Body weight, food intake and energy regulation in exercising and melatonin-treated Siberian hamsters.

The coupling among energy intake, storage, and expenditure was examined in male Siberian hamsters (Phodopus sungorus sungorus) given access to running wheels for 14 weeks. Half of the hamsters were injected with melatonin in a schedule that mimics the effects of short photoperiods by decreasing body weight, carcass lipid content, and testis weight. The exercise-induced body weight increases which are seen in Syrian hamsters (Mesocricetus auratus) were not found in Siberian hamsters. Instead, the Siberian hamsters maintained their body weights, compensating for the increased energy demands of exercise by increasing their food intakes. Exercise did not affect carcass composition. Melatonin treatment decreased food intake and carcass lipid stores but did not affect voluntary exercise. The previously reported decrease in testis weight was seen in all melatonin-treated hamsters, but the stimulation of brown adipose tissue growth was not. Thus, exercising Siberian hamsters, unlike exercising Syrian hamsters, appear to exhibit a tight coupling among energy intake, storage, and expenditure.