Estrogen and Ischemic Brain Injury Activation of Estrogen Receptor- and of Angiotensin-Converting Enzyme 2 Suppresses Ischemic Brain Damage in Oophorectomized Rats

Like the angiotensin II type 1 receptor blocker, endogenous estrogen (17 -estradiol) is neuroprotective against cerebral ischemia; its effects are thought to be mediated by estrogen receptors (ERs). To verify the role of ERs and the brain renin-angiotensin system in estrogen-deficient rats with ischemia induced by middle cerebral artery occlusion, we compared rats subjected to oophorectomy (OVX ) with sham-oophorectomized rats (OVX ) and OVX rats treated with 0.3 or 3.0 mg/kg of olmesartan for 2 weeks before middle cerebral artery occlusion. Independent of the blood pressure, the cortical infarct volume was larger in OVX than in OVX rats. It was smaller in olmesartan-pretreated OVX rats. The expression of ER in the peri-infarct region was correlated with the reduction of cortical infarct but not that of ER or G protein–coupled estrogen receptor. Olmesartan prevented ER downregulation in the cortical peri-infarct area, without affecting ER or G protein–coupled estrogen receptor. Olmesartan also increased mRNA expression of angiotensin-converting enzyme 2, Bcl-2, and Bcl-xL and reduced angiotensin II and cleaved caspase 3. These effects were augmented by olmesartan and abolished by the ER inhibitor. In OVX rats treated with the ER agonist alone, the infarct size was decreased, and the neuroprotective genes were upregulated. These findings suggest that the transactivation of neuroprotective genes and the reduction in brain angiotensin II are ER dependent and that this may augment neuroprotection together with an angiotensin II type 1 receptor blockade by olmesartan. We present the new insight that the activation of ER independent of estrogen contributes at least partly to limiting cerebral ischemic damage. (Hypertension. 2011;57:1161-1166.) ● Online Data Supplement