Effect of pancreatic polypeptide and its C-terminal hexapeptide on meal and secretin induced pancreatic secretion in dogs.

1. Gastric acid and pancreatic bicarbonate and protein secretion as well as immunoreactive serum gastrin and pancreatic polypeptide concentrations in response to a meal and secretin have been measured before and after infusion of bovine pancreatic polypeptide or its C-terminal hexapeptide. 2. Liver extract meal kept in the stomach at pH 5.5 (by intragastric titration) produced a marked increase in gastric acid and pancreatic protein secretion accompanied by a rise in serum gastrin and pancreatic polypeptide levels. Exogenous bovine pancreatic polypeptide caused little change in gastric secretion and serum gastrin but resulted in a profound suppression of pancreatic secretion. 3. Ordinary feeding a liver meal produced a marked increase in pancreatic bicarbonate and protein secretion that was dose-dependently inhibited by bovine pancreatic polypeptide or its C-terminal hexapeptide, the degree of inhibition being closely correlated with the increments in plasma pancreatic polypeptide. 4. Bovine pancreatic polypeptide and its C-terminal hexapeptide also inhibited secretin and caerulein-induced pancreatic secretion in a dose-dependent manner. 5. This study shows that bovine pancreatic polypeptide inhibits pancreatic secretion at least in part by acting directly on the exocrine pancreas and that its biological activity resides in its C-terminal hexapeptide fragment.