T4Hormon

T4Hormon, commonly known as thyroxine, is one of the primary thyroid hormones produced by the thyroid gland. It contains four iodine atoms and serves as a prohormone for the more active triiodothyronine (T3).

Typically secreted into the bloodstream in larger amounts than T3, T4 is relatively less active but serves as a circulating reservoir. In peripheral tissues, enzymes called deiodinases remove iodine to convert T4 into T3, the form that binds most strongly to thyroid hormone receptors.

Thyroxine exerts effects by entering cells, binding to nuclear thyroid hormone receptors (TRα and TRβ), and altering transcription of target genes. This regulates basal metabolic rate, heat generation, protein synthesis, carbohydrate and lipid metabolism, and is essential for normal growth and brain development, especially in prenatal and early postnatal life.

In medicine, levothyroxine is a widely used synthetic form of T4 for treating hypothyroidism and certain thyroid cancers. Dosing is individualized and monitored by measurements of thyroid-stimulating hormone (TSH) and free thyroxine (free T4).

Chemically, thyroxine is an iodinated amino acid-derived compound called tetraiodothyronine. Its pharmacokinetics, including half-life and tissue distribution, are influenced by nutritional status and concurrent medications.