Beta adrenergic receptors mediated effects, insulin and plasma free fatty acids in the duck

Beta-adrenergic blockade by IV propranolol treatment (5 mg/kg), resulted in an important drop in plasma immunoreactive insulin (IRI) in normal 24-hour fasted ducks, indicating that basal insulin secretion is controlled by beta-adrenergic receptors. Concomitantly plasma free fatty acids (FFA) are doubled; this effect is suppressed in animals made insulin-deficient by total pancreatectomy or hypophysectomy and in normal animals when the drop of plasma IRI is prevented by simultaneous administration of insulin. These results show that insulin, considered as devoid of any direct actin on lipolysis in birds, does play a role in plasma FFA regulation in the duck and confirm previous studies on totally pancreatectomized animals. This effect was also observed in fed animals in which propranolol, by decreasing plasma IRI to fasting levels, brings back plasma FFA to values observed in fasted ducks. Furthermore, propranolol, by impairing the hypoglycaemia of hypophysectomized or totally pancreatectomized animals suggest that effects mediated by beta-adrenergic receptors play a direct role in the regulation of plasma glucose level in the duck. Finally, glucose administration in propranolol treated animals show that the beta cell becomes insensitive to glucose in the absence of a normal beta adrenergic stimulation. This is not the case in A cell which remains responsive to hyper- and hypoglycaemia.