A Probable Abnormality in Intrathyroidal Iodine Metabolism in Hyperthyroidism1

Publisher Website
Google Scholar
Abstract
Euthyroid and hyperthyroid patients were given radioiodine. Measurements were made of thyroid uptake, urinary radioiodine excretion, serum protein-bound radioiodine concentration and body radioactivity for from 5 to 15 days before and for from 7 to 15 days after Tapazole was started. Stable serum protein-bound iodine concentration and urinary iodine excretion were determined. After Tapazole administration the urinary excretion of radioiodine increased above the amount predicted from a block of the uptake of recycling extrathyroidal hormonal radioiodine in euthyroid patients but equaled the predicted increase in hyperthyroid patients. An effect of Tapazole on the peripheral metabolism of thyroxine was not demonstrated clearly, nor would it probably have accounted for the difference noted. Iodide therapy resulted in a striking diminution in urinary radioiodine excretion in one patient receiving Tapazole, with a concomitant slowing in the decrease of thyroidal radioiodine without a reciprocal effect on the serum protein-bound radioiodine concentration. A theoretic explanation is offered for these observations: that the hyperthyroid gland normally secretes large quantities of non-thyroxine iodine, possibly in the form of iodide, and that iodide therapy may reduce this secretion without affecting the release of thyroxine iodine.