Phentolamine activation of glycogenolysis in rat skeletal muscle

Abstract

Administration of phentolamine to the rat or dog increases significantly the concentration of blood lactic acid, and reduces blood glucose. In the rat, the lacticacidemia appears due to an activation of glycogenolysis in skeletal muscle, since phentolamine administration results in an increase in phosphorylase a and a reduction of the glycogen content of this tissue. The plasma concentration of catecholamines also increases suggesting that phentolamine elicits these metabolic effects through their release. The phentolamine-induced changes in the blood lactic acid, phosphorylase a and glycogen content of skeletal muscle can be inhibited by pretreating the rat with the adrenergic blocking drugs, butoxamine or 4-(2-isopropyl-1-hydroxyethyl)methane-sulfonanilide (MJ1999). The phentolamine-induced lacticacidemia is inhibited partially if the rat is pretreated with guanethidine or reserpine; it is reduced markedly in the adrenal demedullated rat, and is eliminated if guanethidine is administered to the adrenal demedullated rat prior to phentolamine. The results suggest that phentolamine activates glycogenolysis in rat skeletal muscle, and this activation is mediated by the catecholamines.