Papillary mechanics and cardiac morphology of infarcted rat hearts after training.

Infarction of the left ventricle was induced by ligation of the coronary artery in male Sprague-Dawley rats under ketamine-xylazine anesthesia. Three weeks after surgery, animals were assigned to a trained (n = 21; running at 20 m/min, 10% grade, 1 h/day, 5 days/wk) or nontrained group (n = 23) for an additional 8 wk. A third, sham-operated control group (n = 16) remained cage sedentary for 11 wk. Ventricular mass was greater in the trained and nontrained infarct groups [1,335 +/- 57.3 and 1,414 +/- 56.1 mg, respectively (mean +/- SE)] compared with the control group (1,155 +/- 50.9 mg) (P less than or equal to 0.05). The diameter of septal fibers was 13% greater in the trained and 17% greater in the nontrained infarct groups compared with control. The specific peak developed force and maximum rate of force development of left ventricular papillary muscle in vitro were 75 and 62% greater in both infarcted groups compared with the control group; these variables were unaffected by training. Myofibrillar adenosine triphosphatase activity of septum was 20% lower in both infarct groups compared with sham-operated animals. We conclude that exercise training did not alter the magnitude of morphological and physiological adaptations to infarction.