Effect of oral HRT on ischemic cerebral vessels of young and aged rats

描述（由申请人提供）：最近的数据表明，激素替代疗法（HRT）可加重卒中的风险，但HRT对脑缺血事件发生后脑抢救的潜在益处研究较少。新出现的假设表明，绝经后开始激素替代疗法的时机可能很重要。本研究的重点是在缺血后再灌注期间HRT潜在有益作用的机制。我们已经证明，在切除卵巢的年轻大鼠中，动脉血管对血管扩张剂的反应明显下降，雌激素恢复了缺血后的扩张能力。在这些研究中，我们扩展了之前的工作，以确定口服HRT是否通过降低花生四烯酸（AA）代谢的血管舒张产物来改变脑血管反应，以及这些影响是否存在于年轻和老年雌激素缺乏的雌性大鼠中。由于女性HRT处方通常包括口服雌激素（17p-雌二醇，E），结合马雌激素（CE）和天然孕酮(P)，或甲羟孕酮（MP），我们使用临床相关剂量的E， CE， P和MP，并口服给药。我们的目标是确定口服激素替代疗法是否：1)改变基底动脉和缺血后动脉血管对血管扩张剂的反应性，如果这些影响在年轻和老年雌激素缺乏大鼠中都存在，2)改变缺血后脑血管环氧化酶-2 （COX-2）的表达和前列腺素E2、前列腺环素和凝血素的产生，3)通过COX-2介导的机制改善缺血后动脉改变直径的能力，如果这种影响在老年雌激素缺乏大鼠中存在，4)是否通过20-HETE合成调节了缺血后的头动脉血管舒张能力，以及E是否通过涉及细胞色素P450/AA代谢物的机制改善了缺血后的头动脉血管舒张能力。所有研究均采用脑缺血四血管闭塞模型；在一些研究中，封闭颅窗被用来评估颅底动脉反应的变化。为了评估脑血管雌激素受体的变化和AA产物的合成，我们分离了大脑微血管，并使用酶联免疫测定和Western Blot技术。本项目将提供新的信息，1)区分E和P在HRT中的作用，2)比较年轻和老年雌激素缺乏大鼠的反应，3)不仅关注COX-2的AA代谢物，而且关注细胞色素P450，这在脑再灌注过程中尚未得到很好的研究。

DESCRIPTION (provided by applicant): Recent data suggest that hormone replacement therapy (HRT) can worsen risk for stroke, but the potential benefits of HRT on brain rescue once a cerebral ischemic event occurs have been poorly studied. Emerging hypotheses suggest that timing at which HRT is initiated after menopause might be important. This study focuses on mechanisms underlying the potential beneficial effects of HRT during postischemic reperfusion. We have shown that pial vascular reponses to vasodilators are markedly depressed in young ovariectomized rats and that estrogen restores postischemic dilatory capacity. In these studies, we extend our previous work to determine if oral HRT alters cerebrovascular responses by decreasing vasodilatory products of arachidonic acid (AA) metabolism and if these effects are present in young and aged estrogen-deficient female rats. Because HRT prescribed for women often includes oral estrogen (17p-estradiol, E), conjugated equine estrogen (CE) and natural progesterone (P), or medroxyprogesterone (MP), we use clinically relevant dosages of E, CE, P, and MP, and administer the drugs orally. We aim to determine if oral HRT: 1) alters basal and postischemic pial vessel reactivity to vasodilators and if these effects are present in both young and aged, estrogen-deficient rats, 2) alters postischemic cerebral vessel expression of cyclooxygenase-2 (COX-2) and production of prostaglandin E2, prostacyclin, and thromboxane, 3) improves postischemic pial artery capacity to change diameter via COX-2-mediated mechanisms and if this effect is present in aged, estrogen-deficient rats, and to ascertain 4) if depressed postischemic pial artery vasodilator capacity is modulated by 20-HETE synthesis and if E improves postischemic pial artery vasodilatory capacity via mechanisms involving cytochrome P450/AA metabolites. All studies use a 4-vessel occlusion model of cerebral ischemia; in some studies, a closed cranial window is used to evaluate changes in pial artery responses. To evaluate changes in cerebrovascular estrogen receptors and synthesis of AA products, we isolate cerebral microvessels and use enzyme-linked immunoassay and Western Blot techniques. This project will provide novel information by 1) distinguishing the effects of E from P in HRT, 2) comparing responses between young and aged, estrogen-deficient rats, 3) focusing not only on AA metabolites of COX-2, but also on cytochrome P450, which have not been well studied during cerebral reperfusion.