Churchill T A, Fedorow C A, Kneteman N M
Surgical-Medical Research Institute, University of Alberta, 1074 Dentistry-Pharmacy Building, Edmonton, Alberta, T6G 2N8, Canada.
Cryobiology. 1998 Mar;36(2):97-107. doi: 10.1006/cryo.1997.2065.
This study was designed to determine whether the metabolic adaptations developed by frogs to tolerate natural events of hypothermic hypoxia would precondition its liver for ex vivo organ storage. The metabolic responses of the frog, Rana castabiena, were compared to those of a mammalian system (rat) throughout a prolonged period of organ storage. Livers from rats and frogs were flushed and stored in UW solution at 5 degrees C for periods of 24-96 h. In frog livers, ATP was maintained high and constant over the first 24 h of storage; values ranged from 2.7 to 3.0 micro mol/g. Even after 96 h cold storage, ATP remained > 1.0 micro mol/g. In contrast, ATP levels in stored rat livers dropped rapidly, and by 4 h ATP was 1.2 micro mol/g. In terms of anaerobic endproduct accumulation, lactate levels rose 5.8 micro mol/g in frog liver (over 96 h) and by 8.6 micro mol/g in rat liver (over 24 h). This difference in flux through glycolysis was also reflected in relative rates of carbohydrate catabolism (i.e., glucose + lactate production). The rate of carbohydrate catabolism for frog liver was 0.74 micro mol/g/h compared to 2.26 micro mol/g/h for rat liver; a Q10 value of 6.2 was estimated for livers from R. castabiena. An assessment of glycolytic enzyme activities revealed that key differences in the responsiveness of pyruvate kinase to allosteric modifiers may have been responsible for the marked drop in the rate of anaerobic energy production in frog tissues. Although the concept of depressed metabolism in a lower vertebrate is not new, the data presented in this study demonstrate that a depressed metabolic state can be achieved in isolated livers from R. castabiena simply through cold exposure. With respect to clinical relevance, the results of this study indicate that energetics of stored livers can be maintained effectively through an efficient reduction in energy use in combination with a slow, yet continuous, rate of energy production facilitated by glycolysis.
本研究旨在确定青蛙为耐受自然低温缺氧事件而产生的代谢适应性是否会使其肝脏对离体器官保存产生预处理作用。在长时间的器官保存过程中，将卡斯蒂利亚蛙（Rana castabiena）的代谢反应与哺乳动物系统（大鼠）的代谢反应进行了比较。将大鼠和青蛙的肝脏冲洗后，置于4℃的UW溶液中保存24 - 96小时。在青蛙肝脏中，储存的前24小时内ATP保持在较高且恒定的水平；值范围为2.7至3.0微摩尔/克。即使经过96小时的冷藏，ATP仍保持>1.0微摩尔/克。相比之下，储存的大鼠肝脏中的ATP水平迅速下降，到4小时时ATP为1.2微摩尔/克。就厌氧终产物积累而言，青蛙肝脏中的乳酸水平在96小时内上升了5.8微摩尔/克，而大鼠肝脏在24小时内上升了8.6微摩尔/克。糖酵解通量的这种差异也反映在碳水化合物分解代谢的相对速率上（即葡萄糖+乳酸产生）。青蛙肝脏的碳水化合物分解代谢速率为0.74微摩尔/克/小时，而大鼠肝脏为2.26微摩尔/克/小时；估计卡斯蒂利亚蛙肝脏的Q10值为6.2。对糖酵解酶活性的评估表明，丙酮酸激酶对变构调节剂反应性的关键差异可能是青蛙组织中厌氧能量产生速率显著下降的原因。虽然低等脊椎动物代谢受抑制的概念并不新鲜，但本研究提供的数据表明，仅通过冷暴露就能使卡斯蒂利亚蛙的离体肝脏达到代谢受抑制状态。就临床相关性而言，本研究结果表明，通过有效减少能量使用以及糖酵解促进的缓慢但持续的能量产生速率，可以有效地维持储存肝脏的能量学。
