On the Nature of Iodine Released by Thyroid Slices

Rabbits were given relabeled iodide of constant specific activity by daily injections or in the diet for varying lengths of time. Even after 24 days’ administration, only 75% of the expected equilibrium value was attained in thyroidal iodine. Thyroid slices from these rabbits were incubated and the media therefrom were examined by trichloroacetic acid (TCA) precipitation, chromatography and electrophoresis. About 40–60% of the radioiodine in the slices was released into the medium in 90 min. Of this, about 2 % was TCA-soluble, and, of the soluble iodine, 10–25% was iodide. The TCAsoluble iodine that was not iodide seemed to be partly in the form of peptides. A mathematical analysis is presented which shows that almost all the iodide released by an incubated slice came from a pool other than one usually described by the T/M value