BACKGROUND:Estrogen has been clinically demonstrated to attenuate ischemic brain injury.However,the precise mechanisms remain controversial.OBJECTIVE:To investigate the effects of estradiol on angiopoietin-1 mRNA and Bcl-2 expression,as well as apoptosis and cerebral blood flow,in ovariectomized rats with focal cerebral ischemia following reperfusion.DESIGN,TIME AND SETTING:Randomized,controlled,animal experiment.The study was performed at the Central Laboratory,Chongqing Medical University from September to December 2005.MATERIALS:Estradiot benzoate was purchased from Shanghai Ninth Pharmaceutical Factory;c oil was purchased from Walmart Supercenter;TUNEL kit,rabbit anti-rat Bcl-2 polyclonal antibody,and biotin-labeled goat anti-rabbit antibody were purchased from Wuhan Boster,China.METHODS:Healthy,female,6-month-old Wistar rats-wild-type and estrogen alpha receptor gene knockout (ERKO)-were randomly divided into estradiol and control groups with 25 animals in each group.The rats were intramuscularly injected with estradiol benzoate (100 μg/kg per day) at 30 days following bilateral ovariectomy or c oil (1 mL/kg per day) for seven consecutive days.Following administration,cerebral ischemia/reperfusion models were established using the right middle cerebral artery occlusion (MCAO) method.After 30 minutes of MCAO,estradiol and control groups were separately injected with estradiol benzoate and c oil with the above-mentioned doses.MAIN OUTCOME MEASURES:Cell apoptosis was determined by TUNEL;angiopoietin-1 mRNAand Bcl-2 gene expression was determined,respectively,by immunohistochemical staining and RT-PCR.In addition,changes in cerebral blood flow were measured by laser Doppler flowmetry.RESULTS:Changes in angiopoietin-1 mRNA and cerebral blood flow in estradiol-treated,wild-type,MCAO rats following ischemia/reperfusion were greater than in control rats (P＜0.01 or 0.05).However,no significant difference was observed between estradiol-treated ERKO MCAO rats and control rats.In addition,estradiol-treated wild-type and ERKO MCAO rats exhibited significantly increased Bcl-2 expression (P＜0.05) and decreased number of apoptotJc cells Jn brain tissues compared with control groups (P＜0.05).CONCLUSION:Estradiol upregulated angiopoietin-1 mRNA and Bcl-2 expression,suggesting that estradiol might be involved in protective mechanisms of cerebral ischemia/reperfusion injury.