Both regular physical exercise and low levels of H2O2 administration result in increased resistance to oxidative stress. We measured the accumulation of reactive carbonyl derivatives and the activities of proteasome complex and DT-diaphorase in cardiac muscle of trained and untrained rats after chronic i.p. administration of 1 ml t-butyl H2O2 (1 mmol/kg for 3 weeks every second day). Twenty-four rats were randomly assigned to a control group administered with saline, control administered with H2O2, and exercised administered either saline or H2O2. The activity of DT-diaphorase significantly increased in H2O2 administered and exercised groups, indicating that an increase in H2O2 levels stimulate the activity of this enzyme. The cardiac muscle of H2O2 administered nonexercised animals accumulated significantly more carbonyl than control group (P < 0.05). The exercise and H2O2 administration resulted in less oxidatively modified protein than found in nonexercised groups (P < 0.05). The peptide- like activity of proteasome complex was induced by the treatment of H2O2 and exercise and exercise potentiate the effect of H2O2. On the other hand, the chymotrypsin-like and trypsin-like activities were stimulated only by physical training and H2O2 administration. The data suggest that chronic administration of H2O2 after exercise training decreases the accumulation of carbonyl groups below the steady-state level and induces the activity of proteasome and DT-diaphorase. Hence, the stimulating effect of physical exercise on free radical generation is an important phenomenon of the exercise-induced adaptation process since it increases resistance to oxidative stress. Regular exercise training is a valuable physiological means of preconditioning the myocardium to prolonged oxidative stress. (C) 2000 Academic Press.
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