Nelson O Lynne, Robbins Charles T
Department of Veterinary Clinical Sciences, Washington State University, 100 Grimes Way, Pullman, WA, 99164, USA,
J Comp Physiol B. 2015 Apr;185(3):265-79. doi: 10.1007/s00360-014-0881-5. Epub 2014 Dec 27.
Mammalian hibernation has intrigued scientists due to extreme variations in normal seasonal physiological homeostasis. Numerous species manifest a hibernation phenotype although the characteristics of the hypometabolic state can be quite different. Ground squirrels (e.g., Sciuridae) are often considered the prototypical hibernator as individuals in this genus transition from an active, euthermic state (37 °C) to a nonresponsive hibernating state where torpid body temperature commonly falls to 3-5 °C. However, the hibernating state is not continuous as periodic warming and arousals occur. In contrast, the larger hibernators of genus Ursus are less hypothermic (body temperatures decline from approximately 37°-33 °C), are more reactive, and cyclical arousals do not occur. Both species dramatically reduce cardiac output during hibernation from the active state (bears ~75 % reduction in bears and ~97 % reduction in ground squirrels), and both species demonstrate hypokinetic atrial chamber activity. However, there are several important differences in cardiac function between the two groups during hibernation. Left ventricular diastolic filling volumes and stroke volumes do not differ in bears between seasons, but increased diastolic and stroke volumes during hibernation are important contributors to cardiac output in ground squirrels. Decreased cardiac muscle mass and increased ventricular stiffness have been found in bears, whereas ground squirrels have increased cardiac muscle mass and decreased ventricular stiffness during hibernation. Molecular pathways of cardiac muscle plasticity reveal differences between the species in the modification of sarcomeric proteins such as titin and α myosin heavy chain during hibernation. The differences in hibernation character are likely to account for the alternative cardiac phenotypes and functional strategies manifested by the two species. Molecular investigation coupled with better knowledge of seasonal physiological alterations is dramatically advancing our understanding of small and large hibernators and their evolutionary differences.
哺乳动物的冬眠现象一直吸引着科学家，因为其正常的季节性生理稳态会出现极端变化。尽管低代谢状态的特征可能大不相同，但许多物种都表现出冬眠表型。地松鼠（如松鼠科）常被视为典型的冬眠动物，因为该属的个体从活跃的、体温正常的状态（37℃）转变为无反应的冬眠状态，此时体温通常降至3 - 5℃。然而，冬眠状态并非持续不断，期间会有周期性的升温与苏醒。相比之下，熊属的大型冬眠动物体温降低幅度较小（体温从约37℃降至33℃），反应更灵敏，且不会出现周期性苏醒。两种动物在冬眠期间的心脏输出量均较活跃状态大幅降低（熊降低约75%，地松鼠降低约97%）且心房活动均减弱。然而，在冬眠期间，两组动物的心脏功能存在一些重要差异。熊在不同季节的左心室舒张充盈量和每搏输出量并无差异，但在冬眠期间，舒张期和每搏输出量的增加是地松鼠心脏输出量的重要贡献因素。研究发现，熊的心肌质量减少且心室僵硬度增加，而地松鼠在冬眠期间心肌质量增加且心室僵硬度降低。心肌可塑性的分子途径显示，在冬眠期间，两种动物在肌节蛋白（如肌联蛋白和α肌球蛋白重链）的修饰方面存在差异。冬眠特征的差异可能解释了这两种动物所表现出的不同心脏表型和功能策略。分子研究以及对季节性生理变化的更深入了解正在极大地推进我们对小型和大型冬眠动物及其进化差异的认识。
