Increase in Serum Concentrations of Thyroxine-Binding Globulin and of Cortisol-Binding Globulin After the Induction of Normal Thyroid Function in Previously Hyperthyroid Patients

Serum concentrations of thyroxine-binding globulin (TBG) were determined in 36 female patients with hyperthyroidism due to either Graves' disease (n = 33), or autonomous thyroid adenomas (n = 3). After the induction of euthyroidism by antithyroid drugs, serum concentrations of TBG rose from 13.7 ± 2.4 ng/mL to 17.1 ± 2.8 ng/mL (p < 0.001) whereas those of sex hormone-binding globulin (SHBG) fell from 142.2 ± 66.4 nmol/L to 53.6 ± 21.8 nmol/L (p < 0.001). Serum concentrations of cortisol-binding globulin (CBG) rose to 42.9 ± 10.3 μg/mL (basal: 36.8 ± 9.4 μg/mL; p < 0.001) but serum concentrations of total and of free cortisol remained unchanged. Thus, thyroid hormones exert different effects on the production of various carrier proteins in vivo. Whereas they stimulate the production of SHBG, they suppress the level of CBG and of their own carrier protein, TBG.