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

氧自由基（Oxygen free radicals， OFR）已被认为是心肌缺血再灌注损伤的机制之一。本研究的目的是：1)用^<31>P-NMR法阐明OFR诱导心肌损伤的高能磷酸盐代谢机制，用^<19>F-NMR法阐明细胞内Ca^<2+>变化机制；2)阐明糖尿病心脏对OFR的反应。将离体灌注心脏暴露于过氧化氢（H_2O_2）短时间（8分钟）可引起双相性心功能障碍，其特征是左心室发育压短暂下降和左心室舒张末期压进行性升高。我们将前者定义为心功能障碍的早期成分（EC），后者定义为心功能障碍的晚期成分（LC）。根据^<31 b> 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^<1…More 9>的F-HMR研究，细胞内Ca^<2+>浓度（[Ca^<2+>]_i）从315(]SY.+-增加。[])23 nM至701(]SY.+-。])58 nM通过暴露于H_2O_2。[Ca^<2+>]_i的变化与LC的时间过程吻合较好。提示心肌缺血再灌注过程中产生的OFR由于糖酵解抑制和细胞内Ca^<2+>过载而导致能量代谢异常，这些变化可能是再灌注心肌心功能障碍的原因。OFR的损伤机制可能是膜脂过氧化引起的膜功能紊乱和蛋白质变性引起的酶失活。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有抵抗性，慢性胰岛素治疗使其对OFR的耐受性减弱。我们的研究结果表明，其耐受性可能归因于糖酵解抑制的衰减和细胞内Ca^<2+>过载的抑制。糖尿病心脏对缺血再灌注损伤的抵抗可能，至少部分地与其对OFR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