Pérez-Pinzón M A, Rice M E
Department of Physiology, NYU Medical Center, NY 10016, USA.
Brain Res. 1995 Dec 24;705(1-2):45-52. doi: 10.1016/0006-8993(95)01136-6.
We determined the ascorbic acid (ascorbate) and glutathione (GSH) contents of eight regions of the CNS from anoxia-tolerant turtles collected in summer and in winter. Ascorbate was of special interest because it is found in exceptionally high levels in the turtle CNS. The temperature-dependence of CNS ascorbate content was established by comparing levels in animals collected from two geographic zones with different average winter temperatures and in animals re-acclimated to different temperatures in the laboratory. The analytical method was liquid chromatography with electrochemical detection. Turtle ascorbate levels were 30-40% lower in animals acclimatized to winter (2 degrees C) than to summer (23 degrees C) in all regions of the CNS. Similarly, GSH levels were 20-30% lower in winter than in summer. Winter ascorbate levels were higher in turtles from Louisiana (19 degrees C) than in turtles acclimatized to winter in Wisconsin (2 degrees C). Summer and winter levels of ascorbate could be reversed by re-acclimating animals to cold (1 degree C) or warm (23 degrees C) temperatures for at least one week. CNS water content did not differ between cold- and warm-acclimated turtles. Taken together, the data indicated that ascorbate and GSH undergo significant seasonal variation and that the catalyst for change is environmental temperature. Steady-state ascorbate content showed a linear dependence on temperature, with a slope of 1.5% per degree C that was independent of CNS region. Lower levels of cerebral antioxidants in turtles exposed to colder temperatures were consistent with the decreased rate of cerebral metabolism that accompanies winter hibernation. Cerebral ascorbate and GSH levels in the turtle remained similar to or higher than those in mammals, even during winter, however. These findings support the notion that unique mechanisms of antioxidant regulation in the turtle contribute to their tolerance of the hypoxia-reoxygenation that characterizes diving behavior.
我们测定了夏季和冬季采集的耐缺氧海龟中枢神经系统八个区域的抗坏血酸（维生素C）和谷胱甘肽（GSH）含量。抗坏血酸特别受关注，因为在海龟中枢神经系统中发现其含量异常高。通过比较从两个平均冬季温度不同的地理区域采集的动物以及在实验室中重新适应不同温度的动物体内的含量，确定了中枢神经系统抗坏血酸含量的温度依赖性。分析方法为电化学检测液相色谱法。在中枢神经系统的所有区域，适应冬季（2摄氏度）的动物体内海龟抗坏血酸水平比适应夏季（23摄氏度）的动物低30 - 40%。同样，冬季GSH水平比夏季低20 - 30%。来自路易斯安那州（19摄氏度）的海龟冬季抗坏血酸水平高于在威斯康星州适应冬季（2摄氏度）的海龟。通过将动物重新适应寒冷（1摄氏度）或温暖（23摄氏度）温度至少一周，可使夏季和冬季的抗坏血酸水平逆转。适应寒冷和温暖环境的海龟中枢神经系统含水量没有差异。综合来看，数据表明抗坏血酸和GSH经历显著的季节性变化，且变化的催化剂是环境温度。稳态抗坏血酸含量显示出对温度的线性依赖性，每摄氏度斜率为1.5%，且与中枢神经系统区域无关。暴露于较低温度下的海龟大脑抗氧化剂水平较低，这与冬季冬眠时大脑代谢率降低一致。然而，即使在冬季，海龟大脑中的抗坏血酸和GSH水平仍与哺乳动物相似或更高。这些发现支持了这样一种观点，即海龟体内独特的抗氧化调节机制有助于它们耐受潜水行为所特有的缺氧 - 复氧过程。
