Thyroxine Information
Thyroxine, or 3,5,3',5'-tetraiodothyronine (often abbreviated as T4),a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.
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Synthesis and regulation
The system of the thyroid hormones T3 and T4.[3] Further information: Thyroid hormoneThyroxine is synthesized via the iodination and covalent bonding of the phenyl portions of tyrosine residues found in an initial peptide, thyroglobulin, which is secreted into thyroid granules. These iodinated diphenyl compounds are cleaved from their peptide backbone upon being stimulated by thyroid-stimulating hormone.
Transport
T4 is transported in blood, with 99.95% of the secreted T4 being protein-bound, principally to thyroxine-binding globulin (TBG), and, to a lesser extent, to transthyretin and serum albumin. The half-life of thyroxine once released into the blood circulatory system is about 1 week.
Effects
Further information: Thyroid hormoneT4 is involved in controlling the rate of metabolic processes in the body and influencing physical development. Administration of thyroxine has been shown to significantly increase the concentration of nerve growth factor in the brains of adult mice.[4]
Thyroxine is a prohormone and a reservoir for the active thyroid hormone triiodothyronine (T3), which is about four times more potent. T4 is converted in the tissues by deiodinases, including thyroid hormone iodine peroxidase (TPO), to T3. The "D" isomer is called "Dextrothyroxine"[5] and is used as a lipid modifying agent.[6]
History
Thyroxine was first isolated in pure form in 1914 at the Mayo Clinic by Edward Calvin Kendall from extracts of hog thyroid glands.[7] The hormone was synthesised in 1927 by British chemists Charles Robert Harington and George Barger.
Measurement
Further information: Thyroid function testsThyroxine can be measured as free thyroxine, which is an indicator of thyroxine activity in the body. It can also be measured as total thyroxine, which also depends on the thyroxine that is bound to thyroxine-binding globulin. A related parameter is the free thyroxine index, which is total thyroxine multiplied by thyroid hormone uptake, which, in turn, is a measure of the unbound thyroxine binding globulins.[8]
The normal human adult range of T4 in blood is 4 - 11 mcg/dL
See also
Reactions
- Transformations
References
- ^ Harington in: Biochem. J. 1926, 20, 310.
- ^ Thyroxine in the ChemIDplus database
- ^ References used in image are found in image article in Commons: References.
- ^ Walker et al. (27 April 1979) Thyroxine increases nerve growth factor concentration in adult mouse brain. Science. Vol. 204, No. 4391. pp. 427 - 429.
- ^ MeSH Dextrothyroxine
- ^ C10 AX01
- ^ E.C. Kendall in J. Am. Med. Assoc., 1915, Vol. 64, pp 2042-2043: The isolation in crystalline form of the compound containing iodin, which occurs in the thyroid: Its chemical nature and physiologic activity.
- ^ Military Obstetrics & Gynecology > Thyroid Function Tests In turn citing: Operational Medicine 2001, Health Care in Military Settings, NAVMED P-5139, May 1, 2001, Bureau of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington, D.C., 20372-5300
Categories: Hormones of the thyroid gland | Hormones of the hypothalamus-pituitary-thyroid axis | Iodinated tyrosine derivatives | Halogen-containing natural products | Thyroid hormones | Aromatic compounds
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