Post-Exercise Insulin Sensitivity and Glucose Disposal are Unaffected by Intramuscular Triglyceride (IMTG) Levels

Abstract

PURPOSE The relationships between exercise, IMTGs and insulin sensitivity are still not fully understood. The aim of this study was, therefore, to determine the effects of acute (5 hr) vs. chronic (6 days of 1 hr/day) swimming exercise on whole-body insulin sensitivity and glucose disposal in male Wistar rats following 6 wk of high-fat (60% fat) feeding. METHODS 9-week old male Wistar rats were assigned to one of four treatment groups (high-fat fed chronic exercise, high-fat fed acute exercise, high-fat fed control, chow-fed control). Post-exercise, all animals fed ad libitum for 6–7 hr, before an overnight fast. Approximately 24 hr post-exercise, half of the animals from each group were randomly assigned to a euglycemic/hyperinsulinemic clamp to assess insulin sensitivity and 2- deoxyglucose uptake. IMTG levels and glycogen levels were also assessed. RESULTS Chronic exercise improved insulin sensitivity when compared to acute exercise (p= 0.03), while glycogen levels paralleled this improvement in insulin sensitivity. IMTG levels were not altered significantly, but there was a trend towards an increase in both exercise groups when compared to the high-fat fed control group (p = 0.06). IMTG values were identical between exercise groups and did not, therefore, parallel the changes in insulin sensitivity. CONCLUSIONS These data suggest that post-exercise, mechanisms other than IMTGs are the major factor in insulin sensitivity improvement. Improvements in oxidative capacity and mitochondrial function, which occur following chronic training, are likely to be involved in these changes.