BACKGROUND: Hypoxia inducible factor-1 alpha (HIF-1 α) and erythropoietin(EPO), possessing neuroprotective effect in the cerebral ischemia, might play an important role in the formation of cerebral ischemic tolerance (IT).OBJECTIVE:To observe the neuroprotective effect of cerebral ischemic preconditioning(IPC) of rats, and the expression and mechanism of HIF-1α and target gene erythropoietin in the brain tissue following the formation of cerebral IT.DESIGN :A randomized and controlled observation.SETTING: Department of Neurology, the Affiliated Hospital of Medical College, Qingdao University.MATERIALS: Totally 84 enrolled adult healthy male Wistar rats of clean grade, weighing 250 to 300 g, were provided by the Animal Experimental Department, Tongji Medical College of Huazhong University of Science and Technology. Ready-to-use SABC reagent kit and rabbit anti-rat HIF-1α monoclonal antibody were purchased from Boshide Bioengineering Co. Ltd (Wuhan); Rabbit anti-rat EPO monoclonal antibody was purchased from Santa Cruz Company (USA).METHODS: This experiment was carried out in the Department of Anatomy, Medical College, Qingdao University during March 2005 to March 2006. ① The 84 rats were divided into 3 groups by a lot: IPC group (n=40),sham-operation group (n=40) and control group (n=4). In the IPC group, middle cerebral artery was occluded for 2 hours respectively on the 1st, 3rd, 7th, 14th and 21st days of the reperfusion following 10-minute preischemia was made using a modified middle cerebral artery second suture method from Zea-Longa. The rats were sacrificed 22 hours after reperfusion in the end of middle cerebral artery occlusion (MCAO). That was to say,after 10-minute preischemia, suture was exited to the extal carotid artery and embedded subcutaneously.Middle cerebral artery was occluded again to form the second reperfusion at the set time point after reperfusion. Twenty-two hours later, rats were sacrificed; In the sham-operation group,the preischemia was substituted by sham-operation(only common carotid artery and crotch were exposed, and MCAO by suture was omitted), and the other procedures were the same as those in the IPC group. In the control group, rats were given sham-operation twice at an interval of one day, and they were sacrificed 24 hours after the second sham-operation. ② Brain tissue was taken from the rats in each group. Cerebral infarction area of each layer was measured with TTC staining, and total cerebral infarction volume (The total cerebral infarction area of each layer×interspace ) was calculated. After brain tissue was stained by haematoxylin-esoin (HE), the form of nerve cells was observed under an optical microscope, and the expressions of HIF-1αand EPO protein in the brain tissue were detected with immunohistochemical method.MAIN OUTCOM E MEASURES: ①Cerebral infarction volume;②form of nerve cell; ③ the expression of HIF-1αand EPO protein in the brain tissue.RESULTS:Totally 84 rats were enrolled in the experiment. The dead rats were randomly supplied during the experiment, and finally 84 rats entered the stage of result analysis. ① Detection of cerebral infarction volume of rats in each group: Cerebral infarction volume in the IPC group was significantly smaller than that in the sham-operation group on the 1st, 3rd and 7th days after reperfusion respectively [(161.2±6.9) mm3 vs (219.9±11.2) mm3, (134.9±9.0) mm3 vs (218.6±13.0) mm3, (142.9±13.7) mm3 vs (221.3±14.2) mm3, t=-8.924,10.587,7.947, P＜ 0.01]. ② Observation of nerve cell form of brain tissue: HE staining showed that the ischemic degree, range and cerebral edema degree of IPC group were significantly milder than those of sham-operation group. ③ The expressions of HIF-1α and EPO protein in cerebral cortex and hippocampus:The expression of HIF-1αof IPC group was significantly higher than that of sham-operation group on the 1st,3rd and 7th days after reperfusion respectively (125.93±3.79 vs 117.65±5.60, 140.63±4.64 vs 119.33±4.26,131.15±2.74 vs 107.60±3.89, t=-2.449, 6.763,9.899,P＜ 0.05-0.01). The expression of EPO of IPC group was significantly higher than that of sham-operation group on the 3rd and 7th days after perfusion respectively (141.68±3.29 vs 126.33±4.51, 138.88±2.59 vs 125.58±6.18, t=5.499,3.970, P ＜ 0.05).CONCLUSION: ① IPC can protect the never cells in rat brain and the best time to onset of cerebral IT induced by IPC is 1 to 7 days after reperfusion. ② Neuroprotective effect of cerebral IT might be related to the expression of HIF-1α and its target gene EPO.