Tryptophan Loading and Excretion of 5-Hydroxyindoleacetic Acid in Normal and Schizophrenic Subjects

In contrast to the findings of Zeller et al. (1), schizophrenic patients did not differ from normal control subjects in the rate of 5-hydroxyindoleacetic acid (5-HIAA) excretion either before or after oral administration of l-tryptophan. The excretion of 5-HIAA may be directly related to dietary tryptophan since feeding-problem schizophrenic patients excreated less 5-HIAA than either of the well-fed groups. This was not related to pyridoxin deficiency.