School of Agricultural Science, Liaocheng University, Liaocheng, Shandong, 252059, China.
J Exp Biol. 2010 Dec 1;213(Pt 23):3988-97. doi: 10.1242/jeb.046821.
The limitation on sustainable energy intake (SusEI) is important because it establishes the upper energetic limit on the ability of animals to disperse, survive and reproduce. However, there are still arguments about what factors impose that limitation. Thermoregulation in cold environments imposes great energy demands on small mammals. A cold-exposed animal has been suggested to be a model suitable for testing these factors. Here, we examined the changes in food intake and digestible energy intake (DEI) as measures of SusEI, thermogenic capacity and behavioral patterns in Swiss mice exposed to consecutively lower ambient temperatures from 23 to -15°C. Cold-exposed mice showed significant decreases in body mass, fat content of the carcass and body temperature, and increases in DEI compared with controls. The time spent on feeding significantly increased with decreasing temperatures, and time spent on general activity decreased following cold exposure. Resting metabolic rate, nonshivering thermogenesis and serum tri-iodothyronine levels significantly increased in mice exposed to lower temperatures in comparison with controls, whereas these thermogenic variables were not significantly different between 0 and -15°C. It might suggest that SusEI in cold exposed Swiss mice was constrained peripherally by the capacity to produce heat and also by the ability to dissipate body heat, but to a different extent. Moderate cold exposure might result in a relaxation of the heat dissipation limit (HDL), allowing the animals to increase food intake to meet cold stress. When animals are exposed to severe cold, the thermogenenic capacity might reach a ceiling, failing to compensate for the heat loss and which would finally result in lower body temperature and considerable weight loss. This might indicate that the HDL was set at a higher level than peripheral limits for Swiss mice exposed to a consecutive decrease in ambient temperatures.
可持续能量摄入（SusEI）的限制很重要，因为它确定了动物扩散、生存和繁殖的能量上限。然而，关于是什么因素限制了这一点，仍然存在争议。在寒冷环境中，体温调节会对小型哺乳动物造成巨大的能量需求。有人认为，暴露在寒冷环境中的动物是测试这些因素的合适模型。在这里，我们检查了食物摄入量和可消化能量摄入量（DEI）的变化，作为 SusEI、产热能力和行为模式的衡量标准，这些瑞士小鼠在 23 至-15°C 的连续降低环境温度下暴露。与对照组相比，寒冷暴露的小鼠体重、胴体脂肪含量和体温显著下降，DEI 增加。随着温度的降低，用于进食的时间显著增加，而一般活动时间在寒冷暴露后减少。与对照组相比，暴露于较低温度的小鼠静息代谢率、非颤抖产热和血清三碘甲状腺氨酸水平显著增加，而在 0 和-15°C 之间，这些产热变量没有显著差异。这可能表明，在寒冷暴露的瑞士小鼠中，SusEI 受到产生热量的能力和散发身体热量的能力的限制，但程度不同。适度的寒冷暴露可能导致散热限制（HDL）放松，允许动物增加食物摄入以应对寒冷压力。当动物暴露于严寒时，产热能力可能达到上限，无法弥补热量损失，最终导致体温下降和体重明显减轻。这可能表明，与连续降低环境温度下的瑞士小鼠相比，HDL 的设定水平高于外周限制。
