Thyroid stimulating hormone, Triiodothyronine and Thyroxine (TSH, T3 and T4)

Thyroid stimulating hormone (TSH) is secreted by the anterior pituitary gland and plays an important role in promoting thyroid hormone synthesis and release. As a specific biomarker for hyperthyroidism and hypothyroidism, TSH contains 211 amino acids, of which about 15% are sugars, and consists of two peptide chains, A and B. TSH is also known to be the most important peptide in the thyroid function.

Triiodothyronine (T3) hormone is also associated with the thyroid gland, about 65% of which is secreted directly by the thyroid gland, while the remaining 35% is formed by deiodination of T4 in peripheral tissues, and has a molecular weight of about 650, making it a semi-antigenic, small molecule substance. Triiodothyronine is involved in every physiological process in the body, including growth and development, metabolism, regulation of body temperature and heart rate.

Thyroxine (T4) is a kinin synthesized by the thyroid follicles, with a molecular weight of 777 Da, and its secretion is mainly regulated by the hypothalamic-pituitary-thyroid axis. Under the stimulation of pituitary thyroid stimulating hormone, thyroglobulin hydrolyzes and releases T4 into the bloodstream. 99.97% of the T4 in the bloodstream is bound to thyroid-binding globulin or thyroid-binding preprotein, and 0.03% exists in the free state. The sum of the thyroxine present in the free state (FT4) and the thyroxine present in the non-free state is called total thyroxine (TT4).

KMD Bioscience, as a supplier of in vitro diagnostic raw materials, provides the IVD industry with high-quality diagnostic antigens and antibody raw materials for flow, colloidal gold, chemiluminescence, immunoturbidimetric, and other assay platforms for over several years. KMD Bioscience's antibody diagnostic raw materials and antigen diagnostic raw materials are strictly monitored during the R&D and production phases, and the performance indicators (specificity, activity, stability, etc.) of antibodies/antigens are analyzed to ensure that IVD raw materials are characterized by small batch-to-batch/intra-batch variations, wide linear ranges, good stability, high sensitivity, and so on.

The inventory of reagents associated with TSH, T3, T4 that KMD Bioscience can offer:

TSH and antibody-mediated TSHR activation

When the body is stimulated, the hypothalamus releases thyrotropin-releasing hormone (TRH), which in turn stimulates the pituitary gland to release TSH, which activates the G-protein-coupled thyroid stimulating hormone receptor (TSHR) expressed on thyroid cells to regulate thyroid hormone synthesis.

TSH is a member of a family of glycoprotein hormones that also includes follicle stimulating hormone (FSH), luteinizing hormone (LH), and chorionic gonadotropin (CG).2 The TSHR and related glycoprotein hormone receptors contain leucine repeat structural domains (LRRDs), hinge regions, and transmembrane structural domains (TMDs). Among other things, the TSHR α-subunit can dissociate from the β-subunit and become an antigen, which is further recognized by the immune system and produces autoantibodies. Autoantibodies that activate TSHR, including M22, increase the abnormal secretion of thyroid hormones and lead to Graves' disease and orbital disease; autoantibodies that inhibit TSHR, such as K1-70, inhibit the secretion of thyroid hormones and lead to hypothyroidism.

Biological Functions of TSH and T3 and T4

Thyroid stimulating hormone (TSH) plays an important role in the proliferation and growth of thyroid cells. In addition, TSH is involved in the blood supply to the thyroid gland as well as in the synthesis and secretion of thyroid hormones, and plays an important role in maintaining the body's thyroid function.

Triiodothyronine (T3) stabilizes the level of thyroid hormones in the blood. About 99.7% of triiodothyronine (T3) is specifically bound to thyroid hormone binding protein (TBG) in the body, while the remaining 0.3% exists in a free form. Only free T3 (FT3) has metabolic activity, which can reflect the functional state of the thyroid gland and other effects on human function more accurately, and the sum of the free T3 and the bound state is called total T3 (TT3). after the production of T3 is activated by thyroid-stimulating hormone (TSH), T3 is released into the bloodstream, and the elevated plasma concentration of T3 inhibits the production of anterior pituitary thyroid hormone (TSH), and then the concentration of T3 decreases. The increased plasma concentration of T3 inhibits the production of thyroid hormone (TSH), followed by a decrease in the concentration of T3 and an increase in the release of TSH from the anterior pituitary gland.T3 stabilizes the level of thyroid hormones in the bloodstream through this feedback regulation.

Thyroxine (T4) is the main product secreted by the thyroid gland and is used in the diagnosis of hyperthyroidism, primary and secondary hypothyroidism, and in TSH suppression therapy.

Relationship between TSH and T3 and T4

Thyroid-stimulating hormone (TSH) plays a comprehensive role in promoting the function of the thyroid gland. Before, TSH promotes the release of thyroid hormones, and after, it promotes the synthesis of T4 and T3, which is manifested in the enhancement of the iodine pump activity, the enhancement of the activity of peroxidase, and the promotion of the synthesis of thyroglobulin and iodination of tyrosine acid. The results show that: TSH can promote the metabolism of epithelial cells, and can cause the production of nucleic acids and proteins in epithelial cells, and can cause the high proliferation of epithelial cells, which in turn can cause the size of the gland to increase. The pituitary gland secretes TSH, which is stimulated by thyrotropin-releasing hormone (TRH) secreted by the hypothalamus and, on the other hand, is inhibited by feedback from T3 and T4, which can antagonize each other. These cells constitute the "hypothalamic-pituitary-thyroid" center. Normally, the feedback regulation of the pituitary-thyroid axis is determined by the amount of TRH secreted by the hypothalamus; the more TRH is secreted, the higher the regulation point of T3 and T4 in the blood, and if the regulation value of T3 and T4 exceeds this value, it will feedback inhibit the secretion of TSH, reduce its sensitivity to TRH, and maintain the level of T3 and T4 in the blood at a relatively stable level. External stimuli such as hypothermia secrete TRH through the hypothalamus, which, through the adeno-pituitary axis, increases the concentration of T3 and T4 in the blood. Therefore, T3 and T4 should be combined with ultrasensitive TSH as the preferred method of thyroid function tests.

Figure 1 Relationship between TSH, T3, and T4

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