Role of adrenoceptors and cAMP on the catecholamine-induced inhibition of proteolysis in rat skeletal muscle

Abstract

The role of adrenoceptor subtypes and of cAMP on rat skeletal muscle proteolysis was investigated using a preparation that maintains tissue glycogen stores and metabolic activity for several hours. In both soleus and extensor digitorum longus (EDL) muscles, proteolysis decreased by 15–20% in the presence of equimolar concentrations of epinephrine, isoproterenol, a nonselective β-agonist, or clenbuterol, a selective β2-agonist. Norepinephrine also reduced proteolysis but less markedly than epinephrine. No change in proteolysis was observed when muscles were incubated with phenylephrine, a nonselective α-agonist. The decrease in the rate of protein degradation induced by 10−4 M epinephrine was prevented by 10−5 M propranolol, a nonselective β-antagonist, and by 10−5 M ICI 118.551, a selective β2-antagonist. The antiproteolytic effect of epinephrine was not inhibited by prazosin or yohimbine (selective α1-and α2-antagonists, respectively) or by atenolol, a selective β1-antagonist. Dibutyryl cAMP and isobutylmethylxanthine reduced proteolysis in both soleus and EDL muscles. The data suggest that catecholamines exert an inhibitory control of skeletal muscle proteolysis, probably mediated by β2-adrenoceptors, with the participation of a cAMP-dependent pathway.