Effect of Methimazole Upon Thyroid Clearance of Circulating Iodide

Thyroid radioiodide to serum radioiodide concentration (*T/*S) ratios 1 h after 131I administration were 3 times higher in rats pretreated with propylthiouracil (PTU) than in rats with binding thyroids. Although indications of a preponderance of transported iodide in the thyroid early after 131I injection were found, a reduction of the 1-h *T/*S ratio in TSH-treated rats by the inhibitor of iodotyrosine dehalogenation, mononitrotyrosine, points to an early contribution of intrathyroidally generated (internal) iodide to total thyroid iodide. In rat thyroids labeled 72 h earlier, there was no rise in electrophoretically separated radioiodide 2 h after the administration of PTU alone, but the elevation of thyroid iodide due to TSH was augmented by concurrently given PTU. On the assumption that PTU affects transported components of thyroid iodide identically whether they are labeled 1 or 72 h earlier, we conclude that PTU must severely depress the generation of internal iodide. This effect is no longer evident if TSH is given simultaneously. Further, our results are consistent with the hypothesis that internal iodide passes through a stage in which it is not available for organic binding before it mixes with transported iodide. TSH appears to facilitate the transfer of internal iodide into the pool which it shares with external iodide.

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Intrathyroidally Generated Iodide: The Role of Propylthiouracil-Sensitive Processes in Its Production*

Hildebrandt

Halmi

1980

Endocrinology

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Preservation of Sodium-Dependent Iodide Transport Activity By Methimazole and Mercaptoethanol in Phospholipid Vesicles Containing Thyroid Plasma Membranes: with Evidence of Difference in the Action of Perchlorate and Thiocyanate.

Saito¹,

Yamamoto²,

Nagayama³

et al. 1989

Endocrinol Japon

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The effect of methimazole (MMI) and 2-mercaptoethanol (ME) on I-transport was studied using phospholipid vesicles (P-vesicles) made from porcine thyroid plasma membranes and soybean phospholipids by sonication. 1. When buffer solutions contained either 1 mM MMI or 2 mM ME, I-uptake by P-vesicles in the presence of external Na+ was apparently higher than that in the absence of external Na+. Na+-dependent I- uptake was inhibited by both C1O4- and SCN- added externally. 2. When PM was treated with 4 mM N-ethylmaleimide prior to preparation of P-vesicles, the activity of Na+-dependent I- transport was completely lost even when P-vesicles were incubated in the presence of ME. 3. When neither MMI nor ME was added to buffers, I- uptake in the presence of external Na+ was not at all higher than that in the absence of external Na+. In these instances, however, I- uptake was much higher compared than the baseline uptake in the presence of MMI or ME, and was inhibited by external SCN- and not by C1O4- without relation to external Na+. These data indicate that MMI or ME has two distinct effects on our model system of I- transport. The one is preservation of the Na+-dependent I- transport activity by protecting a sulfhydryl group, and the other is reduction of nonspecific I- binding to P-vesicles. In addition, C1O4- is a more specific inhibitor of thyroid I- transport than SCN-, when non-specific I- oxidation is imperfectly prevented.

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Effect of Methimazole Upon Thyroid Clearance of Circulating Iodide

Cited by 2 publications

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Intrathyroidally Generated Iodide: The Role of Propylthiouracil-Sensitive Processes in Its Production*

Intrathyroidally Generated Iodide: The Role of Propylthiouracil-Sensitive Processes in Its Production*

Preservation of Sodium-Dependent Iodide Transport Activity By Methimazole and Mercaptoethanol in Phospholipid Vesicles Containing Thyroid Plasma Membranes: with Evidence of Difference in the Action of Perchlorate and Thiocyanate.

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