Effect of carbohydrate ingestion on brain exchange of amino acids during sustained exercise in human subjects

E Blomstrand, K Møller, N H Secher, L Nybo

Abstract

AIM: This study investigated the effect of prolonged exercise with and without carbohydrate intake on the brain exchange of amino acids, especially focussing on tryptophan and branched-chain amino acids (BCAA).

METHODS: Five male subjects exercised for 3 h on a cycle ergometer at 200 +/- 7 W on two occasions; either supplemented with a 6% carbohydrate solution or with flavoured water (placebo). Catheters were inserted into the right internal jugular vein and the radial artery of the non-dominant arm. The brain exchange of amino acids during exercise was calculated from the arterial-jugular venous concentration difference multiplied by plasma flow.

RESULTS: About 106 micromol (22 mg) of tryptophan was taken up by the brain during exercise in the placebo trial, whereas no significant uptake was observed in the carbohydrate trial. In accordance, the arterial concentration of free tryptophan increased from 12 +/- 1 to 20 +/- 2 micromol L(-1) during the placebo trial and was significantly higher compared with the glucose trial (14 +/- 1 micromol L(-1) at the end of exercise). Also, the arterial concentration of total tryptophan (free and albumin-bound) increased during the first 30 min of exercise in both trials, but returned to the basal level at 180 min of exercise. In both trials, BCAA were taken up by the brain while glutamine was released.

CONCLUSION: The present data show that both tryptophan and BCAA are taken up by the brain during prolonged exercise, and we suggest that the cerebral uptake of tryptophan may relate to increased synthesis of serotonin (5-HT) in the brain.

Original languageEnglish
JournalActa Physiologica Scandinavica
Volume185
Issue number3
Pages (from-to)203-9
Number of pages7
ISSN0001-6772
DOIs
Publication statusPublished - Nov 2005

Keywords

  • Adult
  • Amino Acids/metabolism
  • Amino Acids, Branched-Chain/metabolism
  • Analysis of Variance
  • Blood Glucose/analysis
  • Brain/metabolism
  • Dietary Carbohydrates/administration & dosage
  • Exercise Test
  • Fatty Acids, Nonesterified/blood
  • Humans
  • Male
  • Muscle Fatigue/physiology
  • Physical Endurance/physiology
  • Serotonin/metabolism
  • Tryptophan/metabolism

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