Alterations in glucose and protein metabolism in animals subjected to simulated microgravity.

Reduction of physical activity due to disease or environmental restraints, such as total bed rest or exposure to spaceflight, leads to atrophy of skeletal muscle and is frequently accompanied by alterations in food intake and the concentration of metabolic regulatory hormones such as insulin. Hindlimb suspension of laboratory rats, as a model for microgravity, also shows marked atrophy of gravity dependent muscles along with a reduced gain in body weight. Suspended rats exhibit enhanced sensitivity to insulin-induced glucose uptake when compared with normal control rats and resistance to insulin action when compared with control rats matched similarly for reduced body weight gain.

Effect of body weight gain on insulin sensitivity after retirement from exercise training.

The objectives of this study were to determine how long increased insulin sensitivity, elicited by exercise training, persists after the end of training and what the effect of weight gain is on this retention. Exercise-trained (ET) rats ran voluntarily in freely rotating wheel cages, and insulin sensitivity was assessed by oral glucose tolerance tests (OGTT) and insulin suppression tests (IST). After training, ET rats were retired for 1, 3, or 7 days (R1, R3, or R7).

The effect of exercise training on insulin resistance in sedentary year old rats.

The purpose of this study was to determine if exercise training of 12-month-old Sprague-Dawley rats could reverse the resistance to insulin-induced glucose uptake that has been shown to occur in these animals. Twelve-month-old rats were trained to run 1 1/2 miles/day in motorized exercise wheel cages, and the ability of insulin to stimulate glucose uptake in these rats was compared with values observed in two groups of similar aged sedentary rats--one fed rat chow ad libitum and the other a calorie-restricted diet for 4 months. Body weight increased and insulin-stimulated glucose uptake decreased as rats fed chow ad libitum grew from 12 to 16 months of age.

Spontaneous running activity in male rats: effect of age.

Alterations in the intensity and pattern of spontaneous running activity as rats increase in age from 7 wk to 1 yr was studied in male rats placed in exercise wheel cages. Daily running records were obtained on 27 rats for periods up to 12 mo, and 24-h activity recordings were made of selected runners to study the variation in activity during the day. The data indicate that for rats running over 2,940 revolutions (or 2 miles/day), the maximum intensity of running attained can be divided into a group of high achievers (approximately 8 miles/day) and moderate achievers (averaging 4.

Causes of the triglyceride-lowering effect of exercise training in rats.

Serum triglyceride (TG) levels are lower in exercise-trained (ET) compared with control rats throughout a 24-h period (P less than 0.01-0.001).