PERSISTENCE OF IMMUNOREACTIVE INSULIN, GLUCAGON AND PANCREATIC POLYPEPTIDE IN THE PLASMA OF DEPANCREATIZED CHICKENS

Abstract

The present study evaluates the possibility that an extra-pancreatic source of insulin exists in chickens. The effect of pancreatectomy on plasma levels of immunoreactive insulin (IRI), glucagon (IRG) and pancreatic polypeptide (IRAPP) was examined. Plasma levels of IRI, IRG and IRAPP were measured both in the basal state and after an i.v. challenge with known secretogogues at several times after pancreatectomy. The nature of the avian plasma immunoreactivity was further characterized by gel filtration. Results indicated that plasma IRI and IRG persisted for 5 h, 24 h and 5 days after pancreatectomy. Furthermore, plasma levels of IRI and IRG remained responsive to the stimulus of i.v. arginine. The Sephadex G-50 elution profiles for IRI and IRG were similar for plasma obtained from both depancreatized and intact chickens. Postmortem tissue analyses indicated that the persistence of IRI and IRG in the depancreatized animals was not due to the presence of pancreatic remnants. Plasma IRAPP decreased to undetectable levels 5 h after pancreatectomy. Although plasma IRAPP was measurable 1 and 5 days after pancreatectomy, these levels were not responsive to i.v. pentagastrin. Furthermore, gel filtration experiments indicated that the only form of IRAPP remaining after pancreatectomy had an apparent mol. wt of greater than 100 000. Such a compound was not secreted by the pancreas in vitro. Evidence presented herein indicates that pancreatic polypeptide is the only pancreatic hormone to be eliminated from the circulation after pancreatectomy in chickens. It is suggested that the depancreatized chicken might be useful as a model of a 'selective' pancreatic polypeptide deficiency.