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The enhanced protective effect of postconditioning by 17β‐estradiol after transient focal cerebral ischemia in mice

The aim of this study was to explore the enhancement of 17β‐estradiol (E2) in the neuroprotective effect of ischemic postconditioning (PostC) following transient focal cerebral ischemia in mice. Adult female mice were ovariectomied two weeks before 30 min transient focal cerebral ischemia induced by right middle cerebral artery occlusion. E2 or vehicle (sesame oil) was administered following the reperfusion immediately. PostC consisted of 3 cycles of 15 s reperfusion/15 s occlusion on right common carotid artery. Brains were obtained 24 h, 2 d, 3 d and 5 d after permanent reperfusion. Nissl staining was used to measure the infarct sizes and neurological scores were evaluated. Levels of TNF‐α, IL‐1β and IL‐6, and expressions of caspase 3 and Bcl‐2 in brain homogenates were analyzed. We found that E2 enhanced the infarct‐limiting effect and improvement of neurological score by PostC. Levels of TNF‐α, IL‐1β and IL‐6 in brain homogenates from E2 treated postconditioned mice were significantly lower than those in vehicle treated group. Expression of caspase 3 and Bcl‐2 in brains of postconditioned mice with E2 treatment showed lower levels than that of vehicle treated group. These results provide first evidence that E2 enhances the neuroprotective effect of ischemic PostC at least via antagonizing inflammation and apoptosis induced by cerebral ischemia and reperfusion.