Bissonnette B, Pellerin L, Ravussin P, Daven V B, Magistretti P J
Department of Anaesthesia, University of Toronto, Ontario, Canada.
Anesthesiology. 1999 Dec;91(6):1763-9. doi: 10.1097/00000542-199912000-00030.
Deep hypothermia has been associated with an increased incidence of postoperative neurologic dysfunction after cardiac surgery in children. Recent studies suggest an excitotoxic mechanism involving overstimulation of glutamate receptors. Extracellular glutamate uptake occurs primarily by astrocytes. Astrocytes also store glycogen, which may be used to sustain the energy-consuming glutamate uptake. Extracellular glutamate and glycogen content were studied during temperature changes mimicking cardiopulmonary bypass in vivo.
Primary cultures of cerebral cortical astrocytes were used in a specially designed incubator allowing continuous changes of temperature and ambient gas concentrations. The sequence of events was as follows: normothermia, rapid cooling (2.8 degrees C/min) followed by 60 min of deep hypothermia (15 degrees C), followed by rewarming (3.0 degrees C/min) and subsequent 5 h of mild hyperthermia (38.5 degrees C). Two different conditions of oxygenation were studied: (1) normoxia (25% O2, 70% N2, 5% CO2); or (2) hyperoxia (95% O2, 5% CO2). The extracellular glutamate concentrations and intracellular glycogen levels were measured at nine time points.
One hundred sixty-two cultures were studied in four independent experiments. The extracellular concentration of glutamate in the normoxic group increased significantly from 35+/-10 nM/mg protein at baseline up to 100+/-15 nM/mg protein at the end of 5 h of mild hyperthermia (P < 0.05). In contrast, extracellular glutamate levels did not vary from control in the hyperoxic group. Glycogen levels decreased significantly from 260+/-85 nM/mg protein at baseline to < 25+/-5 nM/mg protein at the end of 5 h in the normoxic group (P < 0.05) but returned to control levels after rewarming in the hyperoxic group. No morphologic changes were observed in either group.
The extracellular concentration of glutamate increases, whereas the intracellular glycogen content decreases when astrocytes are exposed to a sequence of deep hypothermia and rewarming. This effect of hypothermia is prevented when astrocytes are exposed to hyperoxic conditions.
深度低温与儿童心脏手术后术后神经功能障碍发生率增加有关。最近的研究提示一种涉及谷氨酸受体过度刺激的兴奋性毒性机制。细胞外谷氨酸摄取主要由星形胶质细胞进行。星形胶质细胞还储存糖原，可用于维持消耗能量的谷氨酸摄取。在模拟体内心肺转流的温度变化过程中研究了细胞外谷氨酸和糖原含量。
在一个特别设计的培养箱中使用大脑皮质星形胶质细胞原代培养物，该培养箱允许温度和环境气体浓度持续变化。事件顺序如下：正常体温、快速降温（2.8℃/分钟），随后60分钟深度低温（15℃），接着复温（3.0℃/分钟）以及随后5小时轻度高温（38.5℃）。研究了两种不同的氧合条件：（1）常氧（25% O₂，70% N₂，5% CO₂）；或（2）高氧（95% O₂，5% CO₂）。在九个时间点测量细胞外谷氨酸浓度和细胞内糖原水平。
在四项独立实验中研究了162个培养物。常氧组细胞外谷氨酸浓度从基线时的35±10 nM/毫克蛋白显著增加至轻度高温5小时结束时的100±15 nM/毫克蛋白（P<0.05）。相比之下，高氧组细胞外谷氨酸水平与对照组无差异。常氧组糖原水平从基线时的260±85 nM/毫克蛋白显著降至5小时结束时的<25±5 nM/毫克蛋白（P<0.05），但高氧组复温后恢复至对照水平。两组均未观察到形态学变化。
当星形胶质细胞暴露于深度低温和复温序列时，细胞外谷氨酸浓度增加，而细胞内糖原含量减少。当星形胶质细胞暴露于高氧条件时，低温的这种效应可被预防。
