Urinary excretion of 5-hydroxyindoleacetic acid and N1-methyl-2-pyridone-5-carboxamide by normal and phenylketonuric children.

Excretion of 5-hydroxyindoleacetic acid (5-HIAA) and N1-methyl-2-pyridone-5-carboxamide (N1MPC) was determined before and after an oral load of tryptophan in 9 phenylketonurics on free diet and with severe mental retardation and in 8 normal subject without any drugs. Before loading, excretion of these end metabolites of the serotonin and the kynurenine pathways, respectively, of tryptophan metabolism was only slightly lower in the phenylketonurics. But after loading, excretion of 5-HIAA increased more in the patients than in the controls, the reverse being true for N1MPC. These findings are interpreted as suggesting that function of the kynurenine pathway may be more disturbed in PKU than that of the serotonin one.