Swim Training Improves Myocardial Resistance to Ischemia in Rats

As the relationship between training and ischemic heart disease is not yet unraveled, we test the hypothesis that, in a model free from environmental, behavioural, and neuro-hormonal factors, endurance training improves myocardial resistance to ischemia. As carbohydrate metabolism is relevant for myocardial resistance to ischemia, we also test whether hyperglycemia blunts the protective effect of training. Eight-week old rats were randomly assigned to four groups (n = 6 - 8): sedentary or trained (3-week swim program, up to 2 h/day), and normal or high-carbohydrate diet (50 g/l sucrose in drinking water). Excised hearts were perfused isovolumically (flow = 15 ml/min) with Krebs-Henseleit (2 mM free Ca++, 11 mM glucose, pH 7.38 ± 0.02, PO₂ = 670 ± 6 mmHg, PCO₂ = 43 ± 1 mmHg, mean ± SE), exposed to 60 min low-flow (1.5 ml/min) ischemia, and then reperfused for 30 min (15 ml/min). In normally fed rats training increased the stroke volume index (97.5 ± 13.0 vs. 72.6 ± 6.2 µl, P = 0.05), depressed diastolic contracture (+2.3 ±2.0 vs. +24.2 ± 6.7 mmHg, P = 0.02), improved the recovery of developed pressure · heart rate (33.8 ± 2.3 vs. 24.1 ± 3.3 mmHg/min/1000, P = 0.05), and decreased arrhythmias (P = 0.05). In high-carbohydrate-fed rats training induced myocardial hypertrophy (1.95 ± 0.08 vs. 1.67 ± 0.03 g, P = 0.02) and decreased arrhythmias but did not affect stroke volume, developed pressure · heart rate, and diastolic contracture. Thus endurance training improves myocardial resistance to ischemia but a high-carbohydrate diet partially blunts this protection. The occurrence of an inducible alteration able to modulate myocardial tolerance to ischemia may give clues to extend our knowledge of ischemic preconditioning.

Isolated hearts - reperfusion injury - myocardial performance

References

• 1 Allen D G, Orchard C H. Myocardial contractile function during ischemia and hypoxia.  Circ Res. 1987;  60 153-168
• 2 Anderson P G, Allard M F, Thomas G D, Bishop S F, Digerness S B. Increased ischemic injury but decreased hypoxic injury in hypertrophied rat hearts.  Circ Res. 1990;  67 948-959
• 3 Apstein C S, Libonati J R, Varma N, Eberli F R. Exercise, diastolic function, and dysfunction. In: Balady GJ, Pina IL (eds) Exercise and heart failure. Armonk, NY; Futura Publishing Co. Inc 1997: 39-83
• 4 Bersohn M M, Scheuer J. Effect of ischemia on the performance of hearts from physically trained rats.  Am J Physiol. 1978;  3 218
• 5 Bowles D K, Farrar R P, Starnes J W. Exercise training improves cardiac function after ischemia in the isolated, working rat heart.  Am J Physiol. 1992;  263 809
• 6 Bowles D K, Starnes J W. Exercise training improves metabolic response after ischemia in isolated working rat heart.  J Appl Physiol. 1994;  76 1608-1614
• 7 Carey R A, Tipton C M, Lund D R. Influence of training on myocardial responses of rats subjected to conditions of ischemia and hypoxia.  Cardiovasc Res. 1976;  10 359-367
• 8 Cross H R, Opie L H, Radda G K, Clarke K. Is a high glycogen content beneficial or detrimental to the ischemic rat heart?.  Circ Res. 1996;  79 482-491
• 9 Cutiletta A F, Edmistion K, Dowell R T. Effect of a mild exercise program on myocardial function and the development of hypertrophy.  J Appl Physiol. 1979;  46 354-360
• 10 de Jong J W, de Jonge R, Marchesani A, Janssen M, Bradamante S. Controversies in preconditioning.  Cardiovasc Drug Ther. 1996;  10 767-773
• 11 Folsom A R, Szklo M, Stevens J, Liao F, Smith R, Eckfeldt J H. A prospective study of coronary heart disease in relation to fasting, insulin, glucose and diabetes. The Atherosclerosis Risk in Communities (ARIC) Study.  Diab Care. 1997;  20 935-942
• 12 Fuller E O, Nutter D O. Endurance training in the rat. II. Performance of isolated and intact heart.  J Appl Physiol. 1981;  51 941-947
• 13 Gyntelberg F, Rennie M J, Hickson R C, Holloszy J O. Effect of training on the response of plasma glucagon to exercise.  J Appl Physiol. 1977;  43 302-305
• 14 Kanter M M, Hamlin R L, Unverferth D V, Davis H W, Merola A J. Effect of exercise training on antioxidant enzymes and cardiotoxicity of doxorubicin.  J Appl Physiol. 1985;  59 1298-1303
• 15 Kersten J R, Schmeling T J, Orth K G, Pagel P S, Warltier D C. Acute hyperglycemia abolishes ischemic preconditioning in vivo.  Am J Physiol. 1998;  275 725
• 16 Kihlstrom M. Protection effect of endurance training against reoxygenation - induced injuries in rat heart.  J Appl Physiol. 1990;  68 1672-1678
• 17 Korge P, Mannik G. The effect of regular physical exercise on sensitivity to ischemia in the rat's heart.  Eur J Appl Physiol. 1990;  61 42-47
• 18 Libonati J R, Gaughan J P, Hefner C A, Gow A, Paolone A M, Houser S R. Reduced ischemia and reperfusion injury following exercise training.  Med Sci Sports Exerc. 1997;  29 509-516
• 19 Lown B, Wolff M. Approaches to sudden death from coronary heart disease.  Circulation. 1971;  44 130-142
• 20 McElroy C L, Gissen S A, Fishbein M C. Exercise-induced reduction in myocardial infarct size after coronary artery occlusion in the rat.  Circulation. 1978;  57 958-962
• 21 Murry C E, Richard V J, Reimer K A, Jennings R B. Ischemic preconditioning slows energy metabolism and delays ultrastructural damage during sustained ischemic episode.  Circ Res. 1990;  66 913-931
• 22 Pascoe D D, Gladden L B. Muscle glycogen resynthesis after short term, high intensity exercise and resistance exercise.  Sports Med. 1996;  21 98-118
• 23 Paulson D J, Kopp S J, Peace D G, Tow J P. Improved postischemic recovery of cardiac pump function in excised trained diabetic rats.  J Appl Physiol. 1988;  65 187-193
• 24 Rodnick K J, Mondon C E, Haskell W L, Azhar S, Reaven G M. Differences in insulin induced glucose uptake and enzyme activity in running rats.  J Appl Physiol. 1990;  68 513-519
• 25 Samaja M, Casalini S, Allibardi S, Corno A, Chierchia S. Regulation of bioenergetics in O₂-limited isolated rat hearts.  J Appl Physiol. 1994;  77 2530-2536
• 26 Samaja M, Motterlini R, Allibardi S, Casalini S, Merati G, Corno A, Chierchia S. Myocardial metabolism and function in acutely ischemic and hypoxemic isolated rat hearts.  J Mol Cell Cardiol. 1995;  27 1213-1218
• 27 Samaja M, Motterlini R, Santoro F, Dell'Antonio G, Corno A. Oxidative injury in reoxygenated and reperfused hearts.  Free Radic Biol Med. 1994;  16 255-262
• 28 Scheuer J, Stezoski S W. Effect of physical training on the mechanical and metabolic response of the rat heart to hypoxia.  Cardiovasc Res. 1972;  30 418-429
• 29 Starnes J W, Bowles D K. Role of exercise in the cause and prevention of cardiac dysfunction. In: Holloszy JP (ed) Exercise and Sport Sciences Reviews. Baltimore; Williams and Wilkens 1998: 349-373
• 30 Tune J D, Mallet R T, Downey H F. Insulin improves contractile function during moderate ischemia in canine left ventricle.  Am J Physiol. 1998;  43 1581
• 31 Winder W W, Hagberg J M, Hickson R C, Ehsani A A, McLane J A. Time course of sympatoadrenal adaptation to endurance exercise training in man.  J Appl Physiol. 1978;  45 370-374