Department of Physiology, Women and Children’s Health Research Institute, Cardiovascular Research Centre, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
Endocrinology. 2012 Aug;153(8):3940-8. doi: 10.1210/en.2012-1071. Epub 2012 Jun 14.
Ovarian dysfunction at any age is associated with increased cardiovascular risk in women; however, therapeutic effects of exogenous estrogens are age dependent. Estradiol (E2) activates neuronal nitric oxide synthase (nNOS) in vascular cells. Because nNOS is prone to uncoupling under unfavorable biochemical conditions (as seen in aging), E2 stimulation of nNOS may lack vascular benefits in aging. Small mesenteric arteries were isolated from female Sprague Dawley rats, 3 or 12 months old, who were ovariectomized (Ovx) and treated with placebo or E2 for 4 wk. Vascular relaxation to exogenous E2 (0.001-100 μmol/liter) ± selective nNOS inhibitor (N-propyl-l-arginine, 2 μmol/liter) or pan-NOS inhibitor [Nω-nitro-l-arginine methyl ester (l-NAME), 100 μmol/liter] was examined on wire myograph. NOS expression was measured by Western blotting in thoracic aortas, in which superoxide generation was detected as dihydroethidium (DHE) fluorescence. E2 relaxations were impaired in Ovx conditions. E2 treatment (4 wk) normalized vascular function in young rats only. Both l-N-propyl-l-arginine and l-NAME blunted E2 relaxation in young controls, but only l-NAME did so in aging controls. NOS inhibition had no effect on acute E2 relaxation in Ovx rats, regardless of age or treatment. nNOS expression was similar in all animal groups. However, nNOS inhibition increased DHE fluorescence in young controls, whereas it reduced it in aging or Ovx animals. In E2-treated animals of either age, superoxide production was NOS independent. In conclusion, nNOS contributed to vascular relaxation in young, but not aging rats, where its enzymatic function shifted toward superoxide production. Thus, nNOS dysfunction may explain a mechanism of impaired E2 signaling in aging conditions.
任何年龄的卵巢功能障碍都与女性心血管风险增加有关；然而，外源性雌激素的治疗效果取决于年龄。雌二醇 (E2) 可激活血管细胞中的神经元型一氧化氮合酶 (nNOS)。由于 nNOS 在不利的生化条件下容易解偶联（如在衰老中所见），因此 E2 对 nNOS 的刺激可能在衰老中缺乏血管益处。从小鼠分离出 3 或 12 个月大的雌性 Sprague Dawley 大鼠的肠系膜小动脉，这些大鼠被卵巢切除 (Ovx) 并接受安慰剂或 E2 治疗 4 周。在 wire myograph 上检测外源性 E2（0.001-100 μmol/l）±选择性 nNOS 抑制剂（N-丙基-L-精氨酸，2 μmol/l）或 pan-NOS 抑制剂[Nω-硝基-L-精氨酸甲酯 (l-NAME)，100 μmol/l]对血管舒张的作用。在胸主动脉中通过 Western blot 测量 NOS 表达，其中超氧化物生成被检测为二氢乙啶 (DHE) 荧光。E2 舒张在 Ovx 条件下受损。E2 治疗（4 周）仅使年轻大鼠的血管功能正常化。在年轻对照组中，l-N-丙基-L-精氨酸和 l-NAME 均使 E2 舒张减弱，但在衰老对照组中仅 l-NAME 使 E2 舒张减弱。NOS 抑制对年轻 Ovx 大鼠的急性 E2 舒张没有影响，无论年龄或治疗如何。nNOS 表达在所有动物组中相似。然而，nNOS 抑制增加了年轻对照组中的 DHE 荧光，而在衰老或 Ovx 动物中则减少了 DHE 荧光。在任何年龄的 E2 处理动物中，超氧化物的产生都是与 NOS 无关的。总之，nNOS 有助于年轻大鼠的血管舒张，但在衰老大鼠中没有作用，其酶功能向超氧化物产生转移。因此，nNOS 功能障碍可能解释了衰老条件下 E2 信号转导受损的机制。
