Potential molecular targets on which methylene blue acts to promote its effects on cardiac electrophysiology, myocardial injury, and oxidative stress in spontaneously hypertensive rats submitted to cardiac ischemia and reperfusion

Figure 1. The prevalence of ventricular arrhythmias (VAs), atrioventricular block (AVB), and lethality (LET) in the ISQ+MB, MB+ISQ, SS+CIR, and sham groups. Compared to the SS+CIR group, the MB+ISQ group showed a significant increase in VA, AVB, and LET. Comparing ISQ+MB, which was given after ischemia but before reperfusion, to SS+CIR, revealed a significant decrease in VA, AVB, and LET. VA, AVB, and LET were absent in sham rats. Fisher’s exact test was utilized to compare the data.

Figure 2. Histopathological examination of the heart tissue of rats from the experimental groups sham, SS+CIR, MB+ISQ, and ISQ+MB is shown in representative photomicrographs. The myocardium in the sham group is distinguished by striated cells with well-centralized nuclei of normal size and color, as well as the lack of necrosis. The SS+CIR group has severe coagulation-induced necrosis, characterized by pyknotic cells (decentralized nuclei and chromatin condensation), a significant proportion of cells experiencing karyolysis (nucleus absence and cytoplasmic eosinophilia), swelling, and vacuolization. Like this, the MB+ISQ group exhibits severe coagulation-induced necrosis, severe tissue loss, myocytolysis, muscle fiber swelling (a reversible increase in cell volume brought on by water accumulation, ionic imbalance), vacuolation, and cells with reduced nuclei or karyolysis. In contrast, the myocardium in the MB+ISQ group exhibits modest coagulation-induced necrosis, along with mild karyolysis, swelling, and the lack of vacuolization, yet a significant portion of the striated cells (hematoxylin and eosin at 400× magnification) are preserved.

Figure 3. Serum concentrations of the myocardial injury marker CK-MB (U/L). Treatment with MB before ISQ increased the serum concentration of CK-MB when compared to the other groups. Analysis of variance and Tukey’s post hoc test were used to compare the data, which are displayed as scatterplots with the mean ± standard error of the mean.

Figure 4. The amounts of LH, a biochemical indicator of oxidative stress, in the heart of each experimental group. Treatment with MB before ISQ and before cardiac reperfusion decreased the cardiac concentration of LH when compared to the SS+CIR and sham groups. Analysis of variance and Tukey’s post hoc test were used to compare the results, which are presented as scatterplots with the mean ± SEM (n = 5).