[Evaluation of N-acetyl-L-tryptophan in long-term intravenous administration in growing rats]

Utilization of N-acetyl-L-tryptophan as a source of L-tryptophan is tested in growing rats receiving total parenteral nutrition for twelve days. The three solutions tested are isonitrogenous and isocaloric. Solution 1 contains an adequate amount of L-tryptophan, while in solution 2 two thirds of the L-tryptophan are substituted by a corresponding amount of glycine. In solution 3, the entire L-tryptophan is replaced by N-acetyl-L-tryptophan. Weight gain and nitrogen balance are similar under the infusion with either the adequate amount of L-tryptophan or the N-acetyl-L-tryptophan. The solution 2 in which two thirds of the L-tryptophan are replaced by glycine yields significantly lower results for weight gain and nitrogen retention. The results indicate that tryptophan from N-acetyl-L-tryptophan, when given intravenously, is utilized by the rat for protein synthesis and growth as well as free tryptophan.