Zhang J, Benveniste H, Klitzman B, Piantadosi C A
Department of Medicine, Duke University Medical Center, Durham, NC 27710.
Stroke. 1995 Feb;26(2):298-304. doi: 10.1161/01.str.26.2.298.
Transient cerebral ischemia in rats results in selective loss of neuronal viability, eg, hippocampal CA1 neurons. The neurochemical variables responsible for this selective vulnerability to ischemia/reperfusion (IR) appear to involve excitatory amino acids. In brain IR, excitatory amino acid toxicity may be modulated by endogenous nitric oxide (NO.) gas. To investigate NO. in global brain IR, we measured the effects of NO. synthase (NOS) inhibition on interstitial excitatory amino acids in rats. Changes in postischemic cerebral blood flow and blood-brain barrier function also were evaluated.
Forebrain ischemia was produced by systemic hypotension and occlusion of both carotid arteries for 15 minutes. Blood flow was restored for 60 minutes by unclamping the carotids and reinfusing with blood. A microdialysis probe was placed into the cortex and hippocampus using a stereotaxic device. Interstitial glutamate concentration was measured during IR with high-performance liquid chromatography. A competitive NOS inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME), was given intraperitoneally 30 minutes before ischemia in doses of 1, 4, and 20 mg/kg. Changes in cerebral blood flow and blood-brain barrier during IR were determined using laser-Doppler flowmetry and microdialysis with sodium fluorescein.
Glutamate in the dialysate during IR increased transiently 10-fold and returned to baseline levels by 30 minutes of reperfusion. Animals treated with L-NAME 30 minutes before ischemia also showed increases in glutamate concentration during ischemia, but glutamate remained elevated during reperfusion. The increase in glutamate concentration during reperfusion caused by L-NAME was prevented by L-arginine. The administration of L-arginine and L-NAME together decreased extracellular glutamate concentration during ischemia. Cerebral blood flow decreased to about 5% of baseline values during ischemia but increased approximately fourfold relative to control values on reperfusion. The hyperemic responses after ischemia were not different between IR groups treated with or without L-NAME. Brain ischemia increased the permeability of the blood-brain barrier to fluorescein; however, this change was attenuated by L-NAME administration at 20 mg/kg.
NOS inhibition did not attenuate extracellular glutamate accumulation during ischemia and increased its concentration on reperfusion. The elevated glutamate concentration after IR in L-NAME-treated rats did not appear to be due to either a decrease in cerebral blood flow response after ischemia or increases in local blood-brain barrier permeability. For the most part, the blood-brain barrier was spared in the immediate postischemic period by L-NAME treatment. These data suggest that NO. production may oppose synaptic excitatory amino acid accumulation and presumably excitotoxicity during IR.
大鼠短暂性脑缺血会导致神经元选择性丧失活力，例如海马CA1神经元。导致这种对缺血/再灌注（IR）选择性易损性的神经化学变量似乎涉及兴奋性氨基酸。在脑IR中，兴奋性氨基酸毒性可能受内源性一氧化氮（NO.）气体调节。为研究全脑IR中的NO.，我们测量了NO.合酶（NOS）抑制对大鼠脑间质兴奋性氨基酸的影响。还评估了缺血后脑血流量和血脑屏障功能的变化。
通过全身低血压和双侧颈动脉闭塞15分钟造成前脑缺血。松开颈动脉并重新灌注血液使血流恢复60分钟。使用立体定位装置将微透析探针置于皮质和海马中。在IR期间用高效液相色谱法测量脑间质谷氨酸浓度。在缺血前30分钟腹腔注射竞争性NOS抑制剂Nω-硝基-L-精氨酸甲酯（L-NAME），剂量分别为1、4和20mg/kg。使用激光多普勒血流仪和荧光素钠微透析法测定IR期间脑血流量和血脑屏障的变化。
IR期间透析液中的谷氨酸短暂增加10倍，并在再灌注30分钟时恢复到基线水平。缺血前30分钟用L-NAME处理的动物在缺血期间谷氨酸浓度也增加，但在再灌注期间谷氨酸仍保持升高。L-精氨酸可阻止L-NAME引起的再灌注期间谷氨酸浓度增加。L-精氨酸和L-NAME一起给药可降低缺血期间细胞外谷氨酸浓度。缺血期间脑血流量降至基线值的约5%，但再灌注时相对于对照值增加约四倍。用或不用L-NAME处理的IR组缺血后的充血反应无差异。脑缺血增加了血脑屏障对荧光素的通透性；然而，20mg/kg的L-NAME给药可减弱这种变化。
NOS抑制在缺血期间并未减弱细胞外谷氨酸的积累，反而在再灌注时增加了其浓度。L-NAME处理的大鼠IR后谷氨酸浓度升高似乎不是由于缺血后脑血流反应降低或局部血脑屏障通透性增加所致。在缺血后即刻，L-NAME处理在很大程度上使血脑屏障得以保留。这些数据表明，NO.的产生可能对抗IR期间突触兴奋性氨基酸的积累及可能的兴奋性毒性作用。
