In vitro insulin secretion from the penguin (Pygoscelis papua) pancreas

In experiments performed at the Almirante Brown Scientific Station (64° 53′ South; 62° 53′ West), arginine induced in penguins significant release of insulin from incubated pieces of pancreas, while glucose acted as stimulus only at very high concentrations. Substances active on the adenyl cyclase system, such as glucagon, theophylline, isoproterenol, and even 3′,5′ cyclic AMP, stimulated insulin release. l -Propranolol inhibited isoproterenol-induced insulin release. Phentolamine, in the doses used, had no effect on either basal or isoproterenol-induced insulin secretion. Ouabain and glibenclamide failed to promote any change in the amount of insulin secreted. The results suggest that (a) in the penguin pancreas arginine rather than glucose may be a prominent stimulus for insulin secretion; (b) the penguin beta cell shows decreased sensitivity to glucose; (c) the adenyl cyclase system plays an important role in the mechanism(s) regulating insulin secretion; (d) under our experimental conditions, adrenergic modulation of insulin release is mediated chiefly through beta receptors.