The intrapancreatic endocrine regulation of hormone secretion by the chicken pancreas was studied. Fasted adult male chickens were prepared surgically for the collection of 'gastric' juice and blood samples from the femoral artery. Avian hormone preparations of insulin, glucagon and pancreatic polypeptide (APP) were injected at doses of 50 μg hormone/ kg body wt. Immunoassays of insulin, glucagon and APP were carried out on plasma, as were analyses for glucose, uric acid and free fatty acids (FFA). Gastric juice was analysed for volume flow and total protein, free acid and pepsin concentrations.
Injection of insulin decreased all gastric parameters markedly (in contrast to its effect in mammals) and also increased the concentrations of FFA, glucagon (a bimodal response) and uric acid. The increases in levels of FFA, glucagon and uric acid occurred as early as 2·5 min after injection and considerably before significant hypoglycaemia was induced (15–30 min). Injection of glucagon caused a modest decrease in the volume of gastric secretion, but had little other effect except for a small increase in the amount of pepsin released. At 2·5 min, glucagon gave rise to a significant increase in the levels of insulin and FFA in the plasma, and after 15 min the levels of glucose and uric acid had also increased. A progressive decrease in the concentration of APP in the plasma was observed, which was greatest after 15 min and was 28% below control values. In all respects, APP was a powerful avian gastric secretogogue, but had no effect on the concentrations of plasma glucose and insulin. Whereas APP decreased the concentration of FFA in the plasma immediately, the peptide increased both the total and pancreatic levels of immunoreactive glucagon by 50% within 2·5 min, and this increase was even greater at 15 min.
Collectively, the results obtained indicate, on a temporal basis, that intrapancreatic regulation of endocrine secretion occurs in Aves and that the release phenomena produce an immediate response. Subsequent or secondary hormone release may occur in response to peripheral metabolic events, especially those requiring homeostatic corrective measures.
Intrapancreatic Ganglia and Neural Regulation of Pancreatic Endocrine Secretion
