Influence of clofibrate on serum triptophan in man

The effect of clofibrate on free and bound tryptophan levels was tested in 8 volunteers, 5 of whom were hospitalised. Comparing the effects of the drug, administered for 5 days, with those of a placebo, given for 5 further days, after an interval of 2 days, it was observed that clofibrate lowered total plasma tryptophan by 50-70% in all subjects. The decrease is in the bound fraction and probably reflects a displacement due to the high protein binding affinity of the drug. At the same time plasma free tryptophan values increase significantly. These data confirm our previous observations in the rat, demonstrating a decrease of bound plasma tryptophan and an increase of brain tryptophan and 5-HIAA levels, and supporting the hypothesis that clofibrate increased the availability of tryptophan to brain tryptophan hydroxylase, thus stimulating serotonin synthesis.