Alpha- and Beta-Adrenergic Control of Pancreatic Polypeptide and Insulin Secretion in Adult Chickens 1

Abstract

Abstract

Adult, unanesthetized but restrained chickens were cannulated via appropriate femoral arteries and veins to assess alpha, beta-adrenergic regulation of pancreatic secretion of insulin (IRI) and pancreatic polypeptide (APP) during glucose infusions alone or with simultaneous infusion of either phentolamine (alpha blocker) or propranolol (beta blocker). Plasma samples were obtained over 30 or 60 min and assayed for glucose, insulin, and pancreatic polypeptide. Glucose (0.88 g/kg, bolus or infusion—30 min) provoked an immediate rise in IRI even when plasma glucose levels peaked at 350 mg/dl in contrast with results of previous in vitro studies. Sustained glucose infusion was necessary to decrease APP levels from normal fed levels of 8-10 to 4-5 ng/ml within 3-5 min; bolus injection was without effect on APP levels even though plasma glucose levels reached 730 mg/dl. Neither phentolamine nor propranolol altered basal IRI, APP, or glucose levels. Phentolamine also was without effect on the glucose-induced rise in IRI or decrease in APP levels. However, propranolol pretreatment obtunded the usual glucose-induced IRI release concomitant with total blockage of the glucose-induced suppression of APP. It is concluded that chickens may be much more sensitive to glucose-induced insulin release in vivo than reported earlier and that adrenergic receptor regulation of IRI and APP release in the basal state is relatively unimportant. The beta receptor site appears stimulatory to glucose-induced insulin release, while being inhibitory to the glucose-induced depression normally observed in APP levels.