Xanthine oxidase produces hydrogen peroxide which contributes to reperfusion injury of ischemic, isolated, perfused rat hearts

Three lines of investigation indicated that hydrogen peroxide (H₂O₂) from xanthine oxidase (XO) contributes to cardiac dysfunction during reperfusion after ischemia. First, addition of dimethylthiourea (DMTU), a highly permeant O₂ metabolite scavenger (but not urea) simultaneously with reperfusion improved recovery of ventricular function as assessed by ventricular developed pressure (DP), contractility (+dP/dt), and relaxation rate (-dP/dt) in isolated Krebs-Henseleit-perfused rat hearts subjects to global normothermic ischemia. Second, hearts from rats fed tungsten or treated with allopurinol had negligible XO activities (0.5 mU/g wet myocardium compared with > 6.0 mU/g in control hearts) and increased ventricular function after ischemia and reperfusion. Third, myocardial H₂O₂-dependent inactivation of catalase occurred after reperfusion following ischemia, but not after ischemia without reperfusion or perfusion without ischemia. In contrast, myocardial catalase did not decrease during reperfusion of ischemic hearts treated DMTU, tungsten, or allopurinol.