Increased insulin suppression of plasma free fatty acid concentration in exercise-trained rats

The effect of exercise training on the insulin suppression of plasma free fatty acid (FFA) concentrations was studied in unanesthetized rats with the hyperinsulinemic-euglycemic clamp technique. Seven rats trained (TR) for 3 h/day by continuous swimming during 8 wk were compared with 6 untrained (UT) body weight-matched rats. Both TR and UT rats were submitted to an exercise swimming session 18 h before the clamp. A smaller mean diameter of adipocytes sampled from the epididymal fat depot was measured in TR animals. The total quantity of glucose infused to maintain euglycemia was 2.2 times higher in TR than in UT animals. No significant differences in plasma insulin concentrations were found between the two groups throughout the experiment. Insulin infusions resulted in a 60% decrease of plasma FFA in TR rats (mean value: from 0.46 to 0.18 mM) compared with 27% in UT animals (mean value: from 0.45 to 0.33 mM). The data indicate a greater ability of insulin to suppress plasma FFA levels with exercise training, which suggests an increased antilipolytic action of insulin in adipocytes under this condition.