亚低温对创伤性脑损伤后线粒体呼吸功能和超微结构的影响

Changes of cerebral mitochondrial respiratory function and ultrastructure after traumatic brain injury in response to hypothermia

目的研究亚低温治疗对创伤性脑损伤（TBI）大鼠线粒体超微结构和呼吸功能的影响。方法利用液压打击（FPI）制作中度TBI大鼠模型，并随机分为假手术对照组、常温TBI组（肛温36～37℃）、亚低温TBI组（肛温31～33℃，低温持续2h）。各组于脑外伤后2，24h、3d和7d断头取脑，取伤侧海马组织固定，透射电镜观察线粒体形态改变。差速离心法提取伤侧大脑线粒体，采用Clark氧电极法测定线粒体的氧呼吸速率，计算呼吸控制比（RCR）值和磷氧比值（P／O）。结果（1）电镜下常温TBI组线粒体结构形态损伤程度较重，亚低温TBI组线粒体形态基本完好；（2）线粒体RCR值和P／O值在TBI后2h就显著下降，以24h为最低（P〈0．01），在7d时RCR仍然显著低于假手术对照组，P／O值恢复正常。亚低温TBI组线粒体RCR值变化趋势同常温TBI组，但在3d内RCR值均显著高于常温TBI组，P／O值在3d后恢复正常。结论TBI后，线粒体的呼吸功能明显下降，亚低温可以明显改善线粒体的呼吸功能，保护线粒体结构完整性。

Objective To study the effect of hypothermia on cerebral mitochondrial respiratory function and ultrastructure after traumatic brain injury （TBI）. Methods Spragne-Dawley rats were subjected to moderate brain injury by using lateral fluid-percussion （LFP） and randomly divided into sham operation group, normothermic TBI group （rectal temperature for 36-37℃ ） and hypothermic TBI group （rectal temperature for 31-32℃ lasting for two hours）. The ipsilateral brains were dissected and homogenized brain tissues were extracted to obtain mitochondria by density-centrifugation and speed-centrifugation at 2, 24 hours and at days 3 and 7 after TBI. The mitochondrial ultrastructure was studied by electron microscope. The indices of respiratory control rate （RCR） and P/O ratio of mitochondrial respiratory function were measured after oxygen consumption was determined with a Clark-type electrode. Results The mitochondrial ultrastructure of normothermic TBI group was damaged severely while that of hypothermic TBI group kept relatively integrated. The RCR and P/O ratio were markedly decreased two hours after TBI and reached the lowest level at the 24th hour （P 〈 0.01 ）. At day 7, RCR kept at a lower level compared with sham operation group but P/O ratio recovered to normal. Change of RCR was similar in hypethermic TBI group and normothermic TBI group. However, RCR of the hypethermic TBI group was significantly higher than that of the normothermic TBI group within three days after TBI. In the meantime, P/O ratio recovered to normal three days after TBI. Conclusion Hypothermia can improve cerebral mitochondrial respiratory function and protect the mitochondrial structure after TBI.