Effect of ischemic preconditioning on free-radical centers of isolated ratheart during ischemia and at an early stage of reperfusion

The effect of ischemic preconditioning on the free-radical state of isolate d rat myocardium fixed by rapid freezing at the 25th min of normothermic to tal ischemia and thr 3rd mill or reperfusion was studied by the EPR method. It was shown that EPR spectra registered at -40 degrees C consist of two f ree-radical signals: of the semireduced forms of ubiquinone and flavine coy nzymes. It was found that during ischemia and at the beginning of reperfusi on, the preconditioning results in a narrowing of the spectra (as compared with control) due to all increase in the narrow ubisemiquinone EPR signal p ortion, and a decrease in the total concentration of free-radical centers: by 16% in the case of ischemia, and 23% in the case of reperfusion. It was concluded that in both cases the changes were due to a decrease in the conc entration of myocardial flavosemiquinones as a result of ischemic precondit ioning. We registered the microwave power saturation curves for these two s tages, which corresponded to control and ischemic preconditioning. In the c ase of ischemia these dependences had similar shapes; however, in the case of reperfusion they differ from each other due to changes in the relative i ntensities of the EPR signals from ubisemiquinone and flavosemiquinones in the integral myocardial free-radical spectra.