Research Of Mitochondrial Mechanism On UrocortinⅠ Pretreatment Of Myocardial Ischemia–reperfusion Injury

Objective::To investigate the mitochondrial mechanism of cardioprotective effect ofUrocortin I pretreatment on myocardial cell.Methods: Rat model of ischemic reperfusion injury was prepared using the Langendorffisolated heartperfusion system.Healthy SD48male rats were randomly divided into fourgroups: normal group (Nor group), Ischemia group(I/R group), UrocortinⅠpretreatmentgroup(Ucn Ⅰgroup),5-HD antagonism group(5-HD+UcnⅠ group).Nor group: perfuseKerbs-Henseleit buffer continuously for155minutes. I/R group: perfuse ST. Thomascardioplegic solution at the temperature of4℃before global cardiac ischemia for40minutes at the temperature of32℃, then reperfuse for60minutes. UcnⅠ group: perfuseK-H buffer for30minutes before ischemia, the rest managements are same with I/R group.5-HD+UcnⅠ group: perfuse K-H buffer containing5-HD before UcnⅠ pretreatment, therest managements are same with UcnⅠ group. The following indexes of the four groupsare evaluated at the end of equilibrium, before ischemia, at the end of reperfusion,respectively.(1) Indexes of heart function: heart rate (HR), left ventricular end-diastolicpressure (LVDEP), left ventricular developed pressure (LVDP) and maximumdp/dt(dp/dtmax).(2) Extract mitochondria from ventricular tissues, analyze respiratoryfunction and respiratory enzyme activity using oxygen electrode.(3) Microstructures ofmyocardial cell were scanned by transmission electron microscope.2. Isolate myocardial cells of adult rat using the MPA isolated heartperfusion system.Divide the same batch of myocardial cells into four groups after having cultured for24hours: Nor group, I/R group, UcnⅠ group,5-HD+UcnⅠ group. Nor group was culturedcontinuously for155minutes while other groups experienced anoxia for40minutes andreoxygenation for60minutes. UcnⅠ was added to UcnⅠgroup for30minutes beforeanoxia.5-HD was added to5-HD+UcnⅠ group before adding UcnⅠ,the restmanagements are same with UcnⅠ group. Evaluate the following indexes at the end of reoxygenation.(1) changes of mitochondrial membrane potential are detected by laserscanning confocal microscope.(2) analyze changes of myocardium ATP contents by highperformance liquid chromatography.Result:1. Indexes of heart function: at the end of reperfusion, HR、LVDP、LVEDP、maximum dp/dt in UcnⅠ group are smaller than those in Nor group（P＜0.05）,but aresuperior to I/R group and5-HD+UcnⅠgroup （P＜0.05）; the indexes of heart function of5-HD+UcnⅠ group are not significantly different between those in I/R group（P＜0.05）;at the end point of equilibration the cardiac function of Group Nor was better than othergroups（P＜0.05）;There was significant difference between Group UcnⅠ and GroupI/R/UcnⅠ;and there was also significant difference between Group5HD+UcnⅠ andGroup I/R.. Mitochondria respiratory function and respiratory enzyme activity: State3、RCR and theactivity of NAD+and succinate oxidase in5-HD+UcnⅠ group are significantly differentfrom those in I/R group（P＜0.05or P＜0.01）,while the activity of cytochrome C oxidaseshows no significant difference between the two groups （P＞0.05）.3.Tochondrialmembrane potential measurement: Nor group has the highest tochondrial membranepotentia（lP＜0.01）while the potential of UcnⅠ group is higher than that in I/R group and5-HD+UcnⅠ group（P＜0.05）.There is no significant difference between I/R group and5-HD+Ucn I group（P＞0.05）.4.Cardial ATP contents: Nor group has the highest contentsof ATP（P＜0.01）,the contents of ATP in UcnⅠ group are higher than those in I/R groupand5-HD+UcnⅠgroup（P＜0.05）.5-HD+UcnⅠgroup is significantly different from I/Rgroup（P＜0.05）.Conclusions: UcnⅠpretreatment can not only enhance power of cardiac muscle systole,reduce LVDEP of normal mice before ischemia, but also improve cardiac function afterischemia reperfusion. UcnⅠ pretreatment can protect the structure and function ofmitochondria, stabilize the mitochondria membrane potential, improve mitochondriarespiratory function and respiratory enzyme activity, maintain the normal processofoxidative phosphorylation and electron transference of respiratory chain, preserveATP level in myocardium tissue, guarantee the proper energy supply during ischemia-reperfusion injury. This study find that UcnⅠ plays its role through the openingof mito-KATP channel.