Ryou Myoung-Gwi, Sun Jie, Oguayo Kevin N, Manukhina Eugenia B, Downey H Fred, Mallet Robert T
Department of Integrative Physiology, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107-2699, USA.
Exp Biol Med (Maywood). 2008 Jun;233(6):766-74. doi: 10.3181/0710-RM-282. Epub 2008 Apr 11.
Physiologically modulated concentrations of nitric oxide (NO) are generally beneficial, but excessive NO can injure myocardium by producing cytotoxic peroxynitrite. Recently we reported that intermittent, normobaric hypoxia conditioning (IHC) produced robust cardioprotection against infarction and lethal arrhythmias in a canine model of coronary occlusion-reperfusion. This study tested the hypothesis that IHC suppresses myocardial nitric oxide synthase (NOS) activity and thereby dampens explosive, excessive NO formation upon reperfusion of occluded coronary arteries. Mongrel dogs were conditioned by a 20 d program of IHC (FIO(2) 9.5-10%; 5-10 min hypoxia/cycle, 5-8 cycles/d with intervening 4 min normoxia). One day later, ventricular myocardium was sampled for NOS activity assays, and immunoblot detection of the endothelial NOS isoform (eNOS). In separate experiments, myocardial nitrite (NO(2)(-)) release, an index of NO formation, was measured at baseline and during reperfusion following 1 h occlusion of the left anterior descending coronary artery (LAD). Values in IHC dogs were compared with respective values in non-conditioned, control dogs. IHC lowered left and right ventricular NOS activities by 60%, from 100-115 to 40-45 mU/g protein (P < 0.01), and decreased eNOS content by 30% (P < 0.05). IHC dampened cumulative NO(2)(-) release during the first 5 min reperfusion from 32 +/- 7 to 14 +/- 2 mumol/g (P < 0.05), but did not alter hyperemic LAD flow (15 +/- 2 vs. 13 +/- 2 ml/g). Thus, IHC suppressed myocardial NOS activity, eNOS content, and excessive NO formation upon reperfusion without compromising reactive hyperemia. Attenuation of the NOS/NO system may contribute to IHC-induced protection of myocardium from ischemia-reperfusion injury.
生理调节浓度的一氧化氮（NO）通常是有益的，但过量的NO可通过产生细胞毒性过氧亚硝酸盐损伤心肌。最近我们报道，间歇性常压低氧预处理（IHC）在犬冠状动脉闭塞-再灌注模型中对梗死和致死性心律失常产生了强大的心脏保护作用。本研究检验了以下假设：IHC抑制心肌一氧化氮合酶（NOS）活性，从而抑制冠状动脉闭塞再灌注时爆炸性过量NO的形成。杂种犬通过20天的IHC方案进行预处理（FIO₂ 9.5 - 10%；5 - 10分钟低氧/周期，5 - 8个周期/天，中间间隔4分钟常氧）。一天后，采集心室心肌进行NOS活性测定以及内皮型NOS同工酶（eNOS）的免疫印迹检测。在单独的实验中，在左前降支冠状动脉（LAD）闭塞1小时后的基线和再灌注期间测量心肌亚硝酸盐（NO₂⁻）释放，这是NO形成的一个指标。将接受IHC的犬的值与未预处理的对照犬的相应值进行比较。IHC使左心室和右心室的NOS活性降低了60%，从100 - 115降至40 - 45 mU/g蛋白（P < 0.01），并使eNOS含量降低了30%（P < 0.05）。IHC将再灌注最初5分钟内的累积NO₂⁻释放从32 ± 7降至14 ± 2 μmol/g（P < 0.05），但未改变LAD充血流量（15 ± 2对13 ± 2 ml/g）。因此，IHC抑制了再灌注时的心肌NOS活性、eNOS含量和过量NO形成，而不影响反应性充血。NOS/NO系统的减弱可能有助于IHC诱导的心肌免受缺血-再灌注损伤的保护作用。
