Thermogenic property and its hormonal regulation in a South China field mouse, Apodemus draco, under seasonal acclimatization

Environmental factors, such as temperature, play an important role in the adjusting of body mass and thermogenesis in small mammals. In the present study, we examined thermogenic properties of a field mouse, Apodemus draco, under seasonal acclimatization. Body mass as well as several physiological, hormonal markers, and uncoupling-protein 1 (UCP1) contents were measured. The results showed that body mass decreased, while rest metabolic rate (RMR), non-shivering thermogensis (NST), energy intake and UCP1 contents increased in winter. Serum leptin level, tri-iodothyronine (T3), thyroxine (T4), T3/T4, testosterone and melatonin concentration showed seasonal variation, while thyroid-stimulating hormone (TSH) showed no difference between seasons. There were significant negative correlation between serum leptin level and RMR, NST, energy intake, UCP 1 contents and serum T3 (r= -0.496, P less than 0.05, r= -0.700, P less than 0.01, r= -0.641, P less than 0.01, r= -0.552, P less than 0.05, r= -0.536, P less than 0.05, respectively). Serum leptin level was positive correlated with body fat mass and T4 (r= 0.764; P less than 0.01, r= 0.484, P less than 0.05). However, no correlation was found between serum leptin level and serum TSH concentrations (r= 0.361, P greater than 0.05). The present results suggested that A. draco adapted to winter cold stress by increasing energy intake, thermogenesis and decreasing body mass and body fat mass. Leptin may act as a starvation signal to permit the increase in energy intake for energy expenditure mainly as thermogenesis for winter adaptation. Furthermore, testosterone and melatonin seem to be involved in the regulation of body mass and energy balance in A. draco.