The Effects of Radiographic Contrast Agents and Other Compounds on the Nuclear Binding of L-[125I]Triiodothyronine in Dispersed Human Skin Fibroblasts*

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Abstract
Using a dispersed intact cell assay system, we screened a number of compounds for their ability to compete for nuclear binding of L-[125I]T3 in cultured human skin fibroblasts incubated for 90 min at 37 °C. T3 inhibited nuclear [125I]T3 binding by 50% at a concentration of 3.4 ± 0.3 (±SE) × 10-10 M. 3,5-Dimethyl-3′-isopropyl-thyronine, a nonhalogenated thyroid hormone agonist, had an affinity for the nuclear thyroid hormone receptor (4.4 × 10-9 M, as judged by 50% inhibition of nuclear [125I]T3 binding) that correlates well with its thyromimetic potency. Of several radiographic contrast agents and other compounds tested (iodipamide, iopanoic acid, sodium ipodate, sodium diatrizoate, sodium tyropanoate, diphenylhydantoin, carbamazepine, amiodarone hydrochloride, propylthiouracil, propranolol, and potassium iodide), only sodium ipodate (Oragrafin) and iopanoic acid (Telepaque) interfered with nuclear [125I]T3 binding, with 50% inhibition at 5 × 10-6 and 1.8 × 10-4 M, respectively. Interestingly, diphenylhydantoin and amiodarone, two compounds previously thought to interact with thyroid hormone receptors, did not impair fibroblast nuclear [126I]T3 binding at concentrations up to 10-3 M. We conclude that this in vitro assay system with intact human cells is useful in evaluating the nuclear T3 receptor affinity of compounds that affect thyroid hormone action or metabolism. These studies more closely approximate in vivo conditions and, therefore, provide information not obtainable by studies with isolated nuclei or nuclear extracts. (J Clin Endocrinol Metab60: 548, 1985)

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