Hypertrophy of skeletal muscle in diabetic rats in response to chronic resistance exercise

Abstract

This study had the following objectives: 1) to determine whether diabetic rats could increase muscle mass due to a physiological manipulation (chronic resistance exercise), 2) to determine whether exercise training status modifies the effect of the last bout of exercise on elevations in rates of protein synthesis, and 3) to determine whether chronic resistance exercise alters basal glycemia. Groups consisted of diabetic or nondiabetic rats that performed progressive resistance exercise for 8 wk, performed acute resistance exercise, or remained sedentary. Arterial plasma insulin in diabetic groups was reduced by about one-half ( P < 0.05) compared with nondiabetic groups. Soleus and gastrocnemius-plantaris complex muscle wet weights were lower because of diabetes, but in response to chronic exercise these muscles hypertrophied in diabetic (0.028 ± 0.003 vs. 0.032 ± 0.0015 g/cm for sedentary vs. exercised soleus and 0.42 ± 0.068 vs. 0.53 ± 0.041 g/cm for sedentary vs. exercised gastrocnemius-plantaris, both P < 0.05) but not in nondiabetic (0.041 ± 0.0026 vs. 0.042 ± 0.003 g/cm for sedentary vs. exercised soleus and 0.72 ± 0.015 vs. 0.69 ± 0.013 g/cm for sedentary vs. exercised gastrocnemius-plantaris) rats when muscle weight was expressed relative to tibial length or body weight (data not shown). Another group of diabetic rats that lifted heavier weights showed muscle hypertrophy. Rates of protein synthesis were higher in red gastrocnemius in chronically exercised than in sedentary rats: 155 ± 11 and 170 ± 7 nmol phenylalanine incorporated ⋅ g muscle−1 ⋅ h−1in exercised diabetic and nondiabetic rats vs. 110 ± 14 and 143 ± 7 nmol phenylalanine incorporated ⋅ g muscle−1 ⋅ h−1in sedentary diabetic and nondiabetic rats. These elevations, however, were lower than in acutely exercised (but untrained) rats: 176 ± 15 and 193 ± 8 nmol phenylalanine incorporated ⋅ g muscle−1 ⋅ h−1in diabetic and nondiabetic rats. Finally, chronic exercise training in diabetic rats was associated with reductions in basal glycemia, and such reductions did not occur in sedentary diabetic groups. These data demonstrate that, despite lower circulating insulin concentrations, diabetic rats can increase muscle mass in response to a physiological stimulus.