Increased insulin-like growth factor-1 receptors in thyroid tissues of Graves' disease

Insulin-like growth factor-1 (IGF-1) plays an important role in thyroid cell growth and human thyroid diseases. In order to investigate the involvement of IGF-1 in abnormal thyroid growth in Graves' disease, 20 patients with Graves' disease were enrolled in this study. Thirty euthyroid subjects were used as normal controls for the radioimmunoassay study of circulating IGF-1. Seven normal thyroid tissue fragments from 3 patients with papillary carcinoma and 4 patients with benign thyroid nodule were used as controls in the radioligand binding assay. The concentration of serum IGF-1 in the diseased group was not significantly different from normal controls. In the radioligand study, competitive binding studies with thyroid membrane showed that [125I]IGF-1 was dose-dependently displaced by unlabeled IGF-1, and its potency was 630 times higher than insulin. The Scatchard plot of 6 saturation studies revealed similar Kd in the Graves' group and the control group. In contrast, there was a significantly higher specific binding ratio and higher binding capacity in the Graves' group than in the control group. These results suggest that higher IGF-1 receptor numbers rather than higher circulating IGF-1 may be a contributing factor to goiter formation in Graves' disease.