The biological action of substances related to thyroxine. 8. The effects of butyl 4-hydroxy-3:5-diiodobenzoate on the deiodination of diiodotyrosine and thyroxine in rats

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Abstract
An electro-metric method for detn. of small amts. of iodide in rat urine in the presence of relatively large quantities of organically combined I was studied. With a silver: silver sulfide electrode the method can be applied to detn. of about 20[mu]g. of iodide in the presence of 1.5 mg. organic I in 50 ml. urine. A method developed for separation of thyronine derivatives from solns. containing iodide was used to confirm that the urinary radioactivity after treatment with thyroxine labelled in the 3[image],5[image] positions with I131 was due to iodide. Solns. of radio-thyroxine in 0.02 [image] Na carbonate undergo considerable decomposition on storage. After 3 wks. about 6% of the radioactivity was due to iodide. The urinary iodide after injn. of diodotyrosine or thyroxine was markedly reduced by the simultaneous admn. of butyl 4-hydroxy-3,5-diiodobenzoate. These results support the hypothesis that butyl 4-hydroxy-3,5-diiodobenzoate interferes with conversion of thyroxine into triiodothyronine.