Metabolic fuel homeostasis in Syrian hamsters: nycthemeral and exercise variables.

The food intake and growth of male and female golden hamsters, with and without access to running wheels, were measured under several conditions. These included different seasons, photoperiods and diets. Chow-fed males in wheels invariably had slowed weight gain and showed little hyperphagia relative to sedentary controls. One group of exercising female hamsters, fed high fat diet, grew faster than sedentary controls. The food intake of both exercising and sedentary groups was distributed evenly through the day/night cycle, but the exercising animals took smaller, more frequent meals at night. The nycthemeral variations in plasma glucose, triglycerides, free fatty acids and liver glycogen were quite small in sedentary hamsters. In exercising hamsters, however, liver glycogen was elevated in the late daytime and depleted in the mid-to-late night. In vivo lipogenesis rates in white and brown adipose and liver were elevated by day in the exercising compared to sedentary hamsters, and were lower at night in both groups. It appears that in exercising hamsters, and to a lesser extent sedentary hamsters, the day phase is one of inactivity and fuel storage, and the night phase is one of exercise and fuel mobilization.