Physical activity prevented age-related decline in energy metabolism in genetically obese and diabetic rats, but not in control rats

Abstract

Laboratory rats are normally confined to cages that markedly restrict their physical activity. In these rats, the resting energy expenditure accounts for 90% of the total daily energy expenditure, while the daily physical activity in humans consumes 30% of the total daily energy expenditure. Otsuka Long Evans Tokushima Fatty (OLETF) rats have been developed as a model of non-insulin-dependent diabetes mellitus (NIDDM) with mild obesity, and obesity is an important factor that induces diabetes in this strain. We implemented a running-wheel exercise regimen that was the equivalent of normal physical activity to provide light exercise for OLETF rats. The purpose of the study was to determine if light exercise improves the age-related decline in energy metabolism and glucose intolerance in OLETF rats. The effects were also compared in control Long Evans Tokushima (LETO) rats. From 12 to 46 weeks of age, the rats performed a running-wheel exercise (3000 m/day). Energy metabolism was determined at 8-week intervals. The typical increase in body weight was significantly decreased in OLETF rats in response to exercise, while no significant effect was observed in LETO rats. Energy expenditure and basal metabolic rate (BMR) per kilogram body weight (not whole-body weight) were increased by exercise in OLETF rats, but not in LETO rats. At 46 weeks of age, after exercise, the blood glucose and hemoglobin (Hb)A1c levels, as well as the plasma levels of insulin, triglyceride, cholesterol, and leptin significantly decreased in OLETF rats, while only the plasma levels of cholesterol and leptin significantly decreased in LETO rats. Light exercise thus appears to be beneficial for preventing age-related decline in energy metabolism and glucose intolerance in OLETF rats.