Decrease in the thyroid internal iodide pool induced by 3-nitro-L-tyrosine (MNT), an inhibitor of iodotyrosine deiodination.

Abstract

Studies have been performed to evaluate further the postulate that the thyroid contains as a distinct functional entity an “internal” or “second” thyroidal iodide pool, arising from intrathyroidal deiodinations, in addition to an iodide pool, representing iodide transported in the thyroid from the extracellular fluid. Thyroidal iodine metabolism was determined after administration of nitro—L—tyrosine (MNT), a potent inhibitor of the deiodination of iodotyrosines. MNT, given acutely to rats, resulted in a significant decrease in the measured iodide content of the internal iodide pool and the internal thyroid/serum iodide concentration ratio, without changing significantly the thyroidal organic iodine content, the iodide content of the external iodide pool or the external thyroid/serum iodide concentration ratio. These results provide additional evidence that the measured internal iodide pool does not represent iodide derived artifactually during analysis, but is indeed a distinct physiological e...