| The purpose of this investigation was to study the training effects of endurance and high intensity treadmill running on the mechanical performance of the rat heart during reperfusion following ischemia. Fifty-one male, 12 week old, Sprague-Dawley rats, weighing 150 to 175g at the initiation of the experiment were randomly assigned into a sedentary control (n = 18), an endurance trained (n = 20), or high intensity trained (n = 13) group. A Temple University Animal Care and Use Procedure Protocol Review form was approved. Rats exercised 5 days/week for six weeks at the following intensities; endurance (20 m/min, 0% grade, 60 min/day; high (5 x 1 minute sprints at a speed of 75 m/min, at a 15% grade, interspersed with 1 minute of active recovery runs at 20 m/min, 15% grade. To maintain familiarity with the treadmill sedentary controls were run once weekly at 20 m/min, 0% grade for 10 min/day. To assess the effectiveness of the exercise training protocol, all groups were made to perform an endurance treadmill and graded intensity treadmill test. The trained rats performed significantly (p {dollar}<{dollar} 0.05), more work (kgm) on the endurance treadmill test (low, 65.77 {dollar}pm{dollar} 25.90; high 40.53 {dollar}pm{dollar} 17.65 vs. control, 21.06 {dollar}pm{dollar} 3.56) and the graded intensity test (low, 25.65 {dollar}pm{dollar} 7.02; high, 24.50 {dollar}pm{dollar} 6.58 vs. control, 15.21 {dollar}pm{dollar} 3.49). Between 48 to 72 hours following the last bout of exercise, rats were anesthetized and weighed. While being mechanically ventilated, the chest was opened and the aorta was cannulated for in situ retrograde perfusion. Hearts were trimmed of excess tissue, weighed, and transferred to a Langendorff apparatus, where a latex, intraventricular balloon was situated in the left ventricle for measures of the following: systolic, end-diastolic, and developed pressure as well as +dP/dtmax, {dollar}-{dollar}dP/dtmax, and coronary flow. The hearts were allowed to equilibrate for 20 minutes, and performance was measured at baseline, during 20 minutes of global ischemia, and during 30 minutes of reperfusion. During reperfusion, the high intensity trained hearts generated significantly higher systolic pressures, developed pressures, and +dP/dtmax, while having the lowest end-diastolic pressures (p {dollar}<{dollar} 0.05). Endurance training was not different from sedentary controls. This data suggests high intensity training attenuates the contractile dysfunction associated with stunning and that endurance training does not provide such protection. |
