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 (KCl) infusion, however, is not suppressed; in fact, in ureter-ligated dogs simultaneously infused with 360 microgram. epinephrine per hour and 2 mEq. KCl 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 KCl infusion, with and without epinephrine. It is unlikely that KCl, 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.