Click on image to view larger version.

Figure 1 Experimental protocol for five repeated-stress groups. After two sessions of exercise, whole-body hyperthermia or tumor necrosis factor (TNF)-alpha injections, performed at an interval of 48 h, the rats were subjected to 20 min of left coronary artery occlusion, followed by 48 h of reperfusion. The interval between the second stimulus and ischemia was between 0.5 and 168 h. The incidence of ventricular fibrillation during ischemia and the size of myocardial infarction after reperfusion were then examined. Although not shown, in rats subjected to a single stress (three single-stress groups), the rats were subjected to 20 min of left coronary artery occlusion, followed by 48 h of reperfusion after one episode of exercise, whole-body hyperthermia or TNF-alpha injection. The interval between the single-stress stimulus and ischemia was between 0.5 and 120 h. Myocardial manganese superoxide dismutase activity was measured 0.5 to 120 h after the single-stress stimulus (single-stress group) or 0.5 to 168 h after the second-stress stimulus (repeated-stress group).