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

摘要：

食物资源的不确定性是动物在自然环境中面临的重要挑战之一。“代谢率转换”假说认为，动物应对食物短缺的能量学策略在于降低代谢率以减少能量支出。然而在不同环境温度下非冬眠小型哺乳动物应对食物短缺的“代谢率转换”策略，尚不明确。为探究这一问题，将成年雄性黑线仓鼠在低温 (5.0℃)、室温 (21.0℃) 和高温 (32.5℃) 下断食处理24 h、36 h和48 h，再恢复自由取食 (重喂食) 5周。以植入式i-button测定腹腔体温，以开放式氧气分析系统测定代谢率、静息代谢率 (RMR) 和非颤抖性产热 (NST)，以放射性免疫技术测定血清三碘甲腺原氨酸 (T₃) 和四碘甲状腺原氨酸 (T₄) 浓度。结果发现，与32.5℃组相比，5.0℃和21.0℃组断食后体温显著降低。断食组和重喂食组昼间和夜间代谢率、RMR和NST在低温下显著增加，高温下显著降低，然而断食组与重喂食组之间无显著差异。断食组黑线仓鼠脂肪贮存显著减少，环境温度越低脂肪动员越迅速。重喂食后脂肪贮存显著增加，但低温抑制脂肪贮存。断食组和重喂食组血清T₃和T₄水平无显著差异，但受环境温度的影响，低温下显著增加，与代谢产热的变化相一致。结果表明，不同温度下经历食物短缺的黑线仓鼠维持较高代谢率，不符合“代谢率转换”假说；低温下较高的代谢率主要用于满足体温调节的能量需求，甲状腺激素对代谢产热的促进作用是其内在机制之一。

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