MCT8 is Downregulated by Short Time Iodine Overload in the Thyroid Gland of Rats

An interesting abstract which suggests a possible explanation of the Wolff-Chaikoff effect.

Horm Metab Res. 2015 May 28. [Epub ahead of print]

MCT8 is Downregulated by Short Time Iodine Overload in the Thyroid Gland of Rats.

de Souza EC1, Dias GR1, Cardoso RC1, Lima LP1, Fortunato RS1, Visser TJ2, Vaisman M3, Ferreira AC1, Carvalho DP1.

Author information

1 Laboratory of Endocrine Physiology Doris Rosenthal, Institute of Biophysics Carlos Chagas Filho, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.

2 Department of Internal Medicine, Erasmus University Medical Center, Rotterdam, The Netherlands.

3 Universitary Hospital Clementino Fraga Filho, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.

Abstract

Wolff-Chaikoff effect is characterized by the blockade of thyroid hormone synthesis and secretion due to iodine overload. However, the regulation of monocarboxylate transporter 8 during Wolff-Chaikoff effect and its possible role in the rapid reduction of T4 secretion by the thyroid gland remains unclear. Patients with monocarboxylate transporter 8 gene loss-of-function mutations and monocarboxylate transporter 8 knockout mice were shown to have decreased serum T4 levels, indicating that monocarboxylate transporter 8 could be involved in the secretion of thyroid hormones from the thyroid gland. Herein, we aimed to evaluate the regulation of monocarboxylate transporter 8 during the Wolff-Chaikoff effect and the escape from iodine overload, besides the importance of iodine organification for this regulation. Monocarboxylate transporter 8 mRNA and protein levels significantly decreased after 1 day of NaI administration to rats, together with decreased serum T4; while no alteration was observed in LAT2 expression. Moreover, both monocarboxylate transporter 8 expression and serum T4 was restored after 6 days of NaI. The inhibition of thyroperoxidase activity by methimazole prevented the inhibitory effect of NaI on thyroid monocarboxylate transporter 8 expression, suggesting that an active thyroperoxidase is necessary for MCT8 downregulation by iodine overload, similarly to other thyroid markers, such as sodium iodide symporter. Therefore, we conclude that thyroid monocarboxylate transporter 8 expression is downregulated during iodine overload and that the normalization of its expression parallels the escape phenomenon. These data suggest a possible role for monocarboxylate transporter 8 in the changes of thyroid hormones secretion during the Wolff-Chaikoff effect and escape.

© Georg Thieme Verlag KG Stuttgart · New York.

PMID: 26021458 [PubMed - as supplied by publisher]

ncbi.nlm.nih.gov/pubmed/260...

Articles about thyroid hormone transporters such as MCT8:

ncbi.nlm.nih.gov/pmc/articl...

and

thyroidmanager.org/chapter/...

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  • Thanks, Helvella.

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