Quantitative analysis of tryptophan metabolites in urine of normal and endotoxin poisoned mice.

We have developed methods for quantitatively monitoring the in vivo flow of tryptophan between the kynurenine and serotonin pathways. Our data suggest that endotoxin-poisoned mice have more tryptophan flowing into the serotonin pathway than normal mice both with and without tryptophan load. It appears that the distribution of tryptophan between the serotonin and kynurenine pathways in vivo is constant over a very wide dose range and that substrate availability rather than tryptophan oxygenase activity determines the precise amounts of tryptophan which flows into the two pathways.