The role of alanine in the nitrogen conserving quality of the branched-chain amino acids in the postinjury state

Abstract

In a recent study from this laboratory the improved nitrogen-conserving quality of the branched chain amino acids (BCAA) in the post-traumatic state was demonstrated. A number of properties have been ascribed to the BCAA which may be responsible for these effects. In order to elucidate which of these properties ascribed to the BCAA is responsible for this nitrogen-sparing effect, three groups of rats were infused with 8% dextrose, 3% alanine in 5% dextrose, or 3% solution of all the branched-chain amino acids (100% BCAA) in 5% dextrose after undergoing laparotomy and jugular vein cannulation. The groups of animals receiving 100% BCAA showed less negative nitrogen balance and lost less weight than the animals receiving isocaloric 8% dextrose. The group receiving 100% BCAA had a significantly better nitrogen balance than the alanine group. The plasma and muscle amino acid pattern of the 100% BCAA is more nearly normal as compared with the other groups suggesting decreased amino acid efflux from muscle. That the group receiving 100% BCAA showed better nitrogen balance than the alanine group combined with the near normal plasma and muscle amino acid pattern in the 100% BCAA group suggests that the mechanism of the improved nitrogen-conserving quality of the BCAA in the post-traumatic state is not only through increased alanine production and gluconeogenesis by BCAA infusion, but is probably a combination of the BCAA being used as energy substrate in the muscle, serving as a substrate for alanine production and gluconeogenesis and blockage of amino acid efflux from the muscle.