Role of Oxygen Free Radicals in Myocardial Injury during Ischemia and Reperfusion

氧自由基（OFR）是心肌缺血再灌注损伤的重要机制之一。本研究的目的是：1）用~ 1H-NMR方法从高能磷酸盐代谢和<31>~ 1H-NMR方法从细胞内Ca ~（2+）变化<19>两个方面阐明氧自由基对糖尿病心肌损伤的机制; 2）阐明糖尿病心肌对氧自由基的反应。离体心脏短期（8 min）暴露于过氧化氢（H_2O_2）引起双相心功能不全，其特征是左室发展压一过性降低和左室舒张末期压进行性升高。我们将前者定义为心功能不全的早期成分（EC），后者定义为心功能不全的晚期成分（LC）。根据~ 1 <31>P-NMR研究，EC与糖酵解抑制有关，LC与总ATP含量的消耗有关。根据^&lt;1 ...更多信息 9、F-HMR研究显示，细胞内Ca^&lt;2+&gt;浓度（[Ca^&lt;2+]_i）从315（[]SY.+. 23 nM至701（[SY.+-.]）58 nM通过暴露于H_2O_2。[Ca^&lt;2+&gt;] i的变化与LC的时程一致，提示心肌缺血再灌注时产生的氧自由基可引起糖酵解抑制和细胞内Ca^&lt;2+&gt;超载，导致能量代谢异常，这些变化可能是导致再灌注心肌心功能不全的原因之一。OFR的损伤机制可能是膜脂过氧化导致的膜功能紊乱和蛋白质变性导致的酶失活。近年来的研究表明，糖尿病心肌对缺血再灌注损伤具有抵抗性。我们还研究了链脲佐菌素诱导的糖尿病心脏和胰岛素治疗的糖尿病心脏对H_2O_2的反应。我们观察到糖尿病心脏对外源性H_2O_2有耐受性，长期胰岛素治疗可减弱对OFR的耐受性，这可能与减轻糖酵解抑制和抑制细胞内Ca^&lt;2+&gt;超载有关。糖尿病心脏对缺血再灌注损伤的抵抗性可能与其对氧自由基的耐受性有关。少

Oxygen free radicals (OFR) has been suggested as a mechanism of the myocardial injury during ischemia and reperfusion. The purpose of this study is 1) to elucidate the mechanism of the myocardial injury induced by OFR concerning the high-energy phosphate metabolism with ^<31>P-NMR method and the intracellular Ca^<2+> changes with ^<19>F-NMR method, and 2) to clarify the response of diabetic hearts to OFR as well. The exposure of an isolated perfused heart to hydrogen peroxide (H_2O_2) for a short duration (8 min) provoked the biphasic cardiac dysfunction which is characterized by a transient depression of left ventricular developed pressure and a progressive elevation of left ventricular end-diastolic pressure. We defined the former as the early component (EC) of cardiac dysfunction and the latter as its late component (LC). According to the ^<31>P-NMR study, EC was associated with the glycolytic inhibition, and LC was related to the depletion of total ATP content. According to the ^<1 … More 9>F-HMR study, the intracellular Ca^<2+> concentration ([Ca^<2+>]_i) increaed from 315(]SY.+-.])23 nM to 701(]SY.+-.])58 nM through the exposure to H_2O_2. The alteration of [Ca^<2+>]_i was in good agreement with the time course of LC.These suggest that OFR produced during myocardial ischemia and reperfusion induce the abnormal energy metabolism due to glycolytic inhibition and intracellular Ca^<2+> overload, and these changes may be responsible for cardiac dysfunction in the reperfused myocardium. The injuring mechanism of OFR may be the disturbed membrane function due to peroxidation of membrane lipids and the enzymatic inactivation due to denaturation of proteins. Recent reports have suggested that diabetic myocardium was resistant to the ischemia-reperfusion injury. We also studied the response of streptozotocin-induced diabetic hearts and insulin-treated diabetic hearts to H_2O_2. We observed that the diabetic hearts were resistant to the exogeneous H_2O_2, and the chronic insulin treatment attenuated the tolerance to OFR.Our results indicated that its tolerance might be attributed to the attenuation of glycolytic inhibition and the suppression of intracellular Ca^<2+> overload. The resistance of diabetic hearts to ischemia-reperfusion injury might be, at least in part, associated with its tolerance to OFR. Less