Insulin Signaling and Glucose Uptake in the Soleus Muscle of 30-Month-Old Rats After Calorie Restriction With or Without Acute Exercise

Exercise and calorie restriction (CR) can each improve insulin sensitivity in older individuals, but benefits of combining these treatments on skeletal muscle insulin signaling and glucose uptake are poorly understood, especially in predominantly slow-twitch muscles (eg, soleus). Accordingly, our purpose was to determine independent and combined effects of prior acute exercise and CR (beginning at 14 weeks old) on insulin signaling and glucose uptake in insulin-stimulated soleus muscles of 30-month-old rats. CR alone (but not exercise alone) versus ad libitum sedentary controls induced greater insulin-stimulated glucose uptake. There was a main effect of diet (CR > ad libitum) for insulin-stimulated Akt^Ser473 and Akt^Thr308 phosphorylation. CR alone versus ad libitum sedentary increased Akt substrate of 160kDa (AS160) Ser⁵⁸⁸ phosphorylation and TBC1D1 Thr⁵⁹⁶, but not AS160 Thr⁶⁴² phosphorylation or abundance of GLUT4, GLUT1, or hexokinase II proteins. Combined CR and exercise versus CR alone did not further increase insulin-stimulated glucose uptake although phosphorylation of Akt^Ser473, Akt^Thr308, TBC1D1^Thr596, and AMPK^Thr172 for the combined group exceeded values for CR and/or exercise alone. These results revealed that although the soleus was highly responsive to a CR-induced enhancement of insulin-stimulated glucose uptake, the exercise protocol did not elevate insulin-stimulated glucose uptake, either alone or when combined with CR.