Cardiac glycogenolysis in trained and untrained ischemic rat hearts

The effect of induced myocardial ischemia on cardiac glycogen utilization was investigated in trained and untrained male Sprague-Dawley rats. Following a 12 to 15 week endurance training program, myocardial ischemia was induced by ligation of the left coronary artery. Prior to and at 5 min intervals following ligation, affected tissues of five trained and untrained animals were removed, frozen in liquid nitrogen, and analyzed for glycogen and lactic acid. The glycogen content for both groups declined significantly (p less than 0.05) during the first 5 min, 38% and 15% for the trained and untrained, respectively, with a concomitant rise in the lactic acid of 150% and 40%. Overall, the cardiac lactate in the trained hearts was lower (p less than 0.05) than in untrained hearts but the pattern of response was the same. During the final 5 min of ischemia, cardiac glycogen rose in the trained hearts and declined in the sedentary hearts. The difference between the two groups at 30 min was significant (p less than 0.05). The results show that trained and untrained rat hearts utilize glycogen differently but produce similar quantities of lactic acid during brief periods of myocardial ischemia. Similar lactate despite greater glycogen utilization may indicate reduced anaerobic stress in the trained rat heart.