RED-BLOOD-CELL L-TRYPTOPHAN UPTAKE IN DEPRESSION - KINETIC-ANALYSIS IN UNTREATED DEPRESSED-PATIENTS AND HEALTHY-VOLUNTEERS

Kinetic parameters (V-max and K-m) of L-tryptophan (TRP) uptake into r ed blood cells (RBC) were measured in 72 drug-free depressed inpatient s and 35 healthy volunteers. Mean V-max and K-m values were not signif icantly different between patients and volunteers. The frequency distr ibutions of V-max values, however, largely differed in the two groups: V-max values were homogeneous in the volunteers while they were widel y scattered in the depressed patients. Only 15 out of the 72 depressed patients (21%) had V-max values within 1 SD from the mean control val ue. Forty-four percent of the patients (n = 32) had V-max values above the control mean + 1 SD in 11 patients and above the control mean + 2 SD in 21 patients. Thirty-five depressed patients (n = 25) had V-max values below the control mean - 1 SD in 8 patients and below the contr ol mean - 2 SD in 17 patients. High and low K-m values were observed i n combination with high and low V-max values. The alterations in kinet ic parameters were neither associated with severity of depression nor with a specific diagnostic subtype of depression. The data show abnorm alities in RBC L-TRP uptake in most depressed patients that likely ref lect a disturbance in peripheral availability of TRP on which central serotonin synthesis closely depends.