The Protective Effects And Mechanism Of "KVP" Cardioplegia On Immature Ischemic Myocardium

Part One: Preparation and Evaluation of Immature IschemicMyocardium ModelObjective: To explore the feasibility and evaluation method of isolated immatureischemic rat myocardium model without perfusion or perfusion with no glucose andno oxygen solution.Methods:88Sprague-Dawley rats, weighing60～80g,22±2days, both male andfemale, were randomly divided into11groups. While the control groups werecontinuously perfused with37℃Locke’s solution for200min, the other groupswere perfused with Locke’s solution for20min. And then perfusion was eitherstopped or perfused with Locke’s solution with no glucose and no oxygen for5,10,15,30or60min respectively, then reperfused for120min. During the whole process, theheart rate （HR, min-1）, tension （g）, contraction force （g）, peak systolic velocity（+dT/dtmax）, peak diastole velocity （-dT/dtmax）, and coronary flow （drop/min） weremonitored.Results: The cardiac function of the isolated immature hearts without perfusion for5,10or15minutes recovered to a normal state after reperfusion. By contrast, thecardiac function of the isolated immature hearts without purfusion for30or60minutes recovered to a state lower than the normal one after reperfusion. The cardiacfunction of the isolated immature hearts did not recover to normal when perfused withsolution without glucose or oxygen for5min following reperfusion, and much moredecreased in those isolated immature hearts perfused solution without glucose oroxygen for more than5min following reperfusion.Conclusions: The immature ischemic myocardium model can be prepared withoutperfusion or perfusing Locke’s solution without glucose or oxygen for some time. It can be evaluated by cardiac function monitored from cardiodynamic parameters.Part Two: The Protective Effects and Mechanism of “KVP”Cardioplegia on Immature Ischemic MyocardiumObjective: To observe the protective effects and mechanism of “KVP” cardioplegiaon immature ischemic myocardium and compared with ST.Thomas Ⅱ （K）cardioplegia and heart beating.Methods:32Sprague-Dawley rats were randomly divided into Control group, theheart-beating group, the K group and the KVP group. After20min of perfusion, thecontrol group were continuously perfused for140min; and the other groups wereperfused with no glucose and no oxygen Locke’s solution for15min （to prepareimmature ischemic myocardium）, then the heart-beating group was followed by a123min reperfusion. The K and KVP groups were perfused with ST. Thomas II or “KVP”solution respectively for3min, and then the perfusion stopped until60min laterreperfusion began and lasted for60min.The heart pulsatile curves were recorded andthe cardiac functional indexes were analysed. At the end of each experiment, theenzyme activity of Na⁺-K⁺-ATPase, Ca²⁺-Mg²⁺-ATPase, superoxidedismutase（SOD）of myocardium tissue were analyzed and the myocardial histopathology andultralstructure were observed.Results: Compared with the K group, the KVP group presented a lower level ofmyocardium tension, and the cardiac function recovered well after reperfusion; thelevels of the activities of myocardial Na⁺-K⁺ATPase、Ca²⁺-Mg²⁺-ATPase and SODwere higher, and the histology and ultra-structure of cardiac muscle maintained nearlynomal. Compared with the heart-beating group, the Na⁺-K⁺-ATPase,Ca²⁺-Mg²⁺-ATPase, and SOD in KVP group were higher.Conclusions: The “KVP” group possessed better protective effects, than theST.Thomas and heart-beating groups, concerning the cardiac function, myocardialmetabolism and structure on immature ischemic myocardium to tolerance theischemia-reperfusion injury.