Sun Hong, Patel Kaushik P, Mayhan William G
Department of Physiology and Biophysics, University of Nebraska Medical Center, Omaha 68198-4575, USA.
Alcohol Clin Exp Res. 2002 May;26(5):663-70.
Although chronic alcohol consumption impairs endothelial nitric oxide synthase-dependent reactivity of cerebral arterioles, the effect of alcohol consumption on vasodilation in response to activation of neuronal nitric oxide synthase (nNOS) has not been examined. Thus, our first goal was to determine whether chronic alcohol consumption impairs nNOS-dependent reactivity of pial arterioles. Our second goal was to examine potential mechanisms for impaired responses of pial arterioles during chronic alcohol consumption.
Sprague Dawley rats were fed liquid diets with or without alcohol for 8 to 12 weeks. By using intravital microscopy, we measured the diameter of pial arterioles in response to nNOS-dependent agonists--NMDA and kainate (KA)--in the absence and presence of N(G)-monomethyl-L-arginine (L-NMMA) or 7-nitroindazole (7-NI). We also measured responses of pial arterioles to nitroglycerin. Next, using Western blot analysis, we measured protein levels of the NMDA receptor subunit, KA receptor subunit, and nNOS protein in cerebral microvessels, parietal cortex, cerebellum, and brainstem of non-alcohol-fed and alcohol-fed rats.
Topical application of NMDA (100 and 300 microM) and KA (100 and 300 microM) produced dose-related dilation of pial arterioles in non-alcohol-fed and alcohol-fed rats. However, the magnitude of vasodilation in response to NMDA and KA, but not nitroglycerin, was significantly less in alcohol-fed compared with non-alcohol-fed rats. Topical application of L-NMMA (10 microM) or 7-NI (10 microM) significantly inhibited dilation of pial arterioles in response to NMDA and KA in non-alcohol-fed rats. In alcohol-fed rats, only NMDA-induced vasodilation was inhibited by L-NMMA. In addition, we found that NMDA receptor subunit and KA receptor subunit protein levels increased in the parietal cortex and cerebellum of alcohol-fed compared with non-alcohol-fed rats. However, no significant difference in protein level of nNOS was observed between non-alcohol-fed and alcohol-fed rats.
Our findings suggest that chronic alcohol consumption impairs nNOS-dependent dilation of pial arterioles via a mechanism that appears to be unrelated to quantitative changes in NMDA receptors, KA receptors, or nNOS. Because the regulation of cerebral blood flow is influenced by neuronal activation, impaired reactivity of cerebral blood vessels to neuronal activation may contribute to the pathogenesis of cerebrovascular disorders observed during chronic alcohol consumption.
尽管长期饮酒会损害脑动脉内皮型一氧化氮合酶依赖性反应性，但饮酒对神经元型一氧化氮合酶（nNOS）激活后血管舒张的影响尚未得到研究。因此，我们的首要目标是确定长期饮酒是否会损害软脑膜动脉的nNOS依赖性反应性。我们的第二个目标是研究长期饮酒期间软脑膜动脉反应受损的潜在机制。
将Sprague Dawley大鼠喂以含或不含酒精的液体饮食8至12周。通过活体显微镜检查，我们在不存在和存在N（G）-单甲基-L-精氨酸（L-NMMA）或7-硝基吲唑（7-NI）的情况下，测量了软脑膜动脉对nNOS依赖性激动剂——N-甲基-D-天冬氨酸（NMDA）和红藻氨酸（KA）的直径反应。我们还测量了软脑膜动脉对硝酸甘油的反应。接下来，使用蛋白质印迹分析，我们测量了未饮酒和饮酒大鼠的脑微血管、顶叶皮质、小脑和脑干中NMDA受体亚基、KA受体亚基和nNOS蛋白的水平。
局部应用NMDA（100和300微摩尔）和KA（100和300微摩尔）可使未饮酒和饮酒大鼠的软脑膜动脉产生剂量相关的扩张。然而，与未饮酒大鼠相比，饮酒大鼠对NMDA和KA而非硝酸甘油的血管舒张幅度明显较小。局部应用L-NMMA（10微摩尔）或7-NI（10微摩尔）可显著抑制未饮酒大鼠软脑膜动脉对NMDA和KA的扩张。在饮酒大鼠中，只有NMDA诱导的血管舒张被L-NMMA抑制。此外，我们发现与未饮酒大鼠相比，饮酒大鼠顶叶皮质和小脑中NMDA受体亚基和KA受体亚基蛋白水平增加。然而，未饮酒和饮酒大鼠之间nNOS蛋白水平未观察到显著差异。
我们的研究结果表明，长期饮酒通过一种似乎与NMDA受体、KA受体或nNOS的定量变化无关的机制损害软脑膜动脉的nNOS依赖性扩张。由于脑血流量的调节受神经元激活影响，脑血管对神经元激活的反应性受损可能有助于解释长期饮酒期间观察到的脑血管疾病的发病机制。
