Kinetics of l-tryptophan in depressive patients: A possible correlation between the plasma concentrations of l-tryptophan and some psychiatric rating scales

The plasma concentration and flux of l-tryptophan are abnormal in primary depressive patients, according to the literature. The plasma concentrations of l-tryptophan over a 6-h period after ingestion of 5 g l-tryptophan were investigated and did not differ significantly between depressive patients and controls during the absorption, distribution, and elimination phases. There was no correlation between the plasma concentrations with anxiety or depression scores, or with the excretion in urine of 17-hydroxycorticosteroids and xanthurenic acid during the 24 h after l-tryptophan. Treatment with either 125 mg pyridoxine (three times daily with meals) and l-tryptophan (3 g at 10 PM) or with maprotiline (100 mg at 10 PM) had no influence on the plasma concentrations of l-tryptophan after 2 or 4 weeks of treatment. This excludes l-tryptophan deficiency as a pathogenic factor of depression in the patients studied. No kinetic differences could be demonstrated in the depressive patients, making differences in body compartments or flux of l-tryptophan unlikely to be of pathogenic importance to depression.