title: Carbohydrate metabolism during prolonged exercise and recovery: interactions between pyruvate dehydrogenase, fatty acids, and amino acids.
abstract: 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 (approximately 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 approximately 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.
authors.affiliation: The Copenhagen Muscle Research Centre, Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada, and Rigshospitalet, University of Copenhagen, Denmark. marinamo@cancerboard.ab.ca
authors.forename: Marina
authors.initials: M
authors.lastname: Mourtzakis
authors.forename: Bengt
authors.initials: B
authors.lastname: Saltin
authors.forename: Terry
authors.initials: T
authors.lastname: Graham
authors.forename: Henriette
authors.initials: H
authors.lastname: Pilegaard
mesh_terms: D000328:Adult; D000409:Alanine / Q000032:analysis / Q000378:metabolism; D000596:Amino Acids / Q000032:analysis / Q000502:physiology*; D001783:Blood Flow Velocity; D001786:Blood Glucose / Q000032:analysis; D050260:Carbohydrate Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005227:Fatty Acids / Q000032:analysis / Q000502:physiology*; D005263:Femoral Artery / Q000502:physiology; D005268:Femoral Vein / Q000502:physiology; D018698:Glutamic Acid / Q000032:analysis / Q000378:metabolism; D005973:Glutamine / Q000032:analysis / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D018482:Muscle, Skeletal / Q000737:chemistry / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D011494:Protein Kinases / Q000032:analysis / Q000235:genetics / Q000502:physiology; D011768:Pyruvate Dehydrogenase Complex / Q000032:analysis / Q000502:physiology*; D011773:Pyruvates / Q000032:analysis / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis
chemical_list: D000596:Amino Acids; D001786:Blood Glucose; D005227:Fatty Acids; D007328:Insulin; D011768:Pyruvate Dehydrogenase Complex; D011773:Pyruvates; D012333:RNA, Messenger; D005973:Glutamine; D018698:Glutamic Acid; D011494:Protein Kinases; C403287:pyruvate dehydrogenase kinase 4; D000409:Alanine