Selective Estrogen Receptor Modulator LY353381.HCl-Mediated Neuroprotection and BCL-2 Expression After Experimental Stroke
Estrogen replacement in ovariectomized rats reduces cerebral tissue infarction sustained after experimental stroke. We hypothesized that LY353381.HCl, a selective estrogen receptor modulator (SERM), reduces cerebral tissue infarction after middle cerebral artery occlusion (MCAO), and that the mechanism of protection is not related to preservation of blood flow. After 5–9 days of treatment with LY353381.HCl (LY) or vehicle (VEH), ovariectomized rats were subjected to 2 hours of MCAO under halothane anesthesia, followed by 22 hours of recovery. Ischemia was confirmed by laser-Doppler flowmetry. MAP, blood gases, and rectal and temporalis muscle temperature were controlled. Infarct volumes were measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining and digital image analysis. Ovariectomized (OVX) rats treated with LY (n=16) had smaller infarct volumes in the caudoputamen (CP) than VEH (n=14) treated rats, 49%±6% vs. 64%±4% of ipsilateral CP, respectively, P<0.05. Cerebral cortical (CTX) infarct size was not statistically different between treatment groups (7%±3% vs. 13%±4% for LY vs. VEH, respectively). In a second cohort of OVX rats, end ischemic regional cerebral blood flow (CBF) was measured by 14C-iodoantipyrine autoradiography in LY (n=4) and VEH (n=3) treated rats. Absolute ischemic CBF and tissue volume distribution to low flow zones were similar in both groups. In a final cohort, 22 hours post MCAO, tissue was sampled from representative regions of CTX and CP in OVX (n=5) and LY (n=4) treated groups and analyzed for BCL-2 mRNA expression using ribonuclease protection assay. LY increased BCL-2 mRNA in both ipsilateral CTX and CP. We conclude that LY353381.HCl confers protection from focal cerebral ischemia by mechanisms that are not related to CBF but may involve increased BCL-2 expression.