Abstract
Introduction: Previous stroke studies in female rodents have demonstrated that the severity of ischemic damage is differentially impacted by the estrous cycle. Estrogen is considered to be neuroprotective, but it is unclear whether this protection is dependent on the vasodilator properties of estrogen. In this study, we investigated the impact of estrus cycle stage on stroke lesion volume and whether that impact was dependent on cerebral blood flow (CBF) changes during stroke. Methods: Ischemia was induced in adult ( 10 weeks) male and female Sprague-Dawley rats by 30 minutes middle cerebral artery occlusion (MCAO) using the suture model. Prior to the stroke procedure, the phases of the estrous cycle (proestrus(P), estrus(E), metestrus(M) and diestrus (D)) were determined by vaginal smear tests in female rats. Cerebral blood flow (CBF) was measured by laser doppler and infarct volume were measured by TTC staining at d2 post-stroke. Results: Females in proestrus and diestrus (P/D) stages of the estrous cycle, which have reportedly high levels of estrogen, had significantly (p<0.05) smaller CBF decreases during ischemia and a trend for smaller infarcts than those in estrous and metestrus stages, which have lower estrogen levels. This suggests that the protective effects of estrogen may be related to effects on blood flow. However, when compared to male rats, females in P/D stages had significantly (p<0.05) smaller brain infarcts despite having similar CBF decreases. This implies that additional mechanisms are responsible for the neuroprotection observed in females when compared to males. Conclusion: Estrous cycle stage affects CBF decrease during ischemia, but this does not account for the difference in infarct size observed between male and female rats. Our study indicates that multiple mechanisms are responsible for ischemic tolerance in specific stages of the estrous cycle. Keywords: stroke, estrous cycle, CBF, estrogen
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