INCREASE IN RED-BLOOD-CELL TRIIODOTHYRONINE UPTAKE IN UNTREATED UNIPOLAR MAJOR DEPRESSED-PATIENTS COMPARED TO HEALTHY-VOLUNTEERS

1. Kinetic parameters of red blood cell (RBC) L-triiodothyronine (T3) initial uptake (Vmax, maximal velocity and Km, Michaelis constant) wer e determined in 34 untreated inpatients suffering from unipolar depres sion and in 40 healthy volunteers. 2. Both Vmax and Km were significan tly increased in depressed patients as compared to controls. The alter ations in kinetic parameters were not associated with the severity of depression, 3. Out of the 19 depressed patients who were submitted to TRH test, 7 of them (36%) showed a blunted TRH-induced TSH response as sociated with a Vmax situated outside the control mean value +/- 1 S.D . 4. The authors found a significant positive correlation between Vmax of RBC L-T3 and L-tryptophan (TRP) uptakes which is in agreement with the assumption that L-T3 and L-TRP share a common carrier system at t he erythrocyte level. 5. The results indicate that the uptake of L-T3 by RBC is increased in major depression. These transport perturbations might reflect alterations in the plasmatic metabolism of L-T3. Evalua tion of RBC L-T3 uptake could be useful in a best biological character ization of the depressed patients with regard to their thyroid functio n.