[Nuclear 3,5,3'-triiodothyronine receptors in circulating human lymphocytes in normal, hyper-and hypothyroid...

The relationship between nuclear receptors and thyroid function state has not been elucidated. We have determined the circulating lymphocyte nuclear T3R in normal subjects, in patients with hyper-and hypothyroidism and in hypothyroid patients on thyroid hormone substitution treatment, with 10 cases in each group. In hyperthyroid and hypothyroid patients, the nuclear affinity (Kd) for T3 was similar to that of normal subjects. In hyperthyroidism nuclear T3 MBC was unaltered, whereas in hypothyroidism the MBC was significantly increased to 8.06 +/- 0.80 fmol/micrograms DNA, being 2.1 times that of the control group. In hypothyroid patients treated with 90-120 mg desiccated thyroid extract daily the nuclear MBC was 4.34 +/- 0.72 fmol/micrograms DNA, being not different from that observed in euthyroid subjects. It was found that the nuclear T3 MBC was negatively correlated with serum levels of T3, T4, FT3, FT4 and rT3, but positively correlated with serum TSH concentration in hypothyroid patients. These results indicate hormonal modulation of the nuclear T3R which exhibits up regulation in hypothyroidism. The increase in nuclear T3R number might reflect a compensatory mechanism to the decreased serum concentrations of thyroid hormones.