatic secretion. These results might be explained by the interaction of VIP and
secretin, two chemically related
peptides, on a common receptor site of the exocrine pancreas. 4.
Caerulein, an analogue of 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. 5. 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. The results of our combined study on cats and dogs suggest the possibility that
oleate releases VIP from the gut and that this
peptide may play a physiological role in the stimulation of pancreatic secretion.