Improved myocardial performance during repetitive exercise testing: The role of extracellular superoxide dismutase activity in a model of exercise-induced myocardial preconditioning

Background The aim of this study was to investigate whether endogenous antioxidant defense is involved in adaptation to myocardial ischemia in patients with coronary artery disease and severe exercise-induced myocardial ischemia. Methods Fifty patients, aged 50 to 72 years (mean, 58 6 years), with positive exercise test results underwent 4 treadmill exercise tests. Thallium-201 scintigraphy was performed during the first and the fourth testing. The second, the third, and the fourth tests were performed the next day. The time interval between the second and the third test was 15 minutes, and between the third and the fourth test, the interval was 45 minutes. Extracellular superoxide dismutase activity was measured just before and at the peak of the first and the fourth exercise test. Results The patients were divided in 2 groups according to the extent of myocardial ischemia at peak exercise of the fourth test compared with the first test. Most of the patients studied (37/50) showed improved myocardial performance during the last of the sequential exercise tests, as demonstrated with the studied exercise parameters and the extent of myocardial ischemia in thallium-scintigraphy. Extracellular superoxide dismutase activity before the lost exercise test was found to be significantly increased only in the patients who had improved myocardial performance at the last of the sequential exercise tests. Conclusion The beneficial effects of sequential episodes of exercise-induced myocardial ischemia seem to be strongly related to extracellular superoxide dismutase activity. Although there is still lack of direct evidence, our data support the theory that the favorable adaptation to repetitive exercise may represent an aspect of the clinical relevance of ischemic preconditioning in humans.