关键词: 脂肪贮存, 食物短缺, 代谢率, 黑线仓鼠, 温度, 甲状腺激素

Abstract:

Food availability is one of the most important problems for animals in natural environments. The ‘metabolic rate conversion’ hypothesis suggests that animals can decrease their metabolic rate to reduce energy expenditure, which is an important energy strategy for coping with food shortage. However, the ‘metabolic rate conversion’ strategy of the non-hibernating small mammals to cope with food shortage at different ambient temperatures remains uncertain. To address this issue, adult male striped hamsters were deprived of food for 24 h, 36 h and 48 h, at cold (5.0℃), room (21.0℃) and high temperatures (32.5℃) and then refed ad libitum for 5 weeks. Abdominal temperature was measured using implanted i-button. The metabolic rate, resting metabolic rate (RMR) and nonshivering thermogenesis (NST) were determined using open oxygen analysis system. Serum T₃ and T₄ levels were determined using radioimmunoassay technology. The results showed that body temperature significantly decreased at 5.0℃ and 21.0℃ following food deprivation compared to that at 32.5℃. The average metabolic rate over day and night, RMR, and NST significantly increased at cold temperature, and decreased at hot temperature, whereas they did not differ significantly between the groups of food deprivation and refeeding. The fat deposit significantly decreased following food deprivation, during which the rate of fat mobilization was higher at cold temperature than that at hot temperature. The fat deposit significantly increased following refeeding, which was considerably inhibited at cold temperature compared to that at hot temperature. The T₃ and T₄ levels did not significantly differ between the groups of food deprivation and refeeding. Consistent with the changes in metabolic rate, serum T₃ and T₄ levels were significantly affected by temperature, with increasing at cold temperature relative to that at hot temperature. It suggests that the striped hamsters have a similar metabolic rate at different temperatures during food shortage to that during refeeding period, inconsistent with the ‘metabolic rate conversion’ hypothesis. The food-deprived striped hamsters have higher metabolic rate at cold temperature to meet the energy requirements of body temperature regulation, within which the roles of thyroid hormones in stimulating heat production would be one of the most important mechanisms.

Key words: Fat deposit, Food shortage, Metabolic rate, Striped hamster, Temperature, Thyroid hormones