Abstract: Objective To investigate the expression of vascular endothelial growth factor(VEGF) and changeof microvascular density(MVD) in the rat model of brain ischemic tolerance induced by ischemiapreconditioning.Methods Ninety-Nine Wistar rats were randomly assigned to three groups: sham surgery(n =9),non-ischemic preconditioning (NIP, n =45), and ischemic preconditioning(IP, n =45). The NIP groupand IP group were equally divided into five subgroups according to time of ischemia-reperfusion,including 1, 3, 7, 14 and 21 days subgroups. For IP, the rats were given middle cerebral arteryocclusion(MCAO) for 10 minutes. At 1, 3, 7, 14 and 21 days after IP, the rats were given the secondMCAO for 2 h followed by 22 h reperfusion. In the NIP group, pre-ischemia was replaced by shamsurgery. The sham surgery group received the sham surgery twice. Brain sections were stainedwith 2.3.5-triphenyl tetrazolium ch(TTC) for surveying the volume of infraction. The expressionof microvascular density was determined by immunohistochemical staining and the expression ofVEGF mRNA was determined by in situ hybridization.Results ①Intergroup comparison:Both the infarct volume and the expression of VEGF mRNAof animals in the sham surgery group were zero. compared with the NIP group, infarct volumesignificantly decreased in the 1, 3, 7 days subgroups of IP group(P <0.001). The expressionof VEGF mRNA significantly increased in the ischemic hemisphere at 1, 3, 7 days subgroupsof IP group(P :0.002, 0.001, 0.001). The expression of MVD significantly increased at 3, 7 dayssubgroups(P :0.012, 0.001). ②In the IP group, infarct volume significantly decreased in the 3days subgroups(P <0.05). The expression of MVD at 7 days, VEGF mRNA at 3 days significantlyincreased compared with other groups(P <0.05). ③There was a positive correlation betweenexpression of VEGF mRNA and change of MVD, but was not obviously(r =0.472, P =0.017).Conclusion Ischemic preconditioning upregulated the expression of VEGF mRNA and MVD, andthey may play important roles in the process of brain ischemic tolerance.

Key words: Brain ischemia; Vascular endothelial growth factors; Angiogenesis; Rats

摘要： 目的 观察局灶性缺血预处理诱导脑缺血耐受大鼠血管内皮生长因子（vascular endothelial growth factor，VEGF）的表达及微血管密度（MVD）的变化。方法 将99只Wistar大鼠随机分成对照组9只、非缺血预处理（non-ischemic preconditioning，NIP）组45只、缺血预处理（ischemic preconditioning，IP）组45只，后两组按照再灌注时间随机分成1 d，3 d，7 d，14 d，21 d，5个亚组，每亚组9只大鼠。对IP组采用线栓法阻塞大鼠大脑中动脉建立局灶性IP模型，分别在IP后1 d，3 d，7 d，14 d，21 d对大鼠进行再次缺血2 h再灌注22 h，然后取脑检查。测定脑梗死体积，免疫组化检测MVD变化，原位杂交法检测VEGF信使核糖核酸（messenger RNA，mRNA）表达。结果 ①组间比较：对照组无梗死灶，未见有VEGF mRNA表达，IP组1 d，3 d，7 d亚组梗死体积较NIP组相应亚组明显减小（P均为0.001）。IP组1 d，3 d，7 d亚组VEGF mRNA较NIP组相应亚组表达明显增高（P分别为0.002、0.001、0.001），IP组3 d，7 d亚组MVD较NIP组相应亚组表达明显增高（P分别为0.012、0.001）。②组内比较：IP组3 d亚组梗死体积减小最为明显，明显小于同组内其他亚组（与1 d、7 d、14 d、21 d亚组相比，P分别为0.001、0.042、0.001、0.001）；7 d亚组微血管在缺血灶周边区分布最为密集，MVD明显高于同组内其他亚组（与1 d、3 d、14 d、21 d亚组相比，P分别为0.001、0.003、0.004、0.001）；VEGF mRNA在IP后1 d表达即开始升高，高峰出现在IP后3 d，持续至7 d，且IP组3 d亚组VEGFmRNA表达明显高于同组内其他亚组（与1 d、7 d、14 d、21 d亚组相比，P分别为0.001、0.038、0.007、0.005）。③VEGF mRNA表达与MVD变化呈一定正相关性（r =0.472，P =0.017）。结论 VEGF mRNA及MVD在缺血预处理诱导大鼠脑缺血耐受的相应时间点内表达有所增加，VEGF及微血管形成可能在脑缺血耐受中发挥了重要作用。

关键词: 脑缺血; 血管内皮生长因子类; 血管形成; 大鼠