The effects of high intensity exercise on muscle and plasma levels of alpha-ketoisocaproic acid |
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Authors: | Roger A Fielding William J Evans Virginia A Hughes Lyle L Moldawer Bruce R Bistrian |
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Institution: | (1) Human Physiology Laboratory, U.S.D.A. Human Nutrition Research Center on Aging at Tufts University, 02111 Boston, MA;(2) Cancer Research Institute, New England Deaconess Hospital, 02215 Boston, MA, USA |
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Abstract: | Summary Alpha-ketoisocaproic acid (KIC) is the product of the transamination of the indispensable amino acid leucine, which is the
first step in the complete degradation of leucine. To determine the effects of intense exercise on muscle and blood levels
of KIC, 7 male volunteers performed cycle exercise to exhaustion. After pedaling at an intensity of 90 W for 3 min, the load
was increased by 60 W every 3 min until volitional fatigue. Muscle biopsies were obtained prior to and immediately after exercise
and rapidly frozen for later determination of KIC. During exercise, blood lactate levels increased as expected, while plasma
KIC levels did not change. Following exercise, plasma KIC levels rose significantly with peak values occurring 15 min after
exercise and did not return to pre-exercise values until 60 min after exercise. In contrast, muscle KIC levels increased during
exercise from a pre-exercise mean of 49.4±4.1 Μmol · kg−1 wet wt to 78.1±6.5 Μmol · kg−1 after exercise, an average increase of 48% (P<0.05). These data indicate that during intense exercise, leucine transamination in muscle may continue at a faster rate than
the decarboxylation of KIC. In addition, plasma levels of KIC did not reflect the intracellular accumulation of KIC during
exercise, suggesting a delay in the diffusion of KIC from muscle. |
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Keywords: | Intense exercise Alpha-ketoisocaproic acid Leucine Indispensable amino acid |
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