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


CONCLUSIONS
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.
Blomstrand
E
E
Astrand Laboratory, University College of Physical Education and Sports, Stockholm, Sweden. eva.blomstrand@ihs.se
Møller
K
K
Secher
N H
NH
Nybo
L
L
D000328:Adult; D000596:Amino Acids / Q000378:metabolism*; D000597:Amino Acids, Branched-Chain / Q000378:metabolism; D000704:Analysis of Variance; D001786:Blood Glucose / Q000032:analysis; D001921:Brain / Q000378:metabolism*; D004040:Dietary Carbohydrates / Q000008:administration & dosage* / Q000378:metabolism; D005080:Exercise Test; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism
D000596:Amino Acids; D000597:Amino Acids, Branched-Chain; D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005230:Fatty Acids, Nonesterified; D012701:Serotonin; D014364:Tryptophan