Changes of free amino acids in plasma of healthy subjects induced by physical exercise

In eight healthy men a 20-min load of 1.5 W/kg body weight on a bicycle ergometer led to a significant increase of alanine and decline of leucine. Exhausting exercise caused in the same subjects a highly significant increase of alanine and decline of isoleucine, threonine, ornithine, leucine, serine, glycine, and asparagine and glutamine. The methionine and citrulline level declines also significantly. The total amino acids practically did not change. Physical exercise led furthermore to a marked increase of serum ammonia and uric acid. Urea nitrogen changed only little and on average had rather a declining tendency. The rise of alanine suggests the existence of a glucose-alanine cycle, the drop of ornithine and citrulline is most probably associated with the inhibition of ureogenesis in the liver. The reduction of leucine and isoleucine is probably the result of the entry of these amino acids into muscle and their deamination.