体外反搏对心肌梗死犬一氧化氮系统的影响

目的:探讨体外反搏对心肌梗死犬一氧化氮(NO)、一氧化氮合酶(NOS)和其基因表达的影响。方法:19只健康杂种犬随机分为对照组、缺血组和缺血+反搏组(反搏组)3组,采用开胸结扎冠状动脉左前降支的方法建立心肌缺血模型,用改良硝酸还原酶法测定心肌缺血前后血清NO含量、以及心肌组织的NO含量和NOS比活性,采用免疫组化方法检测缺血区心肌组织的NOS亚型即诱导型NOS(iNOS)和内皮型NOS(eNOS)的蛋白合成,用原位杂交方法检测构成型NOS(cNOS)信使核糖核酸(mRNA)的基因表达。结果:在冠状动脉结扎前和结扎后60min,3组犬血清NO含量均无明显差异(P＞0.05);结扎后120min和180min时,反搏组犬血清NO含量明显高于缺血组(P＜0.05)。正常组和反搏组犬心肌组织NO含量和NOS比活性均大于缺血组(P＜0.05)。免疫组化结果表明心肌缺血时iNOS蛋白合成增多,而eNOS蛋白合成减少;体外反搏对iNOS有抑制作用,对eNOS有促进作用。此外心肌缺血时cNOSmRNA的表达明显减少,反搏可促进cNOSmRNA的表达。结论:体外反搏促进NO的产生可能是其抗心肌缺血性损伤的重要机制之一。

Effects of external counterpulsation on nitric oxide system in myocardial infarction canines

AIM: To investigate the effects of external counterpulsation (ECP) on nitric oxide (NO) and nitric oxide synthase (NOS) and the expression of NOS gene in myocardial infarction canines. METHODS: Nineteen healthy dogs were randomly divided into three groups ie. controls, ischemia group, ischemia and ECP group. Serum NO concentrations and myocardium NO levels and NOS specific activity were determined by modified nitrate reductase method. The protein synthesis of sub-type NOS including inducible NOS (iNOS) and endothelial NOS (eNOS) of myocardial tissue were also determined by immunohistochemical method. The constitutive NOS (cNOS) mRNA was measured via in situ hybridization. RESULTS: 120 and 180 minutes after the ligating of LAD, serum NO concentration in ECP groups were higher than those in ischemic groups (P<0.05). The NO levels and NOS specific activity in myocardium of ischemic dogs were lower than those in controls and ECP group (P<0.05). Protein synthesis of iNOS increased and that of eNOS decreased in ischemic myocardium. But ECP could control the protein synthesis of iNOS, and increase that of eNOS. Further studies showed that the expression of cNOS mRNA decreased in ischemic myocardial tissue, ECP might promote the expression of it and regulate NOS in the gene level. CONCLUSION: The results suggested that it was one of the most important mechanisms through raising the NO levels to protect ischemic myocardium in ECP.