Activation of muscle phosphorylase by subcutaneously injected epinephrine as related to other metabolic changes in vivo

Abstract

Gastrocnemius muscle was quickly excised from the rat 30 min after subcutaneous injection of epinephrine and the tissue was extracted with 60% glycerol and analyzed for phosphorylase a content and the ratio of active to inactive form of phosphorylase b kinase. The subcutaneous injection of epinephrine into fasted rats was without effect on both enzyme activities, whereas epinephrine administration into glucose-fed rats or streptozotocin-diabetic rats caused a significant formation of the active forms of both phosphorylase and phosphorylase b kinase. Feeding of glucose and induction of diabetes produced lower control ratios of the active to the inactive form for both enzymes with an inverse correlation with blood levels of glucose and lactate. The lower the control activity, the more activation elicited by epinephrine. When both enzymes were assayed in the protein-glycogen complex, activation by epinephrine was detected even in muscle of the normal rat receiving neither glucose nor streptozotocin. These findings in vivo are interpreted as support for the concept that breakdown of muscle glycogen is induced by subcutaneously injected epinephrine via activation of phosphorylase b kinase and phosphorylase, although there is no conclusive evidence that the enzymes are really activated in normal fasted rats.