Beneficial effects of exercise on l-isoproterenol induced myocardial infarction in male rats.

The effect of exercise on the severity of isoproterenol-induced acute myocardial infarction was studied in male rats. Thirty-three 100-day-old Sprague-Dawley rats were subjected to moderate treadmill exercise (65% VO2max) for 13 wk. Exercise consisted of running 15 m/min for 30 min on an 8 degree incline for 5 d/wk. Sixty-three sedentary control animals of equal age were housed with the exercising animals throughout the experiment. Growth rates of the sedentary rats (SD) were matched to exercising rats (EX) by reducing food intake. Cardiac hypertrophy was not evident after exercise training, yet significantly lower heart rates (386-421/min) were observed in EX rats. Resting arterial blood pressure was not significantly altered by exercise. In response to l-isoproterenol stress (70 mg/kg), EX and SD rats exhibited significant increases in heart rate (EX: 19%, SD: 9%), respiratory rate (EX: 39%, SD: 15%), and cardiac contractility (EX: 48%, SD: 54%). EX and SD rats exhibited severe reductions in aortic pressure (EX: 92/63 mmHg, SD: 74/48 mmHg) resulting in large declines in the double product (HR X SAP). No EX rat died from l-isoproterenol injection, but 24% of the SD rats died. Exercise was beneficial in the reduction or prevention of induced infarction and this occurred without cardiac hypertrophy.