Iopanoic acid

Iopanoic acid is an inhibitor of 5'-Deiodinase and also an iodinated contrast medium. IC50 & Target: 5'-Deiodinase^[1] In Vitro: The thyrotropin-releasing-hormone (TRH)-induced thyrotropin (TSH) release from the pituitary fragments is inhibited by 3,5,3'-triiodothyronin (T₃) (10^-7 M), by triiodothyroacetic acid (10^-7 to 10^-7 M), and by high concentrations of iodide (10^-4 or 10^-5 M). Iopanoic acid has no significant effect at the concentrations tested^[2]. In Vivo: Iopanoic acid (IOP) administration to pregnant rats during days 18 and 19 postconception does not modify litter size (controls: 11.8±0.5 fetusesldam, Iopanoic acid-treated: 11.6±0.6 fetusesldam) or body weight at day 20 (controls: 3.27±0.12 g, Iopanoic acid-treated: 3.42±0.20 g). Iopanoic acid treatment produces a significant blockage of 5'-Deiodinase (5'D) activity in interscapular brown adipose tissue (IBAT) and brain; in contrast, liver 5'D is not modified. 3,5,3'-triiodothyronin (T₃) content is similar in IBAT and slightly increased in brain and liver nuclei of Iopanoic acid-treated fetuses when compare with control fetuses at day 20 (p<0.05). However, when administered to adult rats, Iopanoic acid produces a significant reduction in IBAT nuclear T₃ content and plasma T₃ concentration. Iopanoic acid inhibition of IBAT 5'D activity in fetuses at term is as effective as at day 20^[1].