Estradiol reduces cytochrome c translocation and minimizes hippocampal damage caused by transient global ischemia in rat

It is well-established that 17β-estradiol (17β-E ₂) confers neuroprotection to male and female rats exposed to focal cerebral ischemia, while less is known about the effects of the hormone under conditions of transient global ischemia. Since translocation of cytochrome c from the mitochondria to the cytosol is a critical step in apoptotic cell death after cerebral ischemia, we have investigated whether 17β-E ₂ interferes with such mechanism to exert neuroprotection. Global ischemia, induced in male Wistar rats by 5-min 4 vessel occlusion (4VO), resulted in a significant increase of cytosolic cytochrome c (cyt-c) levels as detected by Western blotting at 6 h after reperfusion. 17β-E ₂ (0.2 mg/kg, i.p.) given 1 h before ischemia minimized cytochrome c translocation and the latter effect was partially reversed by tamoxifen (0.25 mg/kg, i.p.). Bilateral cell counting revealed that delayed hippocampal damage typically caused by 4VO was abolished by 17β-E ₂ and this was partially reversed by tamoxifen in the CA3 subregion, but not in CA1/CA2 or CA4. These findings provide the original observation that 17β-E ₂ reduces delayed hippocampal damage caused by 4VO in male rats and blocks cytochrome c translocation during the early stages of neuronal death, thus providing an important mechanism involved in estrogen-mediated neuroprotection.