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

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 beta-agonist, or clenbuterol, a selective beta(2)-agonist. Norepinephrine also reduced proteolysis but less markedly than epinephrine. No change in proteolysis was observed when muscles were incubated with phenylephrine, a nonselective alpha-agonist. The decrease in the rate of protein degradation induced by 10(-4) M epinephrine was prevented by 10(-5) M propranolol, a nonselective beta-antagonist, and by 10(-5) M ICI 118.551, a selective beta(2)-antagonist. The antiproteolytic effect of epinephrine was not inhibited by prazosin or yohimbine (selective alpha(1)-and alpha(2)-antagonists, respectively) or by atenolol, a selective beta(1)-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 beta(2)-adrenoceptors, with the participation of a cAMP-dependent pathway.