Donohoe P H, West T G, Boutilier R G
Department of Zoology, University of Cambridge, United Kingdom.
Am J Physiol. 1998 Mar;274(3):R704-10. doi: 10.1152/ajpregu.1998.274.3.R704.
Aerobic metabolic rates (MO2) and respiratory quotients (RQ = CO2 production/MO2) were measured contemporaneously in hibernating frogs Rana temporaria (L.), submerged for 90 days at 3 degrees C. After 3 mo of submergence in fully aerated water, MO2 levels were 61% of those seen at the same temperature before hibernation. Over the first 40 days of hibernation, RQ values (< or = 0.82) favored a lipid-based metabolism that progressively shifted to an exclusively carbohydrate metabolism (RQ = 1.01) by 90 days of hibernation. Liver glycogen concentrations fell by 68% during the first 8 wk of submergence, thereafter exhibiting a less rapid rate of utilization. Conversely, muscle glycogen concentrations remained stable over the first 2 mo of the experiment before falling by 33% over the course of the remaining 2 mo, indicating that the frog was recruiting muscle glycogen reserves to fuel metabolism. Submerged frogs exhibited an extracellular acidosis during the first week of submergence, but over the course of the next 15 wk "extracellular pH" values were not significantly different from the values obtained from the control air-breathing animals. The initial extracellular acidosis was not mirrored in the intracellular compartment, and the acid-base state was not significantly different from the control values for the first 8 wk. However, over the subsequent 8- to 16-wk period, the acid-base status shifted to a lower intracellular pH-HCO3 concentration set point, indicative of a metabolic acidosis. Even so, there was no indication that the acidosis could be attributed to anaerobic metabolism, as both plasma and muscle lactate levels remained low and stable. Muscle adenylate energy charge and lactate-to-pyruvate and creatine-to-phosphocreatine ratios also remained unchanged throughout hibernation. The capacity for profound metabolic rate suppression together with the ability to match substrate use to shifts in aerobic metabolic demands and the ability to fix new acid-base homeostatic set points are highly adaptive, both in terms of survival and reproductive success, to an animal that is often forced to overwinter under the cover of ice.
在3摄氏度的环境中，对处于冬眠状态的林蛙（Rana temporaria，L.）进行了为期90天的水下浸泡实验，同时测定了其有氧代谢率（MO2）和呼吸商（RQ = CO2产生量/MO2）。在完全曝气的水中浸泡3个月后，MO2水平仅为冬眠前相同温度下的61%。在冬眠的前40天里，RQ值（≤0.82）表明其代谢以脂质为主，到冬眠90天时逐渐转变为完全以碳水化合物为基础的代谢（RQ = 1.01）。肝脏糖原浓度在浸泡的前8周下降了68%，此后利用率下降速度减缓。相反，肌肉糖原浓度在实验的前2个月保持稳定，在随后的2个月中下降了33%，这表明青蛙正在动用肌肉糖原储备来为代谢提供能量。浸泡的青蛙在浸泡的第一周出现细胞外酸中毒，但在接下来的15周内，“细胞外pH值”与对照的空气呼吸动物的值没有显著差异。最初的细胞外酸中毒在细胞内没有体现，并且在最初的8周内酸碱状态与对照值没有显著差异。然而，在随后的8至16周期间，酸碱状态转变为较低的细胞内pH-HCO₃浓度设定点，表明存在代谢性酸中毒。即便如此，没有迹象表明酸中毒可归因于无氧代谢，因为血浆和肌肉乳酸水平均保持在低水平且稳定。整个冬眠过程中，肌肉腺苷酸能量电荷以及乳酸与丙酮酸、肌酸与磷酸肌酸的比率也保持不变。对于经常被迫在冰层覆盖下越冬的动物而言，其深度抑制代谢率的能力，以及将底物利用与有氧代谢需求变化相匹配的能力，还有设定新的酸碱稳态设定点的能力，无论是在生存还是繁殖成功方面都具有高度适应性。
