Roentgenographic Contrast Agents Inhibit Triiodothyronine Binding to Nuclear Receptors in Vitro*

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Abstract
The ability of roentgenographic contrast agents to inhibit binding of [125I]T3 to nuclear receptors was studied during incubation of rat liver nuclei or nuclear extracts in vitro and after ip administration of the agents in vivo. Ipodate, iodipamide, iopanoic acid, and diatrizoate inhibited binding of [l25I]T3 in vitro. The most potent inhibitor was ipodate, which produced 50‰ inhibition of binding at 1.2 X 104 M. When given orally in acute in vivo experiments, ipodate did not diminish binding to liver nuclear receptors. Ipodate appeared to inhibit in vivo metabolism of [125I]T3.