Effects of oxidative stress on the expression of antioxidative defense enzymes in spontaneously hypertensive rat hearts

Little is known concerning the effect of oxidative stress on the expression of antioxidative enzymes in the decompensated cardiac hypertrophy of spontaneously hypertensive rats (SHR), considered as a model of dilative cardiomyopathy in man. Superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) were characterized in isolated perfused hearts of 18 month old SHR and the age-matched normotensive control Wistar-Kyoto (WKY) rats, before and after 30 min infusion of 25 μM H2O2. After infusion of H2O2, aortic flow decreased in WKY from 26.2 ± 2.2 to 16.0 ± 0.8 ml/min (p < .05) but not in SHR (18.2 ± 1.9 vs. 20.7 ± 2.2 ml/min). This protection was related to the higher myocardial activities of GPx, MnSOD and CuZnSOD in SHR, compared with those of the WKY group. Although total SOD activity in the SHR fell after H2O2 exposure (to 1.81 ± 0.13 from 3.56 ± 0.49 U/mg of protein), catalase activity increased (to 2.46 ± 0.34 from 1.56 ± 0.29 k min−1mg−1protein), compared with the pre-infusion period (p < .05 in each case). In additional studies, hearts were subjected to 30 min of global ischemia followed by 30 min of reperfusion. The results obtained in ischemic/reperfused hearts show the same changes in enzyme activities measured as it was observed in H2O2 perfused hearts, indicating that oxidative stress is independent of the way it was induced. The higher catalase activity derived from elevated mRNA synthesis. The antioxidative system in dilative cardiomyopathic hearts of SHR is induced, probably due to episodes of oxidative stress, during the process of decompensation. This conditioning of the antioxidative potential may help overcome acute stress situations caused by reactive oxygen species in the failing myocardium.