Uptake of Thyroid Hormones by Erythrocytes in Relation to Depres-sion

Overview

Erythrocytes may play a role in the blood transport of thyroid hormones. There is probably somelink between changes in parameters of red blood cell uptake and depression. Thyroxin (T4) entersthe erythrocyte by free diffusion, while L-T3 by facilitated diffusion through a membrane carrier -mediated system which is saturable, stereospecific, energy and Na+-independent. Red blood cells(RBC) act as a circulating pool of triiodthyronine. In erythrocytes L-tryptophan shares the sametransport system for L-T3 (named the T system). L-T3 and L-tryptophan interact as competitiveinhibitors. In depressive patients we suppose that impaired RBC L-T3 uptake results in RBCL-tryptophan uptake and L-tryptophan plasma availibility and thus cerebral synthesis of serotonin is impaired. Changes in kinetic parameters correlate with treatment with antidepressantsand non-respondents can be distinguished from respondents. Resistance to treatment with antidepressants and changes in kinetic parameters can be due to changes of lipid structure of theRBS membrane, in case the transport protein is lipid - dependent.

Key words:
thyroid hormones, erythrocyte, transport, depression.