Alpha and Beta adrenergic effects on metabolism in contracting, perfused muscle

Abstract

The role of α- and β-adrenergic receptor stimulation for the effect of epinephrine on muscle glycogenolysis, glucose- and oxygen uptake and muscle performance was studied in the perfused rat hindquarter at rest and during electrical stimulation (60 contractions/min). Adrenergic stimulation was obtained by epinephrine in a physiological concentration (2.4 × 10^-8 M) and α- and β-adrenergic blockade by 10^-5 M phentolamine and propranolol, respectively. Epinephrine enhanced net glycogenolysis during contractions most markedly in slow-twitch red fibers. In these fibers the effect was mediated by α- as well as by β-adrenergic stimulation, the latter involving production of cAMP, phosphorylase activation and synthase inactivation. In contrast, in fast-twitch fibers only β-adrenergic mechanisms were involved in the glycogenolytic effect of epinephrine. Moreover, inactivation of synthase was less in these fibers. Epinephrine also increased the net release of lactate from the hindquarter, an effect abolished by combined α- and β-adrenergic blockade but by neither α- nor β-adrenergic blockade alone. Epinephrine increased uptake of oxygen and glucose by stimulation of α-adrenergic receptors and had a positive inotropic effect during contractions which was abolished by α- as well as by β-adrenergic blockade. The results indicate that epinephrine has profound effects on contracting muscle, and that these effects are elicited through different combinations of α- and β-adrenergic receptor stimulation.