THE IN VITRO METABOLISM OF THYROXINE, TRIIODOTHYRONINE AND THEIR ACETIC AND PROPIONIC ACID ANALOGUES1

Publisher Website
Google Scholar
Abstract
The metabolism of thyroxine, triiodothyronine and their acetic and propionic acid analogues has been studied by placing these I131 labelled substrates in buffered medium with or without added tissue. Spleen, kidney and liver slices, homogenates and fractions of homogenates were used. Samples of medium and/or homogenized slices, usually after three hours incubation at 37[degree]C, were chromatographed and quantitated by strip counting. The only product of deiodination detected was iodide. When thyroxine endogenously labelled with I131 was used, no 3,5-diiodothyronine or other partially deiodinated thyronines or derivatives were formed, although activity was low and small amounts of other products could not be ruled out. Deiodination was inhibited by a nitrogen atmosphere, boiling, heavy metals, cyanide, 2 methyl 1,4-naphthoquinone, a chelating agent (Versene), and estrogenic substances. No antithyroid substances, including iodide and propylthiouracil, had any effect; iodinated tyrosines and organic iodine compounds had no effect. All tetra and tri iodinated thyronines inhibited the deiodination of other tetra and tri iodinated thyronines often commensurate with the degree of their own deiodination. Only one iodinated compound, other than these, was an effective inhibitor: N-butyl para hydroxy diiodo-benzoate.