褪黑素对异氟醚麻醉诱发老龄大鼠认知功能障碍的影响

Effect of melatonin on isoflurane anesthesia-induced cognitive dysfunction in aged rats

目的探讨褪黑素对异氟醚麻醉诱发老龄大鼠认知功能障碍的影响。方法雄性SD大鼠75只，18～20月龄，体重350～400g，采用随机数字表法，将其随机分为5组（n=15）：对照组（c组）吸入含有30％氧气的空氧混合气体4h；异氟醚麻醉组（Ⅰ组）吸入1．5％异氟醚4h；褪黑素5mg／kg组（M1组）、褪黑素10mg／kg组（M2组）、褪黑素20mg／kg组（M，组）分别于麻醉前15min和麻醉开始后3h时腹腔注射褪黑素5、10、20mg／kg（溶解于含1％DMSO的生理盐水中），吸入1．5％异氟醚gh。麻醉结束即刻每组取5只大鼠，进行动脉血气分析，测定血糖水平和海马磷酸化Tau（p-Tau）蛋白的表达。麻醉结束后ldd时，每组取10只大鼠测定认知功能，然后处死大鼠，取海马组织，采用Western blot法检测p-Tau蛋白的表达。结果五组间动脉血气指标和血糖水平差异无统计学意义（P〉0．05）。与c组比较，I组和M1组第3～5天时逃避潜伏期延长，探索时间缩短，海马p-Tau蛋白表达上调（P〈0．05），M2组和M3组逃避潜伏期、探索时间和海马p-Tau蛋白表达差异无统计学意义（P〉0．05）；与I组和M1组比较，M2组和M3组第2～5天时逃避潜伏期缩短，探索时间延长，海马p—Tau蛋白表达下调（P〈0．05）；I组与M1组间、M2组与M3组间逃避潜伏期、探索时间和海马p-Tau蛋白表达比较差异无统计学意义（P〉0．05）。结论褪黑素（10和20mg／kg）可改善异氟醚麻醉诱发老年大鼠认知功能障碍，其机制可能与其抑制海马Tau蛋白过度磷酸化有关。

Objective To investigate the effect of melatonin on isoflurane anesthesia-induced cognitive dysfunction in aged rats. Methods Seventy-five male SD rats, aged 18-20 months, weighing 350-400 g, were randomly assigned into 5 groups （ n = 15 each） ： control group （group C）, 1.5% isoflurane group （group I）, melatonin 5 mg/kg group （ group M1 ）, melatonin 10 mg/kg group （ group M2 ） and melatonin 20 mg/kg group （ group M3 ）. Group C inhaled a gas mixture of oxygen and air for 4 h and group I inhaled 1.5 % isoflurane for 4 h. Melatonin 5, 10 and 20 mg/kg （in normal saline containing 1% DMSO） were injected intraperitoneally at 15 min before anesthesia and 3 h after the beginning of anesthesia in groups M, , M2 and M3 respectively, and then the animals inhaled 1.5 % isoflurane for 4- h. At the end of anesthesia, 5 rats in each group were chosen and blood sam- pies were taken to perform arterial blood gas analysis and to detect the blood glucose level and expression of phos- phorylated Tau （p-Tau） protein in hippocampus. Ten rats in each group were chosen at 14 d after the end of anes- thesia and Morris water maze was performed 3 times a day for 5 consecutive days to assess the cognitive function. Then the animals were sacrificed and hippocampi were removed for detection of p-Tau expression by Western blot. Results There were no significant differences in the parameters of arterial blood gas analysis and blood glucose level among the 5 groups （ P 〉 0.05）. Compared with group C, the escape latency at 3-5 d was significantly prolonged, the probe time was significantly shortened, and the expression of p-Tau protein was up-regulated in groups I and M1 （ P 〈 0.05）, and no significant change was found in the indexes mentioned above in groups M2 and M3 （ P 〉 0.05） . Compared with groups I and M1 , the escape latency at 2-5 d was significantly shortened, the probe time was significantly prolonged, and the expression of p-Tau protein was down-regulated in groups ME and M3 （ P 〈 0.05）. There were no significant differences in the indexes mentioned above between groups I and M1 , and between groups M2 and M3 （ P 〉 0.05）. Conclusion Melatonin （ 10 and 20 mg/kg） can improve isoflurane anesthesia-induced cognitive dysfunction in aged rats, which may be related to inhibition of hyperphosphorylation of Tau protein in hippocampus.