氧自由基在缺血预处理对未成熟心肌延迟性保护机制中的作用

The effects of oxygen free radicals on delayed myocardial preservation by ischemic preconditioning in immature myocardium

目的 探讨氧自由基 (OFRs)在缺血预处理 (IP)对未成熟心肌延迟性保护 (第二窗 )机制中的作用。方法 3～ 4周龄的幼兔 30只 ,随机分为 5组 (n =6 ) :Ⅰ组 ,正常对照组 ;Ⅱ组 ,缺血 再灌注损伤组 ;Ⅲ组 ,单纯IP组 ;Ⅳ组 ,IP +L -精氨酸 (L -arginine ,30 0mg kg)组 ;Ⅴ组 ,IP +L -硝基精氨酸甲酯 (L -NAME ,10mg kg)组。建立幼兔活体心脏缺血预处理及缺血 再灌注损伤模型 ,监测左心室血流动力学变化 ,化学比色法检测心肌一氧化氮合酶 (NOS) (iNOS eNOS)活性 ,同时测定SOD活性及MDA含量。结果 缺血预处理 2 4h后 ,各组间的LVDP、±dp dtmax无显著性差异 (P >0 .0 5 ) ;缺血 再灌注 6 0min ,Ⅱ组和Ⅳ组的LVDP、+dp dtmax、-dp dtmax恢复率低于Ⅲ组和Ⅴ组 (P <0 .0 1)。缺血前 ,Ⅲ组和Ⅴ组的iNOS活性高于Ⅱ组和Ⅳ组 (P <0 .0 5 ) ;再灌注 6 0min ,Ⅲ组和Ⅴ组的eNOS活性高于Ⅱ组和Ⅳ组 (P <0 .0 5 )。缺血前和再灌注末 ,Ⅲ组和Ⅴ组的SOD活性高于Ⅱ组和Ⅳ组 (P <0 .0 5 )。结论 OFRs对IP延迟性心肌保护起到了“触发物”的作用 ,而iNOS的升高可能仅是炎性反应标记物 ,eNOS活性的升高可能是形成第二保护窗 (SWOP)的原因之一 ,外源性NO取消了SWOP的形成 ,可能与其清除了OFRs有关。

Objective To investigate the role of oxygen free radicals as the “trigger” of the delayed myocardial preservation (the second window of protection SWOP), by ischemia preconditioning (IP) in immature myocardium. Methods Thirty China white rabbits (aged 3 to 4 weeks) were randomly divided into five groups (n=6 each): groupⅠ, normal control; groupⅡ, ischemia/reperfusion injury (I/R); group Ⅲ, I/R after IP; groupⅣ, I/R after IP and adding the NO-donor L-arginine (300 mg/kg); groupⅤ, I/R after IP and adding the NOS inhibitor L-NAME (10 mg/kg). IP was performed 24 h before I/R was produced. Dynamic observations on the hemodynamics of the left ventricle and the plasma levels of SOD acvtovity, MDA content and NOS activity were made at proper time spots during the experiment. Results LVDP and ±dp/dt max showed no differences before myocardial ischemia between the 5 groups (P>0.05). After 60-min reperfusion, LVDP, +dp/dt max and -dp/dt max in groupsⅡ and Ⅳ were significantly lower than in groups Ⅲ and Ⅴ(P<0.01). The activity of plasma iNOS was higher in groups Ⅲ and Ⅴ than in groups Ⅱ and Ⅳ before ischemia (P<0.05); but after reperfusion, the activity of plasma eNOS was lower in groups and Ⅳ than in groups Ⅲ and Ⅴ(P<0.05). The activity of SOD in groups Ⅲ and Ⅴ was higher than in groups Ⅱ and Ⅳ during I/R (P<0.05). Conclusion The OFRs may effect as a “trigger” on SWOP, whereas iNOS is but a “marker”, not a “ trigger” after IP. The increase of eNOS activity contributes to the SWOP. Exogenous nitrogen monoxide, by scavenging OFRs, attenuates to SWOP in immature myocardium.