Estradiol: a protective factor in the adult brain.

Clinical studies suggest that estradiol acts as a protective factor in the adult brain. Postmenopausal women suffer from an increased risk of brain injury associated with neurodegenerative diseases such as Alzheimer's disease, and estrogen replacement therapy appears to decrease the risk and severity of this neurodegenerative condition. Studies using animal models show that estradiol exerts similar effects in rodents and can enhance cell survival. Therefore, we designed experiments to determine whether estradiol treatment can decrease brain injury induced by an experimental model of ischemia. Our experiments used a permanent middle cerebral artery occlusion model and physiological levels of estradiol replacement therapy. The results demonstrate that estradiol exerts profound protective effects against ischemic brain injury induced by cerebral artery occlusion and that this protective action correlates with changes in the level of gene expression of estradiol receptors and members of the Bcl-2 family. These data suggest that estrogen replacement therapy may provide important protection against age- and disease-related degenerative processes in the brain.