Immunoneutralization of circulating pancreatic polypeptide and pancreatic secretion.

To determine the role of endogenous pancreatic polypeptide (PP) as a physiological inhibitor of pancreatic secretion, normal rabbit serum (control) or rabbit PP-antiserum was administered intravenously to dogs with chronic esophageal, gastric, and pancreatic fistulas. In all dogs tested, sham-feeding and ordinary feed with a meat meal resulted in a marked rise in the plasma level of immunoreactive PP that coincided with an increase in the exocrine pancreatic secretion of HCO3- and protein. After intravenous administration of PP antiserum, endogenous plasma PP was almost completely bound by infused antibodies to PP, whereas no such binding was detected after infusion of normal rabbit serum. In contrast, plasma gastrin remained unchanged both under basal and stimulated conditions. Immunoneutralization of PP, released endogenously, failed significantly to affect gastric acid and pancreatic protein responses to sham-feeding and the pancreatic HCO3- and protein responses to feeding a meat meal in chronic pancreatic fistula dogs. However, the PP antiserum abolished, in part, the inhibitory effect of exogenous PP on pancreatic secretion stimulated by exogenous hormones. We conclude that endogenous PP is not a physiological inhibitor of exocrine pancreatic secretion, as has been suggested previously.