Effect of Butyl-4-hydroxy-3,5-diiodobenzoate on the Metabolism of L-Thyroxine and Related Compounds

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Abstract
Butyl hydroxydiiodobenzoate (BHDB) has been fed to rats within a few hours of the time of injection of L-thyroxine, L-3,5,3′-triiodothyronine, tetraiodothyroacetic acid, 3,5,3′-triiodothyroacetic acid, tetraiodothyropropionic acid and 3,5,3′-triiodothyropropionic acid, all of which were labeled with 131I in the 3′ or 5′ position. BHDB greatly stimulated conjugation of these substances and their metabolites and greatly increased the excretion of these conjugates in the bile. BHDB also inhibited deiodination of the thyroid hormones and analogs from the 3′ or 5′ position and thus decreased excretion of radioactive iodide in the urine. The stimulatory effect of BHDB on conjugation was much greater than its inhibitory effect on deiodination but did not persist as long. BHDB, which has been shown to alter the binding of thyroxine to plasma proteins, probably improves the transport of the thyroid hormones and analogs to the sites in the cell where the enzyme systems for conjugation are located. The stimulation of conjugation by BHDB was greatest for tetraiodothyroacetic acid, which was conjugated in smallest amounts by untreated rats, and the stimulation was the least for triiodothyroacetic and triiodothyropropionic acids, which were conjugated in largest amounts by untreated rats. The pattern of conjugates excreted in the bile by BHDB-treated rats was essentially the same as in untreated rats except for some shifts in the relative amounts of the glucuronides and sulfates of thyroxine and triiodothyronine and their metabolites. (Endocrinology75: 721, 1964)