Phenylacetic acid excretion in schizophrenia and depression: the origins of PAA in man.

Urinary phenylacetic acid (PAA) excretion was found to be decreased in a group of chronic schizophrenic patients, particularly in a nonparanoid subtype. No significant change in PAA excretion was observed in a group of 21 unipolar depressed patients. Urinary PAA was studied following the administration of phenylethylamine, monoamine oxidase inhibitors, a dopa decarboxylase inhibitor, a low phenylalanine diet, and phenylalanine loads in several groups of psychiatric patients and normal volunteers. While Phenylethylamine ingestion increased urine PAA, inhibition of both phenylethylamine metabolism and synthesis failed to alter urine PAA. These studies suggest that urine PAA is primarily derived from phenylalanine transamination or pathways not involving monoamine oxidase or both. The observed decrease in PAA excretion in some schizophrenic patients may reflect an alteration in this pathway. The high phenylethylamine excretion previously reported in some chronic schizophrenic patients is not directly related to the observed low PAA excretion. Therefore measurement of urine PAA is not expected to be useful in assessing any phenylethylamine abnormalities in psychiatric disorders. The possible contribution of reduced phenylalanine transamination and its subsequent increased availability for the possible synthesis of phenylethylamine in schizophrenia is discussed.