Red blood cell triiodothyronine uptake in unipolar major depression: Effect of a chronic antidepressant treatment

1. The evolution of kinetic parameters (Vmax, maximal velocity, and Km, Mic haelis constant) of red blood cell (RBC) triiodothyronine (L-T3) initial up take was followed in 19 inpatients suffering from unipolar depression after 1 week (D7) and 4 weeks (D28) of a chronic administration of fluvoxamine, in relation with the clinical efficacy of the drug. 2. In a drug-free state (DO), Vmax (in pmol/min/10(8) cells) and Km (in nM) were significantly increased in depressed patients (Vmax +/- S.D. 1.02 +/- 0.29, p < 0.01 and Km +/- S.D. 68.8 +/- 15.4, p< 0.05; n=19) compared to h ealthy volunteers matched for age and sex (Vmax +/- S.D. = 0.82 +/- 0.15 an d Km +/- S.D. = 58.8 +/- 9.0; n = 19). When patients were dichotomized on t he basis of their treatment response, responders had kinetic parameters sig nificantly increased (Vmax +/- S.D.= 1.03 +/- 0.26, p < 0.01 and Km +/- S.D .= 71.7 +/- 18.7; p < 0.05, n = 10) compared to controls, whereas non-respo nders had not (Vmax +/- S.D. 1.00 +/- 0.33, NS and Km +/- S.D. 65.7 +/- 10. 9, NS, n = 9). 3. At D7, Vmax differed from the one of controls only in the responders (Vm ax +/- S.D.= 1.03 +/- 0.26, p< 0.01). In addition, the percentage of variat ion of the individual Vmax values during the first week of treatment was si gnificantly lower in responders than in non-responders (Delta Vmax(D7-D0) /- S.D. in % = 10.7 +/- 6.0 and 22.0 +/- 11.1, p< 0.05, respectively). 4. At D28, kinetics of L-T3 uptake normalized only in the responders (Vmax +/- S.D.= 0.91 +/- 0.13, NS;Km +/- S.D.= 65.7 +/- 7.4, NS). 5. The results indicate that both RBC L-T3 uptake at the pretreatment level and its change during the first week of fluvoxamine treatment were related to the further clinical response to the antidepressant. 6. RBC L-T3 uptake seems to be a biological correlate of the depressive sym ptomatology since the disturbances disappear only with the clinical remissi on.