Metabolic alterations induced by voluntary exercise and discontinuation of exercise in hamsters

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Abstract
A study was conducted to determine the possible biochemical mechanisms responsible for the rapid increase in body weight and body fat during the early phase of exercise-retirement. Thirty-two adult female hamsters were allotted to four groups of eight each. One group served as sedentary controls. Oner groups had access to voluntary disc-running during a 35-day period of the 76-day experimental period and were retired from running for 0, 8, and 41 days, respectively, before the termination of the experiment. Disc-running reduced body fat and body weight. Discontinuation of running led to a fast gain of body fat and body weight. Disc-running decreased serum triacylglycerol levels but had no effect on serum cholesterol levels. Serum high-density lipoprotein-cholesterol concentration was significantly elevated at 8 days after retirement but was not changed during exercise or at 41 days after retirement. Exercise or discontinuation of exercise had no effect on serum T-3 or T-4 levels. The rate of fatty acid synthesis and the activities of malic enzyme and fatty acid synthetase in the liver were increased during running and during the early phase of retirement. Liver glucose-6-phosphate dehydrogenase activity was increased at 8 days after discontinuation of running. Disc-running enhanced food intake which was not reduced to the sedentary level until about 10 days after retirement, suggesting a delay in adaptation to reduced energy expenditure. Results of the present study suggest that both the delay in food intake adaptation and the enhanced lipogenic activity play a role in the rapid gain of body weight and body fat during the early phase of exercise-retirement.