Interactive Effects of Exercise and Insulin on Glycogen Storage in Different Muscle Groups

Abstract

Skeletal muscle is the primary site of glycogen storage. Different muscle groups consist of various portions of muscle fiber types, and different muscle fiber types exhibit varied capacities of glycogen synthesis and storage. Although swimming exercise has been used to study skeletal muscle metabolism in rats for years, it remains unclear that the acute effect of swimming exercise on glycogen utilization and replenishment in different muscle groups in rats. PURPOSE: To investigate the interactive effects of insulin and carbohydrate supplement on postexercise glycogen replenishment in different skeletal muscle groups. METHODS: Thirty-two male Sprague Dawley rats were weight-matched and assigned to the following four groups, including 1) sedentary control group (C), 2) sedentary rats with carbohydrate supplement (2 g/kg body wt), insulin administration (0.5 U/kg body wt) and 16 hours recovery (I), 3) swimming exercise with carbohydrate supplement and 16 hour recovery (E16), and 4) swimming exercise with carbohydrate supplement, insulin administration and 16 hours recovery (IE16). The swimming exercise protocol included two sessions of 3 hours continuous swimming, and two swimming sessions were separated by a 45 min rest. The insulin and carbohydrate supplements were given to the rats immediately after the second swimming session. After completion of exercise or recovery, the soleus (S), plantaris (P), quadriceps (Q), gastrocenimus (G) were surgically excised for evaluating muscular glycogen utilization and replenishment. RESULTS: For the C group, the amount of glycogen was significantly higher in G than that in S, P, and Q (55.1±2.05 v.s. 36.0±2.15, 26.4±1.3 & 22.0±1.07 μmol/g, p<.05). Glycogen replenishment was higher in S than that in P, Q and S for E16 group. For I group, glycogen replenishment was not different in all muscle groups. However, for IE16 group, the muscular glycogen replenishments in S and P were markedly increased than those in Q and G. CONCLUSION: The main finding of this study is that soleus had the highest rate of insulin-stimulated glycogen storage during post-exercise recovery in the analyzed muscle groups.