A Block in Epinephrine-induced Glycogenolysis in Hearts from Adrenalectomized Rats

Abstract

Abstract Perfused hearts from adrenal-deficient rats showed an impaired glycogenolytic response to suboptimal concentrations of epinephrine as judged by measurements of tissue glycogen and lactate production. The glycogenolytic response could be restored to normal by treatment of these animals with cortisol in vivo. Individual steps in the path of epinephrine-stimulated glycogenolysis were examined. Adrenalectomy did not impair adenosine 3',5'-monophosphate accumulation in response to several concentrations of epinephrine; a histone kinase, partially purified from hearts of adrenalectomized rats, was as sensitive to activation by adenosine 3',5'-monophosphate as the enzyme prepared from normal hearts; and the activation of phosphorylase b kinase by several concentrations of epinephrine was unaffected by the deficiency of adrenal cortical hormones. However, suboptimal concentrations of epinephrine did not activate phosphorylase in hearts from adrenalectomized rats to the normal extent. These findings suggest therefore that the defect following adrenalectomy lies in the activity of phosphorylase b kinase. The defect could be overcome by administration of adrenal glucocorticoid in vivo or by raising the perfusate calcium concentration.