Prevention of Insulin Resistance by Environmental Manipulation as Young Rats Mature

Summary

This study was initiated in an attempt to see if the insulin resistance associated with maturation in young rats could be prevented by environmental manipulation. Consequently, seven week-old rats were either housed in standard laboratory cages and fed a calorie-restricted diet or placed individually in exercise wheel cages and allowed to eat chow ad lib. A control group of rats was housed in standard laboratory cages from seven weeks to five months of age, and also allowed to eat chow ad lib. When studied at five months of age, the chow-fed rats weighed more (624 ± 8 g) than either the calorie restricted (479 ± 9 g) or exercise trained (485 ± 13 g) rats. Insulin action was compared in the three groups by assessing the steady-state serum glucose (SSSG) and insulin (SSSI) concentrations achieved during a continuous intravenous infusion of glucose and exogenous insulin. The results of these studies indicated that SSSG concentration was significantly higher (P < 0.001) in chow-fed rats than in the two experimental groups. Since SSSI concentrations were the same in all three groups, lower SSSG concentrations in calorie-restricted and exercise trained rats indicates that insulin-stimulated glucose uptake was preserved in these two groups as compared to the chow-fed population. In an attempt to understand why exercise training and calorie restriction prevented the development of insulin resistance, muscle glycogen synthase activity and muscle capillary density were compared in the three groups of five month-old rats. Although exercise-trained rats demonstrated an increase in both muscle glycogen synthase activity and muscle capillary density, there was no difference in these two variables between the chow-fed and calorie-restricted rats. Thus, both calorie restriction and exercise training can attenuate the insulin resistance associated with the maturation process in young rats. It appears that this is primarily due to the prevention of excessive weight gain, irrespective of how this is accomplished, and does not appear to be due to increases in either muscle glycogen synthase activity or capillary density.

Key-Words

Insulin Resistance - Capillary Density - Glycogen Synthase - Exercise Trained - Calorie Restricted