缺血预处理通过β_2-肾上腺素受体保护心肌细胞收缩功能

β_2-adrenoreceptor mediates the cardioprotection of ischemic preconditioning on myocardial contraction in rats subjected to ischemia/reperfusion injury

本文旨在探讨缺血预处理(ischemic preconditioning,IP)对缺血/再灌注(ischemia/reperfusion,I/R)损伤心脏的保护机制,从细胞和受体水平研究β2-肾上腺素受体(β2-adrenoreceptor,β2-AR)是否参与了IP对I/R损伤心脏的保护作用。Sprague-Dawley大鼠随机分为单纯I/R组(对照组)、IP组、短暂异丙肾上腺素(isoproterenol,ISO)处理组、IP+ICI118551组、ISO+ICI118551组和ICI118551组。除对照组外,其它各组大鼠处理后均行缺血30min/复灌30min。记录心脏收缩期左心室内压上升的最大变化速率(+dp/dtmax)、舒张期左心室内压下降的最大变化速率(-dp/dtmax)及左心室内压差(difference of left ven-tricular pressure,ΔLVP,左心室收缩压-左心室舒张压)。测定冠状动脉流出液乳酸脱氢酶(lactate dehydrogenase,LDH)含量。进一步酶解分离心脏,获得单个心室肌细胞,测定其存活率和收缩功能。结果显示,IP和ISO组±dp/dtmax、ΔLVP较对照组增高;心肌细胞存活率和收缩幅度也显著升高;收缩时间(time-to-peak contraction,TTP)缩短;冠状动脉流出液LDH含量减少。选择性β2-AR拮抗剂ICI118551阻断IP和ISO的作用。各组间心肌细胞舒张50%时间(time-to-50%relaxation,R50)和舒张100%时间(time-to-100%relaxation,R100)均无明显差异。结果提示,β2-AR可能在IP对I/R损伤心脏的保护作用中发挥重要作用。

The aim of the present study is to investigate the role of β2-adrenoreceptor （β2-AR） in ischemic preconditioning （IP） in isolated rat heart model of ischemia/reperfusion （I/R）. Sprague-Dawley rat hearts were quickly removed, mounted on Langendorff apparatus, and perfused with Krebs-Henseleit （KH） solution. After the initial stabilization period, the rats were randomly divided into 6 groups including control group （perfused for an additional 20 min）, IP group （4 cycles of 5 min of ischemla followed by 5 mln of reflow）, isoproterenol （ISO） group （10 nmol/L ISO perfusion for 5 min followed by 5 min washout）, IP ＋ ICI 118551 group （55 nmol/ L ICI118551 perfusion for 5 min before and throughout IP）, ISO ＋ ICI118551 group （55 nmol/L ICI118551 perfusion for 5 min before and throughout ISO treatment）, ICI118551 group （55 nmol/L ICI118551 perfusion for 20 min）. After these treatments, all hearts were followed by 30 min of no-flow ischemia and 30 min of reperfusion. A computer-based electrophysiological recorder system was used to measure changes of the maximal rate of pressure increase in systole phase （＋dp/dtmax）, maximal rate of pressure decrease in diastole phase （-dp/dtmax）, and difference of left ventricular pressure （△LVP）. Then cardiomyocytes from these hearts were isolated by 5 mln of Ca^2＋ -free buffer perfusion and 25 min of collagenase perfusion. The ventricles were chopped and filtered. The myocytes were resuspended in KB buffer. The contraction and the viability of cardiomyocytes were measured. Lactate dehydrogenase （LDH） concen-tration in coronary effluent was assayed with assay kit. The results showed that both IP and ISO significantly increased the values of ±dp/dtmax, △LVP, the contraction and viability of cardiomyocytes, shortened the time-to-peak contraction （TTP）, and decreased the release of LDH in coronary effluent. ICI118551, a selective β2-AR antagonist, blocked these effects. Either the time-to-50% relaxation（R50） or the time-to-100% relaxation （R100） had no significant differences between groups. Our results indicate that the cardioprotection of IP was mediated by β2-AR in isolated rat hearts subjected to I/R injury.