Oxidation of lactate and acetate in rat skeletal muscle: analysis by 13C-nuclear magnetic resonance spectroscopy |
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Authors: | Bertocci, Loren A. Jones, John G. Malloy, Craig R. Victor, Ronald G. Thomas, Gail D. |
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Abstract: | Bertocci, Loren A., John G. Jones, Craig R. Malloy, RonaldG. Victor, and Gail D. Thomas. Oxidation of lactateand acetate in rat skeletal muscle: analysis by13C-nuclear magnetic resonancespectroscopy. J. Appl. Physiol. 83(1): 32-39, 1997.The balance between carbohydrate and fatty acidutilization in skeletal muscle previously has been studied in vivo byusing a variety of methods such as arteriovenous concentrationdifferences and radioactive isotope tracer techniques. However, thesemethodologies provide only indirect estimates of substrate oxidation.We used 13C-nuclear magneticresonance (NMR) spectroscopy and non-steady-state isotopomer analysisto directly quantify the relative oxidation of two competing exogenoussubstrates in rat skeletal muscles. We infused[1,2-13C]acetate and[3-13C]lactateintravenously in anesthetized rats during the final 30 min of 35 (n = 10) or 95 (n = 10) min of intense, unilateral, rhythmic hindlimb contractions.13C-NMR spectroscopy andisotopomer analysis were performed on extracts of gastrocnemius andsoleus muscles from both the contracting and contralateralresting hindlimbs. We found that1)[13C]lactate and[13C]acetate were taken up and oxidized by both restingand contracting skeletal muscles; and2) high-intensity musclecontractions altered the pattern of substrate utilization such that therelative oxidation of acetate decreased while that of lactate remainedunchanged or increased. Based on these findings, we propose that13C-NMR spectroscopy incombination with isotopomer analysis can be used to study the generaldynamics of substrate competition between carbohydrates and fats in ratskeletal muscle. |
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