Type 1 iodothyronine
deiodinase in human physiology and disease.
Due to structural resemblance of human chorionic gonadotropin (hCG) with TSH, hCG stimulates thyroid gland, resulting in an increase in its secretion of tetra-iodothyronine (T4) and tri-iodothyronine (T3) during the early phase of pregnancy followed by a plateauing at approximately 16 weeks of gestation.6 Thyroid hormone is degraded by placental type 3 iodothyronine
deiodinase, necessitating increased production of maternal thyroid hormone.4
"Selenium is also an integral part of the enzyme Typel iodothyronine
deiodinase, which catalyzes the deiodination of the iodothyronines
, notably the deiodination of thyroxine (T4) to triiodothyronine (T3), the most active of the thyroid hormones.
Type 2 iodothyronine
deiodinase (Dio2) is responsible for local T4 to T3 conversion and is regulated by adrenergic stimulation (15).
Hepatocyte nuclear factor 4a contributes to thyroid hormone homeostasis by cooperatively regulating the type 1 iodothyronine
deiodinase gene with GATA4 and Kruppellike transcription factor 9.
It is a constituent of the main selenoproteins expressed by the gland, such as glutathione peroxidase (GPX), thioredoxin reductase (TR) and iodothyronine
desiodinases (DIO), responsible for the processes of elimination of hydrogen peroxide ([H.sub.2][O.sub.2]) and deiodination.
Ligand-induced inactivation of type I iodothyronine
5'-deiodinase: protection by propylthiouracil in vivo and reversibility in vitro.
There are several types of iodothyronine
deiodinases, including two activating enzymes (D1 and D2) and one inactivating enzyme (D3).
Type II iodothyronine
deiodinase (D2) is encoded by the gene DIO2 whose major function is to enzymatically convert thyronine (T4) to T3 .
Some forms of gastrointestinal GSH-Px, plasma GSH-Px kinase, and iodothyronine
deiodinases are synthesized and activated when the Se level in a diet is optimal [2, 3, 6-8].
 where the author observed an increased expression of type 2 iodothyronine
deiodinase in human osteoblasts which was stimulated by thyrotropin (TSH).
A subclinical hypothyroidism diagnosis was established in the presence of normal FT4 and high TSH values, an overt hypothyroidism diagnosis in the presence of low FT4 and high TSH, and hyperthyroidism diagnosis with high FT4 and/or high free iodothyronine
(FT3) and low TSH.