Transporte de hormônios tireoideanos em hemácias de pacientes com hipertireoidismo ou hipotireoidismo primário

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Thyroid hormones (THs) have important effects on cellular growth, differentiation and metabolism. They bind to thyroid hormone receptors (TRs), which belong to the nuclear hormone receptor superfamily. Because TRs are located intracellularly, TH action requires its transport from the extracellular compartment into target cells. It has become increasingly clear that cellular influx and also efflux of TH is mediated by transporters, and also that it is ligand-specific and energy-dependent. Mechanisms regulating TH uptake into different tissues and the impact of thyroidal and nonthyroidal diseases in this process are not fully understood. Patients with primary hypo and hyperthyroidism show abnormalities in TH synthesis and secretion, but changes in TH transport have not been investigated so far. TH influx and efflux were investigated in erythrocytes from 9 hypothyroid patients, 14 hyperthyroid patients and 9 euthyroid volunteers (controls). 125I-T3 e 125I-T4 influx was significantly reduced in erythrocytes from hypothyroid patients at 1 and 5 minutes, whereas a non significant increase at 10 minutes was observed in erythrocytes from hyperthyroid patients compared to controls. 125I-T3 efflux from erythrocytes of hypothyroid patients was reduced, and that from erythrocytes of hyperthyroid patients was increased compared to controls. 125I-T4 efflux was reduced in erythrocytes from hypothyroid patients at 5 minutes, and no change was seen in erythrocytes from hyperthyroid patients compared to controls. Euthyroidism resulting from treatment of hyperthyroid patients with radioiodine (131I) reduced 125I-T3 and 125I-T4 influx into erythrocytes. 125I-T3 efflux was significantly reduced at 30 minutes, but there was no change in intracellular 125I-T3 remnant. 125I-T4 efflux was also reduced. Erythrocytes from male and female patients showed differences in TH transport. 125I-T3 influx into erythrocytes from female hyperthyroid patients before treatment and from female controls was increased compared to erythrocytes from hyperthyroid and control males, but no gender difference was seen between hyperthyroid patients after treatment. Similar results were obtained when 125I-T4 was studied, and in this case gender differences were even more marked. 125I-T3 e 125I-T4 efflux from erythrocytes was reduced in female and increased in male controls and hyperthyroid patients. Taken together, these results suggest thyroid dysfunction is associated with changes in TH transport in erythrocytes. However, the mechanisms involved in these changes and their physiological significance remain to be defined. It is also important to note that these changes may not reflect TH uptake and efflux dynamics in other tissues, since tissue differences of the TH transport systems are suggested.

ASSUNTO(S)

thyroid hormone transport hypotiroidism hipertireoidismo transporte de hormônio tireoideano hypertiroidism hipotireoidismo medicina

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