Estrogen-mediated neuroprotection after experimental stroke in male rats

Background and Purpose - We have previously shown that 17β-estradiol reduces infarction volume in female rats. The present study determined whether single injection or chronic implantation of estrogen confers neuroprotection in male animals with middle cerebral artery occlusion (MCAO) and whether there is an interaction with endogenous testosterone. Methods - Male Wistar rats were treated with 2 hours of reversible MCAO. In protocol 1, acute versus chronic estrogen administration was examined in groups receiving the following: Premarin (USP) 1 mg/kg IV, immediately before MCAO (Acute, n=13, plasma estradiol = 171±51 pg/mL); 7 days of 25 μg (E25, n=10, 10±3 pg/mL) or 100 μg 17β-estradiol (E100, n=12, 69±20 pg/mL) by subcutaneous implant; or saline (SAL, n=21, 3±1 pg/mL). Laser-Doppler flowmetry was used to monitor the ipsilateral parietal cortex throughout the ischemic period and early reperfusion. At 22 hours of reperfusion, infarction volume was determined by 0 2,3,5-triphenyltetrazolium chloride staining and image analysis. In protocol 2, rats were castrated to deplete endogenous testosterone and then treated with estradiol implants: castration only (CAST, n=13, estradiol = 5±2 pg/mL), sham-operated (SHAM, n=10, 4±2 pg/mL), estradiol implant 25 μg (CAST+E25, n=16, 7±2 pg/mL) or 100 μg (CAST+E100, n=14, 77±14 pg/mL). Results - Cortical infarct volumes were reduced in all estrogen-treated groups: Acute (21±4% of ipsilateral cortex), E25 (12±5%), and E100 (12±3%) relative to SAL (38±5%). Caudate infarction was similarly decreased: Acute (39±7% of ipsilateral striatum), E25 (25±7%), and E100 (34±6%) relative to SAL (63±4%). Castration did not alter ischemic outcome; cortical and caudate infarction (percentage of respective ipsilateral regions) were 37±5% and 59±5% in CAST and 39±7% and 57±5% in SHAM, respectively. Estrogen replacement reduced infarction volume in castrated animals in cortex (19±4% in CAST+E25 and 12±4% in CAST+E100) and in caudate (42±6% in CAST+25 and 20±7% in CAST+100). Laser-Doppler flowmetry results during ischemia and reperfusion was not different among groups. Conclusions - Both acute and chronic 17β-estradiol treatments protect male brain in experimental stroke. Testosterone availability does not alter estradiol- mediated tissue salvage after MCAO.