Effect of short-term exercise training on insulin-stimulated PI 3-kinase activity in human skeletal muscle.

The purpose of this study was to determine if the improvement in insulin sensitivity with exercise training is associated with enhanced phosphatidylinositol 3-kinase (PI 3-kinase) activity. Nine sedentary men were studied before and after 7 days of exercise training (1 h/day, ≈75% maximal oxygen consumption). Insulin sensitivity was determined with a euglycemic-hyperinsulinemic glucose clamp in the sedentary state and 15-17 h after the final exercise bout. PI 3-kinase activity was determined from samples (vastus lateralis) obtained in the fasted condition and after 60 min of submaximal insulin stimulation during the clamp. After exercise, glucose infusion rate increased ( P < 0.05) significantly (means ± SE, 7.8 ± 0.5 vs. 9.8 ± 0.8 mg ⋅ kg-1 ⋅ min-1), indicating improved insulin sensitivity. Insulin-stimulated (insulin stimulated/fasting) phosphotyrosine immunoprecipitable PI 3-kinase activity also increased significantly ( P < 0.05) with exercise (3.1 ± 0.8-fold) compared with the sedentary condition (1.3 ± 0.1-fold). There was no change in fasting PI 3-kinase activity. These data suggest that an enhancement of insulin signal transduction in skeletal muscle may contribute to the improvement in insulin action with exercise.