Description
Introduction: Thyroxine, or 3,5,3',5'-tetra-iodothyronine (often abbreviated as T4), a form of thyroid hormones is the major hormone secreted by the follicular cells of the thyroid gland. Thyroxine 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. More in the T3 and T4 section of thyroid. 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. T4 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. Thyroxine is a prohormone and a reservoir for the active thyroid hormone triiodothyronine (T3) which is about four times more 3 potent. T4 is converted in the tissues by deiodinases, including thyroid hormone iodine peroxidase (TPO), to T3. The "D" isomer is called "Dextrothyroxine" and is used as a lipid modifying agent. The half-life of thyroxine once released into the blood circulatory system is about 1 week.
Principle of the Assay: This assay employs the competitive inhibition enzyme immunoassay technique. A antibody specific to T4 has been pre-coated onto a microplate. Standards or samples are added to the appropriate microtiter plate wells with biotin-conjugated T4 and incubated. A competitive inhibition reaction is launched between T4 (Standards or samples) and Biotin-conjugated T4 with the pre-coated antibody specific for T4. The more amount of T4 in samples, the less antibody bound by Biotin-conjugated T4. Then Avidin conjugated to Horseradish Peroxidase (HRP) is added to each microplate well and incubated. The substrate solutions are added to the wells, respectively. And the color develops in opposite to the amount of T4 in the sample. The color development is stopped and the intensity of the color is measured