Effects of exercise frequency, intensity, and duration on revascularization in the transition zone of infarcted rat hearts.

In the rat model of chronic myocardial infarction the border or "transition zone," extending 225-525 micron from the margin of the scar, is supplied by significantly fewer capillaries and characterized by an altered capillary-fiber geometry when compared with healthy rat myocardium. Four weeks of daily voluntary running can, under certain conditions, promote capillary growth and a shift in capillary-fiber geometry, such that a normal capillary supply is restored to the transition zone. However, the importance of exercise frequency, intensity, and duration for capillary growth in the transition zone has not been determined. One week after surgical occlusion of the left coronary artery, rats were divided into four groups following different protocols of voluntary exercise (running): A (2 h/day, 6 days/week for 4 weeks), B (2 h/day, 3 days/week for 4 weeks), C (2 h/day, 6 days/week for 2 weeks, followed by 2 weeks sedentary), and D (2 h/day, 6 days/week for 2 weeks). Significant improvements in capillary supply to the transition zone were associated with voluntary exercise, three separate factors being of importance. (i) An intermediate total distance run; rats that ran 5-10 km in the month restored a normal number of capillaries and a normal capillary-fiber geometry in the transition zone, whereas rats that ran either less than 5 or greater than 10 km showed no significant improvements. (ii) A balance between exercise frequency and mean distance run per 2-h exercise period; rats in group B (3 days/week) had to run twice the daily distance of those in group A (6 days/week) to obtain the same improvement in capillary supply.(ABSTRACT TRUNCATED AT 250 WORDS)