Quantitative analysis of serotonin biosynthesis in endotoxemia.

Endotoxin-poisoned mice converted significantly greater quantities of tryptophan to serotonin than did normal mice. The percentage increase, approximately 10 to 15%, was the same whether mice were given only trace quantities of tryptophan or tryptophan load (20 mg of l-tryptophan). The increased serotonin synthesis was accompanied by a decreased flow of tryptophan into the kynurenine pathway. These results indicate that excess serotonin synthesis occurs not only at dose levels of tryptophan which are toxic for endotoxin-poisoned mice but also at physiological levels of tryptophan. This latter observation may have some importance in the overall pathophysiology of endotoxin shock.