Type 1 and type 2 iodothyronine deiodinases in the thyroid gland of patients with huge goitrous Hashimoto’s thyroiditis
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The serum free triiodothyronine (FT3)/free thyroxine (FT4) ratio in patients with huge goitrous Hashimoto’s thyroiditis (HG-HT) is relatively high. We investigated the cause of high FT3/FT4 ratios.
We measured the serum FT3, FT4, and thyrotropin (TSH) levels of seven patients with HG-HT who had undergone a total thyroidectomy. Eleven patients with papillary thyroid carcinoma served as controls. The activities and mRNA levels of type 1 and type 2 iodothyronine deiodinases (D1 and D2, respectively) were measured in the thyroid tissues of HG-HT and perinodular thyroid tissues of papillary thyroid carcinoma.
The TSH levels in the HG-HT group were not significantly different from those of the controls. The FT4 levels in the HG-HT group were significantly lower than those of the controls, whereas the FT3 levels and FT3/FT4 ratios were significantly higher in the HG-HT group. The FT3/FT4 ratios in the HG-HT group who had undergone total thyroidectomy and received levothyroxine therapy decreased significantly to normal values. Both the D1 and D2 activities in the thyroid tissues of the HG-HT patients were significantly higher than those of the controls. However, the mRNA levels of both D1 and D2 in the HG-HT patients’ thyroid tissues were comparable to those of the controls. Interestingly, there were significant correlations between the HG-HT patients’ D1 and D2 activities, and their thyroid gland volume or their FT3/FT4 ratios.
Our results indicate that increased thyroidal D1 and D2 activities may be responsible for the higher serum FT3/FT4 ratio in patients with HG-HT.
KeywordsThyroid hormone metabolism Iodothyronine deiodinase Hashimoto’s thyroiditis Thyroid gland
This study was supported by the Smoking Research Foundation of Japan Grant Number FP01606073.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This study was approved by the Ethics Committee at Kuma Hospital, and all patients gave informed consent for their materials to be used and for their data to be published. This study was conducted in accordance with the principles of the Declaration of Helsinki.
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