Role of the Sympathoadrenal System in the Regulation of Glycogen Metabolism in Resting and Exercising Skeletal Muscles

Summary

The purpose of the present study was to characterize the role of catecholamines in the regulation of skeletal muscle glycogen metabolism during exercise. Using the rat hindlimb perfusion technique we have measured skeletal muscle glycogen content, glycogen phosphorylase and synthase activities in sympathectomized and/or demedullated rats under epinephrine treatment (10^-7M) at rest and during muscle contraction. When epinephrine and/or norepinephrine deficiency was induced, muscle contraction resulted in a decrease in glycogen content (-63%) despite a decrease in glycogen phosphorylase activity ratio (0.25 to 0.11; p < 0.001) and an increase in glycogen synthase activity ratio (0.13 to 0.27; p < 0.001). Under these conditions, epinephrine treatment further reduced glycogen content while blunting the changes in the activity ratio of the rate-limiting enzymes. These data indicate that catecholamines do not play a primary role in skeletal muscle glycogen breakdown during acute exercise and suggest that allosteric regulators may be of prime importance.

Key words

Glycogen Metabolism - Sympathoadrenal System - Skeletal Muscle - Exercise - Glycogen Phosphorylase - Glycogen Synthase