Changes in plasma amino acid distribution and urine amino acids excretion during prolonged heavy exercise

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Abstract
Venous plasma and urine amino acids and urea were measured in 10 well-trained men, aged 23-45 yr, in connection with a 70 km cross-country ski race, lasting 4.39-6.04 h, leading to slight dehydration. The estimated urea production rate during the race was of the order 7.6 .mu.mol/min, kg body wt, i.e., twice the rate for such men on ordinary protein intake, during ordinary activity, suggesting increased protein catabolism. The race led to a fall of the total plasma amino acid concentration to about 60% of the pre-race level. The branched chain amino acids (valine, iso-leucine, leucine) and alanine were markedly reduced, whereas the S-containing amino acids (taurine, cystine, methionine) and the aromatic (phenylalanine, tyrosine, tryptophan, histidine) and glutamine/glutamate were increased, unchanged or only moderately reduced. Prolonged heavy exercise is accompanied by increased protein catabolism and changes in the plasma amino acid concentrations similar to those observed during prolonged starvation, but differing from those seen at heavy exercise of less than 2 h duration or prolonged exercise of moderate intensity.

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