The L-triiodothyronine (T3, liothyronine) thyroid hormone is normally synthesized and secreted by the thyroid gland in much smaller quantities than L-tetraiodothyronine (T4, levothyroxine, L-thyroxine). Most T3 is derived from peripheral monodeiodination of T4 at the 5 position of the outer ring of the iodothyronine nucleus. The hormone finally delivered and used by the tissues is mainly T3. [PubChem]
Used as replacement or supplemental therapy in patients with hypothyroidism of any etiology, except transient hypothyrodism during the recovery phase of subacute thyroiditis.
Thyroid hormone drugs are natural or synthetic preparations containing T<sub>4</sub> or T<sub>3</sub> or both. T<sub>4</sub> and T<sub>3</sub> are produced in the human thyroid gland by the iodination and coupling of the amino acid tyrosine. Liothyronine (T<sub>3</sub>) contains three atoms of iodine and is formed by the coupling of one molecule of diiodotyrosine (DIT) with one molecule of monoiodotyrosine (MIT). These hormones enhance oxygen consumption by most tissues of the body and increase the basal metabolic rate and the metabolism of carbohydrates, lipids and proteins. Thus, they exert a profound influence on every organ system in the body and are of particular importance in the development of the central nervous system.
Mechanism of action
The hormones, T<sub>4</sub> and T<sub>3</sub>, are tyrosine-based hormones produced by the thyroid gland. Iodine is an important component in their synthesis. The major form of thyroid hormone in the blood is thyroxine (T4). This is converted to the more active liothyronine form by deiodinases in peripheral tissues. Liothyronine acts on the body to increase the basal metabolic rate, affect protein synthesis and increase the body's sensitivity to catecholamines (such as adrenaline). The thyroid hormones are essential to proper development and differentiation of all cells of the human body. To various extents T<sub>4</sub> and T<sub>3</sub> regulate protein, fat and carbohydrate metabolism. Their most pronounced effect is on how human cells use energetic compounds. The thyroid hormone derivatives bind to the thyroid hormone receptors initially to initiate their downstream effects.
Route of administration
Amino Acids, Aromatic
Amino Acids, Cyclic
Amino Acids, Peptides, and Proteins
Chemical Actions and Uses
Hormones, Hormone Substitutes, and Hormone Antagonists
Physiological Effects of Drugs
Systemic Hormonal Preparations, Excl. Sex Hormones and Insulins
Drug Info/Drug Targets: DrugBank 3.0: a comprehensive resource for 'omics' research on drugs. Knox C, Law V, Jewison
T, Liu P, Ly S, Frolkis A, Pon A, Banco K, Mak C, Neveu V, Djoumbou Y, Eisner R, Guo AC, Wishart DS.
Nucleic Acids Res. 2011 Jan; 39 (Database issue):D1035-41. | PMID:21059682