Thyroid-stimulating hormone subunit beta (TSH-B) (Thyrotropin beta chain)
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[edit] Description
Thyrotropin subunit beta precursor (Thyroid-stimulating hormonesubunit beta) (TSH-beta) (TSH-B) (Thyrotropin beta chain). Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland.<ref name="Sacher">Template:Cite book</ref>
[edit] Physiology
[edit] Controlling the rate of release
TSH stimulates the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3).<ref>Template:GeorgiaPhysiology</ref> TSH production is controlled by a Thyrotropin Releasing Hormone, (TRH), which is manufactured in the hypothalamus and transported to the anterior pituitary gland via the superior hypophyseal artery, where it increases TSH production and release. Somatostatin is also produced by the hypothalamus, and has an opposite effect on the pituitary production of TSH, decreasing or inhibiting its release.
The level of thyroid hormones (T3 and T4) in the blood have an effect on the pituitary release of TSH; When the levels of T3 and T4 are low, the production of TSH is increased, and conversely, when levels of T3 and T4 are high, then TSH production is decreased. This effect creates a regulatory negative feedback loop.
[edit] Subunits of TSH
TSH is a glycoprotein and consists of two subunits, the alpha and the beta subunit.
- The α (alpha) subunit (i.e., chorionic gonadotropin alpha) is identical to that of human chorionic gonadotropin (HCG), luteinizing hormone (LH), follicle-stimulating hormone (FSH).
- The β (beta) subunit is unique to TSH, and therefore determines its function.
[edit] The TSH receptor
The TSH receptor is found mainly on thyroid follicular cells<ref>Parmentier M, Libert F, Maenhaut C, et al (December 1989). "Molecular cloning of the thyrotropin receptor". Science (journal) 246 (4937): 1620–2. doi:. PMID 2556796.</ref>. Stimulation of the receptor increases T3 and T4 production and secretion.
Stimulating antibodies to this receptor mimic TSH action and are found in Graves' disease.
[edit] Diagnostic use
TSH levels are tested in the blood of patients suspected of suffering from excess (hyperthyroidism), or deficiency (hypothyroidism) of thyroid hormone. Generally, a normal range for TSH for adults is between 0.4 and 5.0 uIU/mL (equivalent to mIU/L), but values vary slightly among labs. The optimal goal TSH level for patients on treatment ranges between 0.3 to 3.0 mIU/L.<ref>American Association of Clinical Endocrinologists</ref>. The interpretation depends also on what the blood levels of thyroid hormones (T3 and T4) are. The National Health Service in the UK considers a "normal" range to be more like 0.1 to 5.0 uIU/mL.Template:Fact
TSH levels for children normally start out much higher. In 2002, the National Academy of Clinical Biochemistry (NACB) in the United States recommended age-related reference limits starting from about 1.3-19 uIU/mL for normal term infants at birth, dropping to 0.6-10 uIU/mL at 10 weeks old, 0.4-7.0 uIU/mL at 14 months and gradually dropping during childhood and puberty to adult levels, 0.4-4.0 uIU/mL.<ref>Template:Cite web - see Section 2. Pre-analytic factors</ref>
The NACB also stated that it expected the normal (95%) range for adults to be reduced to 0.4-2.5 uIU/mL, because research had shown that adults with an initially measured TSH level of over 2.0 uIU/mL had "an increased odds ratio of developing hypothyroidism over the [following] 20 years, especially if thyroid antibodies were elevated".<ref>Template:Cite web - see Section 3.C.Thyrotropin/ Thyroid Stimulating Hormone (TSH) measurement</ref>
| Source of pathology | TSH level | thyroid hormone level | Disease causing conditions |
| hypothalamus/pituitary | high | high | benign tumor of the pituitary (adenoma) or thyroid hormone resistance |
| hypothalamus/pituitary | low | low | hypopituitarism |
| thyroid | low | high | hyperthyroidism or Grave's disease |
| thyroid | high | low | congenital hypothyroidism (cretinism), hypothyroidism |
Clearly, both TSH and T3 and T4 should be measured to ascertain where a specific thyroid dysfunction is caused by primary pituitary or by a primary thyroid disease. If both are up (or down) then the problem is probably in the pituitary. If the one component (TSH) is up, and the other (T3 and T4) is down, then the disease is probably in the thyroid itself. The same holds for a low TSH, high T3 and T4 finding.
A TSH assay is now also the recommended screening tool for thyroid disease. Recent advances in increasing the sensitivity of the TSH assay make it a better screening tool than free T4.<ref name="Sacher"/>
[edit] Therapeutic use
A drug, recombinant human TSH (rhTSH), called Thyrogen, is manufactured by Genzyme Corp. in Cambridge, Massachusetts. The rhTSH is used in patients with thyroid cancer which is related to tumoral factors.
[edit] Source Organism
Equus caballus (Horse).
[edit] Taxomomy
Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi;Mammalia; Eutheria; Laurasiatheria; Perissodactyla; Equidae; Equus.
[edit] Subcellular Localization
Secreted protein.
[edit] Developmental Stage
[edit] Similarity
Belongs to the glycoprotein hormones subunit beta family.
[edit] Post translational Modification
[edit] Function
Indispensable for the control of thyroid structure and metabolism
[edit] GeneID
100034188
