Adrenal Corticosteroids and the Response to Epinephrine or Electrical Stimulation of the Enzymes of Glycogen Metabolism in Rat Skeletal Muscle

Previous studies have shown that epinephrine administration to adrenalectomized rats does not elicit conversion from the b to the a form of skeletal muscle glycogen phosphorylase (α-1,4-glucan:orthophosphate glucosyltransferase, EC 2.4.1.1) to the same extent as in normal animals. Extension of these results has shown that while conversion from the I to the D form of glycogen synthetase (UDP-glucose:glycogen α-4-glucosyltransferase, EC 2.4.1.11) is also impaired in adrenalectomized rats, conversion of phosphorylase b kinase (ATP:phosphorylase phosphotransferase, EC 2.7.1.37) from the nonactivated to the activated form (pH 6.8:8.2 ratio of activities) is unaffected by the deficiency of adrenal corticoid hormones. Administration of hydrocortisone or deoxycorticosterone restores the normal response of both glycogen Phosphorylase and synthetase to epinephrine. Tetanic electrical stimulation in vivo brings about conversion of phosphorylase b to a and of synthetase I to D, even in adrenalectomized rats. These findings suggest that the defect due to adrenalectomy does not lie in a decreased amount of one of the converting enzymes, but rather in some factor(s) governing the activity of one (or more) of them. ACKNOWLEDGMENTS The authors wish to express their gratitude to Marta M. Hernandez for skillful help in the course of this work, and to the members of the Instituto de Investigaciones Bioquímicas for advice and criticism.