Severe diabetes prohibits elevations in muscle protein synthesis after acute resistance exercise in rats

This study determined whether rates of protein synthesis increase after acu te resistance exercise in skeletal muscle from severely diabetic rats. Prev ious studies consistently show that postexercise rates of protein synthesis are elevated in nondiabetic and moderately diabetic rats. Severely diabeti c rats performed acute resistance exercise (n = 8) or remained sedentary (n = 8). A group of nondiabetic age-matched rats served as controls (n = 9). Rates of protein synthesis were measured 16 h after exercise. Plasma glucos e concentrations were >500 mg/dl in the diabetic rats. Rates of protein syn thesis (nmol phenylalanine incorporated . g muscle(-1) . h(-1), means +/- S E) were not different between exercised (117 +/- 7) and sedentary (106 +/- 9) diabetic rats but were significantly (P < 0.05) lower than in sedentary nondiabetic rats (162 +/- 9) and in exercised nondiabetic rats (197 +/- 7). Circulating insulin concentrations were 442 +/- 65 pM in nondiabetic rats and 53 +/- 11 and 72 +/- 19 pM in sedentary and exercised diabetic rats, re spectively. Plasma insulin-like growth factor I concentrations were reduced by 33% in diabetic rats compared with nondiabetic rats, and there was no d ifference between exercised and sedentary diabetic rats. Muscle insulin-lik e growth factor I was not affected by resistance exercise in diabetic rats. The results show that there is a critical concentration of insulin below w hich rates of protein synthesis begin to decline in vivo. In contrast to pr evious studies using less diabetic rats, severely diabetic rats cannot incr ease rates of protein synthesis after acute resistance exercise.