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J Appl Physiol 100: 1822-1830, 2006. First published January 19, 2006; doi:10.1152/japplphysiol.00571.2005
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Carbohydrate metabolism during prolonged exercise and recovery: interactions between pyruvate dehydrogenase, fatty acids, and amino acids

Marina Mourtzakis,1 Bengt Saltin,2 Terry Graham,1 and Henriette Pilegaard2,3

1The Copenhagen Muscle Research Centre, Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada; 2Rigshospitalet, University of Copenhagen; and 3The August Krogh Institute, Copenhagen, Denmark

Submitted 4 October 2005 ; accepted in final form 25 January 2006

During prolonged exercise, carbohydrate oxidation may result from decreased pyruvate production and increased fatty acid supply and ultimately lead to reduced pyruvate dehydrogenase (PDH) activity. Pyruvate also interacts with the amino acids alanine, glutamine, and glutamate, whereby the decline in pyruvate production could affect tricarboxycylic acid cycle flux as well as gluconeogenesis. To enhance our understanding of these interactions, we studied the time course of changes in substrate utilization in six men who cycled at 44 ± 1% peak oxygen consumption (mean ± SE) until exhaustion (exhaustion at 3 h 23 min ± 11 min). Femoral arterial and venous blood, blood flow measurements, and muscle samples were obtained hourly during exercise and recovery (3 h). Carbohydrate oxidation peaked at 30 min of exercise and subsequently decreased for the remainder of the exercise bout (P < 0.05). PDH activity peaked at 2 h of exercise, whereas pyruvate production peaked at 1 h of exercise and was reduced (~30%) thereafter, suggesting that pyruvate availability primarily accounted for reduced carbohydrate oxidation. Increased free fatty acid uptake (P < 0.05) was also associated with decreasing PDH activity (P < 0.05) and increased PDH kinase 4 mRNA (P < 0.05) during exercise and recovery. At 1 h of exercise, pyruvate production was greatest and was closely linked to glutamate, which was the predominant amino acid taken up during exercise and recovery. Alanine and glutamine were also associated with pyruvate metabolism, and they comprised ~68% of total amino-acid release during exercise and recovery. Thus reduced pyruvate production was primarily associated with reduced carbohydrate oxidation, whereas the greatest production of pyruvate was related to glutamate, glutamine, and alanine metabolism in early exercise.

alanine; pyruvate dehydrogenase kinase 4 mMRNA; carbohydrate oxidation; nitrogen balance


Address for reprint requests and other correspondence: M. Mourtzakis, Dept. Oncology, Univ. of Alberta, Cross Cancer Institute, Rm. 2237, 11560 Univ. Ave., Edmonton, Alberta, Canada T6G 1Z2 (e-mail: marinamo{at}cancerboard.ab.ca)




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