Exercise Prior To Acute Myocardial Infarction Improves Cardiac Healing Through Alterations In Heart Energy Metabolism

Abstract

Heart metabolism is predominantly aerobic, with the majority of energy being derived from fat oxidation. During ischemia, however, glycolytic metabolism is stimulated and contributes significantly to cardiac energy supply. Although strenuous exercise stimulates glycolysis, chronic training upregulates fat utilization. These metabolic alterations may contribute to the cell survival during ischemia caused by acute myocardial infarction (AMI). PURPOSE: To study the effect of exercise training conducted prior to AMI on the activity of key enzymes involved in heart energy metabolism during left ventricular (LV) remodeling. METHODS: Male Sprague Dawley (n=28) rats underwent 3 weeks of swimming exercise training (90 min, 5 days/wk), or remained sedentary. At the end of the training/ sedentary period, all rats were subjected to AMI induced by surgical ligation of the left coronary artery and thereafter remained sedentary during a 4-week recovery period and thereafter sacrificed. Trans-thoracic echocardiography was performed on each group at the end of the exercise/ sedentary period; 24 hours following AMI; and 4 weeks following AMI. At sacrifice, hearts were harvested and assayed for enzyme activities using standard spectrophotometric and isotope techniques. RESULTS: 3 weeks of exercise training prior to AMI resulted in higher shortening fractions compared to the 3 wk sedentary group at 24h-post-AMI (38.4±12.5% vs. 23.7±7.4;p<0.05)and4weeksafterAMI (39.1±12.5% vs. 22.6±7.9; p<0.05). Although hexokinase activity was higher in the trained group, the difference was not statistically significant (30±3 vs. 25±3 μmol/g dw/min; p=0.09). However, the activities of the remaining enzymes were significantly higher in the prior-exercised group: glycogen phosphorylase (63±6 vs. 40±5 μmol/g dw/min; p<0.03), citrate synthase (305±22 vs. 216±26 μmol/g dw/min; p<0.03), and 3-Hydroxyacyl-CoA dehydrogenase (171±26 vs. 79±8 μmol/g dw/min; p<0.02). CONCLUSIONS: 3 weeks of exercise training prior to AMI was sufficient to increase the activity of key enzymes associated with carbohydrate and fat oxidation 4 weeks following AMI: indicating improved metabolic response of the trained heart to injury, that may contribute to cardiac function during LV remodeling.