Epinephrine Enhancement of Potassium-stimulated Immunoreactive Insulin Secretion Role of Beta-adrenergic Receptors

Although epinephrine stimulates insulin release by activation of beta-adrenergic receptors, its dominant effect (mediated by stimulation of alpha-adrenergic receptors) is an inhibition of insulin secretion that is powerful enough to suppress the secretory activity of insulin's most potent stimulants. The insulin-secretory response to potassium chloride (KC1) infusion, however, is not suppressed; in fact, in ureter-ligated dogs simultaneously infused with 360 μg. epinephrine per hour and 2 mEq. KC1 per kilogram per hour, insulin release is actually increased about threefold (over controls). Propranolol blockade of beta-adrenergic receptors essentially abolishes the insulin response to KCI infusion, with and without epinephrine. It is unlikely that KCI, like epinephrine, provokes insulin release by direct stimulation of the beta-adrenergic receptors of the beta cells of the pancreatic islets. However, potassium in some way enhances the beta adrenergic (secretory) activity of epinephrine and blunts its usually dominant alpha-adrenergic (inhibitory) effect.