FIG. 1.

Insulin-like growth factor 1 (IGF-1) has additive to synergistic effects on thyrotropin (TSH) stimulation of thyroid-specific genes, particularly the sodium–iodide symporter (NIS). Human thyrocytes were stimulated with the indicated doses of TSH alone or in combination with 100 ng/mL of IGF-1. RNA was isolated after 48 h, cDNA synthesized, and the indicated genes measured by quantitative polymerase chain reaction (PCR). Data are expressed as the mean ± standard error of the mean (SEM), n = 6. ***p < 0.001, ****p < 0.0001, TSH + IGF-1 versus TSH alone curve for thyroglobulin (TG), thyroperoxidase (TPO), and deiodinase type 2 (DIO2), at indicated doses for NIS.