Effects of Intermittent Hypoxia Adaptation on Experimental Heatstroke Rat Model

間歇性低氧適應對於熱中風保護機制之探討

熱中風為一種在世界各地都會發生之臨床急症，其臨床症狀有體溫過高，並且50﹪以上的遇難者伴有中樞神經系統損傷以及多重器官衰竭。在動物模式下發現，熱中風動物出現動脈血壓下降及顱內壓上升、腦缺血及腦神經細胞損傷，而腦內組織也釋放出大量的多巴胺(dopamine)、血清張力素(serotonin)、致熱性細胞介質素(cytokines)及麩胺酸(glutamate)。上述的熱中風症狀都能因事先於大鼠腦中誘發熱休克蛋白72 (HSP72)而減緩。於是我們假設大鼠經過數週間歇低氧訓練之後，可能會經由誘發體內重要器官（如腦組織、心臟、主動脈、腎上腺等）熱休克蛋白72型之表現，而改善在熱中風過程中之腦心血管功能，進一步對熱中風所致的循環性休克及腦缺血性神經細胞損傷產生保護作用。將SD雄鼠隨機分為間歇性低氧適應訓練組及對照組，間歇性低氧適應訓練組動物在低壓艙（壓力設定0.45 ATA）每天4小時，每星期訓練五天，如此持續訓練兩週。熱中風之誘發乃將大鼠持續曝露於高溫43 ℃下，當平均動脈壓與局部腦血流量自其高點迅速下降之時，視為熱中風生成。我們將比較有無運動訓練之大鼠在熱中風生成後，其血壓、心跳、腦血流及腦神經細胞損傷指數之差異。並測量在熱中風生成過程中，心血管動力參數的變化。另外在大鼠腦中植入顱內微透析探針來收集並偵測腦中一氧化氮之濃度與神經細胞損傷及缺血標記含量之變化，包括麩胺酸、甘油、乳酸、焦葡萄酸塩、一氧化氮及氧化自由基。腦皮質組織中之HSP72表現含量之分析則使用HSP72單株抗體，利用聚丙烯胺膠體電泳與西方墨漬技術偵測。結果顯示間歇性低氧適應訓練可以經由增加熱休克蛋白質72的表現並改善熱中風所引起之神經細胞損傷。

Heatstroke is a serious clinical problem in many parts of world. The symptoms of heatstroke include hyperthermia, central nervous system disorders and multiple organ failures in more than 50 % of the victims. In the animal model heatstroke, rats display arterial hypotension, intracranial hypertension, cerebral ischemia, cerebral dopamine, serotonin, cytokines and glutamate overload and cerebral neuronal damage. However, the above-mentioned heatstroke syndromes are attenuated by induction of heat shock protein 72 (HSP72) in rat brain. Other evidences have also demonstrated that HSP 72 can be detected in heart from rats with endurance exercise or hypoxia training. This raises the possibility that pretreatment of rats with physical exercise protects against the heatstroke-induced arterial hypotension, cerebral ischemia and cerebral neuronal damage via inducing HSP 72 and improves cardiovascular function of rats during heatstroke. Male SD rats are randomly assigned to either a heatstroke control group or to an intermittent hypoxia adaptation group. Trained animals were put in a hypoxia chamber 5 days/week, 4 hours/day with intensity 0.45 ATA for 2 weeks. Heatstroke is induced by exposing theanimals to a high temperature (43℃); the moment at which mean arterial pressure (MAP) and cerebral blood flow (CBF) decreased from their peak values is taken as the time of heatstroke onset. To address the question properly, we will compare the temporal profiles of MAP, CBF, heart rate and cerebral neuronal damage score after heatstroke in rats with or without physical exercise training and detect the changes of cardiovascular parameters (cardiac output and heart stroke volume) through the heatstroke period. Implanting an intracranial microdialysis probe will help assess the NO, free radicals release and markers of cerebral ischemia and cellular injury (including glycerol, glutamate and lactate/pyruvate ratio) in brain. The HSP 72 in brain cortex tissue was analyzed by SDS-PAGE and Western blotting with monoclonal anti-HSP 72 antibody. The data indicate that intermittent hypoxia adaptation increased HSP72 expression and attenuated heatstroke induced neuronal damage.