The clinical significance of disordered renal excretion of xanthurenic acid in depressive patients.

Xanthurenic acid is a metabolite of L-tryptophanicotinic acid ribonucleotide biosynthesis. The excretion of xanthurenic acid from urine 24 h after ingestion of 5 g L-tryptophan is increased in depressive patients, and 17-hydroxycorticosteroids are considered of primary importance to this disorder. However, in this study, the excretion of xanthurenic acid and 17-hydroxycorticosteroids did not correlate with the scores of the Raskin depression scale, Hamilton depression scale, Zung depression scale, or the Zung anxiety scale in depressive patients. The patients were treated with either pyridoxine plus L-tryptophan, a presumably serotonin-enhancing treatment (n = 10) or maprotiline, a noradrenaline-enhancing drug (n = 10). Repeated measurements showed no differences between treatments after 2 or 4 weeks of treatment. The improvement in xanthurenic acid excretion precedes clinical improvements in depression. The excretion of xanthurenic acid only at 2 weeks correlated significantly with the anxiety and depression scores at 4 weeks, making prediction of clinical improvement possible. The neurobiological mode of action on noradrenergic or serotonergic neurons of antidepressant medication is of questionable significance to their therapeutic effect.