Role of glycogen concentration and epinephrine on glucose uptake in rat epitrochlearis muscle

The effects of diet-manipulated variations in muscle glycogen concentration and epinephrine on glucose uptake were studied in epitrochlearis muscles from Wistar rats. Both basal and insulin-stimulated glucose uptake {measured with a tracer amount of 2-[1,2-H-3(N)]deoxy-D-glucose} inversely correlated with initial glycogen concentration (glycogen concentration vs. basal glucose uptake: Spearman's rho = -0.76, n = 84, P < 0.000001; glycogen concentration vs. insulin-stimulated glucose uptake: Spearman's rho = -0.67, n = 44, P < 0.00001). Two fasting-refeeding procedures were used that resulted in differences in muscle glycogen concentrations, although with similar treatment for the last 48 h before the experiment. In the rats with the lower glycogen concentration, basal as well as insulin-stimulated glucose uptake was elevated. The muscle glycogen concentration had no effect on epinephrine-stimulated glycogenolysis. Epinephrine, however, was found to reduce basal glucose uptake in all groups. These results suggest that I)the glycogen concentration participates in the regulation of both basal and insulin-stimulated glucose uptake in skeletal muscle, 2) the magnitude of epinephrine-stimulated glycogen breakdown is independent of the glycogen concentration, and 3) epinephrine inhibits basal glucose uptake at all glycogen concentrations.