title: Effects of iodothyronines on the hepatic outer-ring deiodinating pathway in killifish.
abstract: Substrate availability has been thought to be a major regulator of the outer-ring deiodinating pathway (ORD) in fish. However, current information strongly suggests that while fish iodothyronine deiodinase type 2 (D2) responds to iodothyronines in the same manner as its mammalian counterpart, fish deiodinase type 1 (D1) exhibits a distinct response. Furthermore, 3,5-T2, generally considered to be an inactive product of iodothyronine metabolism, has recently been described as bioactive, but its effects upon D1 and D2 are not yet known. We examined the effect that short-term immersion in T4, T3, and 3,5-T2 (0.1 microM; 12 or 24 h) exerts on both D1 and D2 activities and on the levels of expression of D1 and D2 mRNAs in killifish liver. In agreement with previous reports in teleosts, no iodothyronine exerted a significant effect on D1 enzymatic activity. However, all three iodothyronines significantly decreased D2 activity. Furthermore, at 24 h post-immersion T4, T3, and 3,5-T2 inhibited both D1 and D2 transcription. Together, the present results confirm the differential effect of iodothyronines upon the hepatic ORD pathway in fish and show that this effect can occur at a transcriptional level. Furthermore, we provide the first evidence that 3,5-T2 can affect both activity and transcription of hepatic deiodinases in teleosts.
authors.affiliation: Instituto de Neurobiología, Universidad Nacional Autónoma de México, Campus UNAM-UAQ-Juriquilla, Queretaro 76230, Qro, Mexico.
authors.forename: Carlota
authors.initials: C
authors.lastname: García-G
authors.forename: Michael C
authors.initials: MC
authors.lastname: Jeziorski
authors.forename: Carlos
authors.initials: C
authors.lastname: Valverde-R
authors.forename: Aurea
authors.initials: A
authors.lastname: Orozco
mesh_terms: D000818:Animals; D004104:Diiodothyronines / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D023781:Fundulidae / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D007453:Iodide Peroxidase / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008297:Male; D016133:Polymerase Chain Reaction / Q000379:methods; D012333:RNA, Messenger / Q000032:analysis; D013961:Thyroid Gland / Q000378:metabolism*; D013974:Thyroxine / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology; D000097564:Iodothyronine Deiodinase Type II
chemical_list: D004104:Diiodothyronines; D007453:Iodide Peroxidase; D012333:RNA, Messenger; D013974:Thyroxine; D014284:Triiodothyronine; D000097564:Iodothyronine Deiodinase Type II; C030103:3,5-diiodothyronine; C109812:iodothyronine deiodinase type I