Regulation of receptors for insulin-like growth factors in cultured arterial smooth muscle cells by thyroid hormone.

The effect of tri-iodothyronine (T3) on the binding of 125I-labelled insulin-like growth factors (IGF) to cultured arterial smooth muscle cells was investigated. When cells which were grown to confluency were incubated with 125I-labelled IGF and different concentrations of T3, low concentrations of T3 (0.1-10 nmol/l) increased the binding of 125I-labelled IGF. High concentrations of T3 (1 mumol/l) could not induce this effect. Scatchard analysis of the binding of 125I-labelled IGF in the presence of different concentrations of unlabelled IGF showed a high-affinity, low-capacity binding system and a second lower affinity, high-capacity binding system. In the presence of T3 (1 nmol/l) Scatchard analysis indicated that the affinity of 125I-labelled IGF to its binding sites was altered. After a 2-h preincubation of the cell layers with Dulbecco's Modified Eagle's Medium containing T3 (1-100 nmol/l), the 125I-labelled IGF binding was enhanced in a dose-dependent manner by T3. Scatchard analysis showed a significant increase in the number of IGF binding sites.