Geiser Fritz
Zoology, Center for Behavioural and Physiological Ecology, University of New England, Armidale, NSW Australia 2351.
Annu Rev Physiol. 2004;66:239-74. doi: 10.1146/annurev.physiol.66.032102.115105.
Although it is well established that during periods of torpor heterothermic mammals and birds can reduce metabolic rates (MR) substantially, the mechanisms causing the reduction of MR remain a controversial subject. The comparative analysis provided here suggests that MR reduction depends on patterns of torpor used, the state of torpor, and body mass. Daily heterotherms, which are species that enter daily torpor exclusively, appear to rely mostly on the fall of body temperature (Tb) for MR reduction, perhaps with the exception of very small species and at high torpor Tb, where some metabolic inhibition may be used. In contrast, hibernators (species capable of prolonged torpor bouts) rely extensively on metabolic inhibition, in addition to Tb effects, to reduce MR to a fraction of that observed in daily heterotherms. In small hibernators, metabolic inhibition and the large fall of Tb are employed to maximize energy conservation, whereas in large hibernators, metabolic inhibition appears to be employed to facilitate MR and Tb reduction at torpor onset. Over the ambient temperature (Ta) range where torpid heterotherms are thermo-conforming, the Tb-Ta differential is more or less constant despite a decline of MR with Ta; however, in thermo-regulating torpid individuals, the Tb-Ta differential is maintained by a proportional increase of MR as during normothermia, albeit at a lower Tb. Thermal conductance in most torpid thermo-regulating individuals is similar to that in normothermic individuals despite the substantially lower MR in the former. However, conductance is low when deeply torpid animals are thermo-conforming probably because of peripheral vasoconstriction.
尽管早已明确，在蛰伏期变温哺乳动物和鸟类能够大幅降低代谢率（MR），但导致代谢率降低的机制仍是一个存在争议的话题。此处提供的比较分析表明，代谢率降低取决于所采用的蛰伏模式、蛰伏状态和体重。每日蛰伏动物，即仅进入每日蛰伏状态的物种，似乎主要依靠体温（Tb）下降来降低代谢率，不过非常小的物种以及处于高蛰伏体温时可能除外，在这些情况下可能会利用一些代谢抑制作用。相比之下，冬眠动物（能够进行长时间蛰伏的物种）除了体温影响外，还广泛依靠代谢抑制作用，将代谢率降低至每日蛰伏动物所观察到的代谢率的一小部分。在小型冬眠动物中，利用代谢抑制作用和大幅体温下降来最大限度地保存能量，而在大型冬眠动物中，代谢抑制作用似乎是在蛰伏开始时用于促进代谢率和体温降低。在蛰伏变温动物与环境温度（Ta）呈热顺应关系的温度范围内，尽管代谢率随环境温度下降，但体温与环境温度的差值或多或少保持恒定；然而，在进行体温调节的蛰伏个体中，如同在正常体温时一样，通过代谢率按比例增加来维持体温与环境温度的差值，尽管体温较低。大多数处于蛰伏体温调节状态的个体的热传导率与正常体温个体相似，尽管前者的代谢率要低得多。然而，深度蛰伏动物处于热顺应状态时热传导率较低，可能是由于外周血管收缩所致。
