Amino acid nitrogen handling by hind leg muscle of the rat during exercise

The arterio-venous differences and balance of amino acids across the hind leg of rats were measured during an intense bout of exercise in a treadmill, as well as in the subsequent recovery period. The size and composition of muscle amino acid pool were also determined using another series of animals. Finally, the amino acid composition of hind leg protein was determined and computed. During intense exercise and recovery, the muscle was a net contributor of amino acids to the bloodstream, the rates being higher during exercise than in recovery. This efflux was not only due to changes in pool size, but implied the hydrolysis of protein, in the range of 20-25 micrograms.min-1.g-1 during exercise. Branched chain amino acids were metabolized during exercise, but mainly during recovery. During exercise, there was also an increase in alanine and glutamine pool buildup and efflux. In conclusion, the data presented show that protein--and amino acid--metabolism in the exercising muscle are not as dormant as usually accepted, because branched chain amino acids are actively oxidized and the efflux of alanine, glutamine and other amino acids is maintained thanks to the net hydrolysis of protein.