Effect of confinement in small space flight size cages on insulin sensitivity of exercise-trained rats

Previous studies on men under conditions of total bed rest, and laboratory animals under limited physical activity, have shown resistance to insulin-induced glucose uptake and, conversely, increased sensitivity to insulin with exercise training. To determine whether the beneficial effects of exercise training on increasing insulin sensitivity are lost following end of exercise and confinement in small cages, oral glucose tolerance tests (OGTT) were given to control and exercise-trained rats before and after placement in small space flight size cages (11 X 4 X 4 1/2 in) for 7 d. The product of the area of the insulin and glucose curves of the OGTT (IG index) provides a measure of insulin resistance. Values obtained, before confinement, were one-half as high in exercise-trained rats as those in control rats (p less than 0.001), reflecting increased sensitivity to insulin with exercise training. After 7 d confinement, the IG index was not significantly different from initial values for both control and exercise-trained rats. These findings indicate that increased insulin sensitivity in exercise-trained rats persists 7 d after cessation of running activity. Furthermore, the data suggest that exercise training, before flight, may be beneficial in minimizing the loss of insulin sensitivity expected with decreased use of gravity dependent muscles during exposure to hypogravity in space flight.