Soukhova-O'Hare Galia, Lei Zhenmin, Falcone Jeff C, Barati Michelle T, Feitelson Jeremy B A, Rao Ch V, Fleming John T
Department of Physiology and Biophysics, University of Louisville, Louisville, KY 40292, USA.
Life Sci. 2005 Aug 26;77(15):1799-812. doi: 10.1016/j.lfs.2004.10.083.
This study was designed to test the hypothesis that endogenous estrogens decrease the expression of endothelial nitric oxide synthase (eNOS) in resistance-size bone arterioles, thereby reducing endothelium-dependent vasodilator function. Sexually mature female rats were ovariectomized to reduce endogenous estrogens. Age-matched female rats served as controls. Seven to ten days after ovariectomy, bone marrow tissue was collected from the femoral canal. Immuno-histochemistry was performed to detect expression of estrogen receptors, alpha and beta and eNOS. eNOS protein content in medullary bone arterioles was compared using Western blot analysis. Endothelial cell function was assessed by quantitating the dilation of isolated, pressurized bone arterioles in response to acetylcholine. The results indicate that the endothelium of bone arterioles from ovariectomized and control rats express ER-alpha, ER-beta and eNOS. eNOS protein content in the two groups of arterioles did not differ. However, the baseline diameter of arterioles from ovariectomized rats (63+/-4 microm) was significantly smaller than the diameter of arterioles from control rats (75+/-3 microm, p<0.05). The two groups of arterioles dilated equally in response to acetylcholine. L-NAME, an inhibitor of eNOS, almost completely abolished the dilator responses to acetylcholine, but not to sodium nitroprusside. L-Arginine restored acetylcholine-induced dilation after L-NAME treatment. Thus, arteriole dilation to acetylcholine appears to be mediated almost exclusively by NO. The smaller diameter of arterioles from ovariectomized rats suggests that endogenous estrogens exert a significant dilator influence on bone arterioles. However, the dilator influence does not appear to be mediated by an increase in eNOS expression or enhanced NO-dependent vasodilation. These results indicate that estrogens do not decrease eNOS expression or diminish NO-mediated dilation of bone medullary arterioles.
内源性雌激素会降低阻力型骨小动脉中内皮型一氧化氮合酶（eNOS）的表达，从而削弱内皮依赖性血管舒张功能。对性成熟雌性大鼠进行卵巢切除术以降低内源性雌激素水平。年龄匹配的雌性大鼠作为对照。卵巢切除术后7至10天，从股管收集骨髓组织。采用免疫组织化学法检测雌激素受体α和β以及eNOS的表达。使用蛋白质免疫印迹分析比较髓质骨小动脉中eNOS蛋白含量。通过定量检测分离的、加有压力的骨小动脉对乙酰胆碱的舒张反应来评估内皮细胞功能。结果表明，卵巢切除大鼠和对照大鼠的骨小动脉内皮均表达雌激素受体α、雌激素受体β和eNOS。两组小动脉中的eNOS蛋白含量无差异。然而，卵巢切除大鼠的小动脉基线直径（63±4微米）显著小于对照大鼠的小动脉直径（75±3微米，p<0.05）。两组小动脉对乙酰胆碱的舒张反应相同。eNOS抑制剂L-NAME几乎完全消除了对乙酰胆碱的舒张反应，但对硝普钠的反应无影响。L-精氨酸在L-NAME处理后恢复了乙酰胆碱诱导的舒张。因此，小动脉对乙酰胆碱的舒张似乎几乎完全由一氧化氮介导。卵巢切除大鼠的小动脉直径较小表明内源性雌激素对骨小动脉有显著的舒张作用。然而，这种舒张作用似乎不是由eNOS表达增加或一氧化氮依赖性血管舒张增强介导的。这些结果表明，雌激素不会降低eNOS表达或减弱骨骨髓小动脉的一氧化氮介导的舒张。
