Effect of muscle glycogen depletion on in vivo insulin action in man

Abstract

In rats, muscle glycogen depletion has been associated with increased insulin action. Whether this also occurs in man has not been reported. After 4 d rest, 13 males (E Group) had a percutaneous muscle biopsy of the vastus lateralis muscle followed by a euglycemic clamp at plasma insulin congruent to 100 microU/ml and congruent to 1,900 microU/ml, with simultaneous indirect calorimetry. This was repeated 1 wk later, but after glycogen-depleting exercise the night before the euglycemic clamp. Seven subjects underwent the same protocol but were also re-fed 100 g carbohydrate (CHO) after the exercise (EF group). In both groups, the mean muscle glycogen content was approximately 40% lower (P less than 0.01) after exercise compared with the muscle glycogen content measured after rest. In the E group, the mean muscle glycogen synthase activity (percent independent of glucose-6-phosphate) increased threefold (P less than 0.001) after exercise, but increased only twofold in the EF group (P less than 0.02 between groups). In both groups, the mean basal and insulin-stimulated CHO oxidation rates were lower in the post-exercise, glycogen-depleted condition compared with the rested, glycogen-replete condition. The mean insulin-stimulated CHO storage rate increased significantly in the E group after exercise but not in the EF group. In the E group, the total insulin-stimulated CHO disposal rate (M) was 17 (P less than 0.04) and 10% (P less than 0.03) higher after exercise during the low and high dose insulin infusion, respectively. No significant changes in M were observed in the EF group. For all subjects, after rest and exercise, the M correlated with the CHO storage rates during the low (r = 0.80, P less than 0.001) and high dose (r = 0.77, P less than 0.001) insulin infusions. After exercise, the muscle glycogen synthase activity correlated with the CHO storage rate (r = 0.73, P less than 0.002; r = 0.75, P less than 0.002) during the low and high dose insulin infusions, respectively, and also with M (r = 0.64, P less than 0.008; r = 0.57; P less than 0.02).