Effect of branched-chain amino acids and insulin on postinjury protein catabolism in growing animals

Muscle proteolysis continues to occur in hypercatabolic states despite the administration of carbohydrates and proteins. Recent clinical and experimental studies have demonstrated that, under catabolic conditions, treatment with either branched-chain amino acids (BCAA) or insulin may decrease negative nitrogen balance. However, the use of BCAA-enriched solutions to inhibit muscle proteolysis has never been tested in growing animals. A study was therefore undertaken to assess the effectiveness of such solutions, with or without insulin, as compared to a more balanced amino acid solution, in preventing or diminishing postinjury protein catabolism in growing animals. Fifteen-day-old rabbits, exposed to standard moderate trauma in the form of crushing the muscle mass of one rear thigh, received one of two amino acid formulations--a balanced amino acid solution (18.8% BCAA) or a 35% BCAA-enriched solution--for 96 hr. Insulin was given to subgroups of both series. The results indicate that: (1) nitrogen balance in nontraumatized animals is clearly superior when balanced amino acids are administered; (2) BCAA-enriched solutions may decrease postinjury muscle protein catabolism; (3) after trauma, insulin also has a nitrogen-conserving effect, which is demonstrated when it is combined both with BCAA-enriched (35%) and balanced amino acid (18.8%) solutions. However, a better nitrogen balance is achieved when insulin is associated with the balanced amino acid solution.