中低温体外循环对大鼠海马CA1区神经元凋亡的影响

Effects of mild hypothermic cardiopulmonary bypass on neuronal apoptosis in hippocampus CA1 region in rats

目的 观察中低温体外循环(CPB)对大鼠海马CA1区神经元凋亡的影响及机制。方法 雄性SD大鼠27只,随机分为三组:CPB后1h组(n=6)、CPB后6h组(n=6)及假手术组(Sham组,n=5)。所有动物在咪唑安定、芬太尼麻醉后经口插管控制呼吸,置入颈静脉流出管和尾动脉输入管,肝素抗凝(500μ/kg)。CPB组采用中低温CPB(26～28℃),经尾动脉灌注、颈静脉右心房-腔静脉引流,灌流量160ml·kg^(-1)·min^(-1),总转流时间2h,Sham组操作同CPB术后1h组,但不经历CPB,三组持续监测动脉压、ECG及动脉血气。CPB后1h组、CPB后6h组分别在术后1、6h时处死大鼠,4％多聚甲醛灌注固定后取大脑组织,TUNEL法检测神经元凋亡,并用电子显微镜观察神经元超微结构变化,用免疫组化法检测海马CA1区神经元bax和bcl-2蛋白表达。结果 与Sham组比较,CPB后1h组bax和bcl-2蛋白表达增强,CPB后6h组bax表达增强、bcl-2蛋白表达减弱(P<0.05);与CPB后1h组比较,CPB后6h组bax表达增强、bcl-2蛋白表达减弱(P<0.05)。与Sham组比较,CPB后1h、CPB后6h组bax/bcl-2比值、神经元凋亡率升高,CPB后6h组bax/bcl-2比值、神经元凋亡率高于CPB后1h组(P<0.05)。电镜下CPB后1h组海马CA1区神经元部分线粒体肿胀、空泡变性、嵴减少或消失;CPB后6h组可见少量神经元变性固缩、核不规则。

Objective To investigate the effects of mild hypothermic cardiopulmonary bypass(CPB) on bax and bcl-2 protein expression and neuronal apoptosis in hippooampus CA1 region in rats. Methods Healthy male SD rats weighing 380-420g were randomly divided into 3 groups: (1)post-CPB 1h group (n=6); (2) post-CPB 6h group (n=6) and (3) sham CPB group(n=5). The animals were anesthetized with intraperitoneal fentanyl 150μg·kg^(-1), midazolam 1 mg·kg^(-1) and vecurunium 0.1 mg·kg^(-1), intubated and mechanically ventilated. Left femoral artery was cannulated for heparinizafion, BP monitoring and blood sampling. Artery in the tail and right jugular vein were cannulated for CPB. The animals in group 1 and 2 underwent 2 h mild hypothermic (26-28℃) CPB at a flow of 160 ml·kg^(-1)·min^(-1). 1h(group 1) and 6h(group 2) after CPB 4% polymerized formaldehyde was injected via the artery in the tail. Brains were immediately removed. Bax and bcl-2 protein expression in hippocampus CA1 region was determined by immuno-histochemistry method and neuronal apoptosis by TUNEL technique. Ultrastructural changes were examined with electron microscope. Results (1)Bax and Bcl-2 protein expressions were significantly higher in group 1(1h after CPB)than in sham CPB group. Bax protein expression was significantly higher but bcl-2 protein expression was significantly lower in group 2 than in group 1. bax/bcl-2 ratio in group 2(at 6h after CPB)was significantly higher than that in group 1(at 1h after CPB). (2) Neuronal apoptosis was significantly increased in group 1 and 2 compared to sham CPB group. (3) Electron microscopy showed that some mitochondria were moderately or severely swollen with vacuolizafion and decreased number of mitochondrial at 1h after CPB and at 6h after CPB there was shrinkage of neuronal cells with irregular shape of nucleus, notches in nuclear membrane and margination of nucleoli. Conclusion CPB induces upregulation of both bax and bcl-2 protein expression with predominance of the pro-apoptotic gene Bax leading to increased neuronal apoptosis, indicating that CPB can cause brain injury.