Reverse triiodothyronine

{{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 441431793 | ImageFile = Reverse triiodothyronine.svg | ImageSize = 230px | ImageAlt = Skeletal formula of reverse triiodothyronine | ImageFile1 = Reverse triiodothyronine zwitterion 3D ball.png | ImageSize1 = 230px | ImageAlt1 = Ball-and-stick model of the reverse triiodothyronine molecule as a zwitterion | IUPACName = ''O''-(4-Hydroxy-3,5-diiodophenyl)-3-iodo-<small>L</small>-tyrosine | SystematicName = (2''S'')-2-Amino-3-[4-(4-hydroxy-3,5-diiodophenoxy)-3-iodophenyl]propanoic acid | OtherNames = reverse triiodothyronine<br />reverse T₃<br />rT₃<br />3,3′,5′-triiodothyronine |Section1={{Chembox Identifiers | IUPHAR_ligand = 2636 | CASNo_Ref = {{cascite|correct|??}} | CASNo = 5817-39-0 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = 8NZ4Y08T96 | PubChem = 22069 | SMILES = C1=CC(=C(C=C1C[C@@H](C(=O)O)N)I)OC2=CC(=C(C(=C2)I)O)I | MeSHName = Reverse+triiodothyronine | ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}} | ChemSpiderID = 559294 | InChI = 1/C15H12I3NO4/c16-9-3-7(4-12(19)15(21)22)1-2-13(9)23-8-5-10(17)14(20)11(18)6-8/h1-3,5-6,12,20H,4,19H2,(H,21,22)/t12-/m0/s1 | InChIKey = HZCBWYNLGPIQRK-LBPRGKRZBV | StdInChI_Ref = {{stdinchicite|changed|chemspider}} | StdInChI = 1S/C15H12I3NO4/c16-9-3-7(4-12(19)15(21)22)1-2-13(9)23-8-5-10(17)14(20)11(18)6-8/h1-3,5-6,12,20H,4,19H2,(H,21,22)/t12-/m0/s1 | StdInChIKey_Ref = {{stdinchicite|changed|chemspider}} | StdInChIKey = HZCBWYNLGPIQRK-LBPRGKRZSA-N | ChEBI_Ref = {{ebicite|changed|EBI}} | ChEBI = 11684 | KEGG_Ref = {{keggcite|changed|kegg}} | KEGG = C07639 }} |Section2={{Chembox Properties | Formula = C₁₅H₁₂I₃NO₄ | MolarMass = 650.974 | Appearance = | Density = | MeltingPt = | BoilingPt = }} |Section3={{Chembox Hazards | MainHazards = | FlashPt = | AutoignitionPt = }} }} '''Reverse triiodothyronine''', also known as '''rT₃''', is an isomer of triiodothyronine (T₃).

Reverse T₃ is the third-most common iodothyronine the thyroid gland releases into the bloodstream, at 0.9%; tetraiodothyronine (levothyroxine, T₄) constitutes 90% and T₃ is 9%. However, 95% of rT₃ in human blood is made elsewhere in the body, as enzymes remove a particular iodine atom from T₄.<ref name="Chopra_1976">{{cite journal | author = Chopra IJ | title = An assessment of daily production and significance of thyroidal secretion of 3,3′,5′-triiodothyronine (reverse T3) in man | journal = J. Clin. Invest. | volume = 58 | issue = 1 | pages = 32–40 |date=July 1976 | pmid = 932209 | pmc = 333152 | doi = 10.1172/JCI108456 }}</ref>

The production of hormone by the thyroid gland is controlled by the hypothalamus and pituitary gland. The physiological activity of thyroid hormone is regulated by a system of enzymes that activate, inactivate or simply discard the prohormone T₄ and in turn functionally modify T₃ and rT₃. These enzymes operate under complex direction of systems including neurotransmitters, hormones, markers of metabolism and immunological signals.

The levels of rT₃ increase in conditions such as euthyroid sick syndrome because its clearance decreases while its production stays the same. The decreased clearance is possibly from lower thyroxine 5-deiodinase activity in the peripheral tissue or decreased liver uptake of rT₃.<ref>{{EMedicine|article|118651|Euthyroid Sick Syndrome}}</ref> In addition, increased rT₃ concentrations result from upregulated thyroxine 5-deiodinase activity in critical illness, starvation and fetal life.<ref name = "Chatzitomaris_2017">{{cite journal|last1=Chatzitomaris|first1=Apostolos|last2=Hoermann|first2=Rudolf|last3=Midgley|first3=John E.|last4=Hering|first4=Steffen|last5=Urban|first5=Aline|last6=Dietrich|first6=Barbara|last7=Abood|first7=Assjana|last8=Klein|first8=Harald H.|last9=Dietrich|first9=Johannes W.|title=Thyroid Allostasis–Adaptive Responses of Thyrotropic Feedback Control to Conditions of Strain, Stress, and Developmental Programming|journal=Frontiers in Endocrinology|date=20 July 2017|volume=8|page=163 |pmid=28775711|pmc=5517413|doi=10.3389/fendo.2017.00163|doi-access=free}}</ref>

==Reactions== [[Image:Iodothyronine deiodinase.png|thumb|left|400px|Synthesis of Reverse T₃ from T₄ via deiodination. Synthesis of T₃ and T₂ is also shown.]]{{clear|left}}

== References == {{reflist}}

==External links== * {{MeSH name|Triiodothyronine, Reverse}}

{{Thyroid hormone intermediates}} {{Xenobiotic-sensing receptor modulators}}

Category:Iodinated tyrosine derivatives Category:Thyroid