ASSOCIATION BETWEEN MUSCLE ACETYL-COA AND ACETYLCARNITINE LEVELS IN THE EXERCISING HORSE

Treadmill exercise of 2-min duration and increasing intensity resulted in increased formation of acetyl-CoA and acetylcarnitine in working muscle of Thoroughbred horses. At high work intensities a plateau was reached for both acetyl-CoA (~50 μmol/kg dry muscle) and acetylcarnitine (~20 mmol/kg dry muscle). Postexercise concentrations were significantly (P < 0.001) correlated; [acetylcarnitine] = 349 · [acetyl-CoA] + 2.4. The results indicate that ~350 μmol acetylcarnitine were accumulated for every 1 μmol acetyl-CoA. Under the conditions of exercise used it is probable that most of the acetyl-CoA formed is generated through the intramitochondrial decarboxylation of pyruvate. The acetyl groups of acetyl-CoA are apparently redistributed throughout the whole cell through formation of acetylcarnitine, which readily transverses the mitochondrial membrane. Despite the redistribution, however, the close correlation between acetylcarnitine and acetyl-CoA would indicate that equilibrium was maintained and that neither acetylcarnitine transferase nor carnitine/acetylcarnitine translocase were rate limiting. There is some questions as to whether the changes observed relate directly to exercise itself or to the state in muscle 10 s or more after exercise.