title: Effects of cortisol and thyroid hormone on peripheral outer ring deiodination and osmoregulatory parameters in the Senegalese sole (Solea senegalensis).
abstract: The thyroid gland in fish mainly secretes the thyroid prohormone 3,5,3',5'-tetraiodothyronine (T₄), and extrathyroidal outer ring deiodination (ORD) of the prohormone to 3,5,3'-triiodothyronine (T₃) is pivotal in thyroid hormone economy. Despite its importance in thyroid hormone metabolism, factors that regulate ORD are still largely unresolved in fish. In addition, the osmoregulatory role of T₃ is still a controversial issue in teleosts. In this study, we investigated the regulation of the ORD pathway by cortisol and T₃ in different organs (liver, kidney, and gills) of Solea senegalensis and the involvement of T₃ in the control of branchial and renal Na(+), K(+)-ATPase activity, a prime determinant of the hydromineral balance in teleosts. Animals were treated with i.p. slow-release coconut oil implants containing cortisol or T₃. Hepatic and renal ORD activities were up-regulated in cortisol-injected animals. T₃-treated fish showed a prominent decrease in plasma-free T₄ levels, whereas ORD activities did not change significantly. Branchial and renal Na(+), K(+)-ATPase activities were virtually unaffected by T₃, but were transiently up-regulated by cortisol. We conclude that cortisol regulates local T₃ bioavailability in S. senegalensis via ORD in an organ-specific manner. Unlike T₃, cortisol appears to be directly implicated in the up-regulation of branchial and renal Na(+), K(+)-ATPase activities.
authors.affiliation: Department of Animal Physiology, Institute for Water and Wetland Research, Faculty of Science, Radboud University Nijmegen, Nijmegen, The Netherlands. f.arjona@science.ru.nl
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Arjona
authors.forename: Luis
authors.initials: L
authors.lastname: Vargas-Chacoff
authors.forename: María P
authors.initials: MP
authors.lastname: Martín Del Río
authors.forename: Gert
authors.initials: G
authors.lastname: Flik
authors.forename: Juan M
authors.initials: JM
authors.lastname: Mancera
authors.forename: Peter H M
authors.initials: PH
authors.lastname: Klaren
mesh_terms: D000818:Animals; D005412:Flatfishes / Q000378:metabolism*; D005880:Gills / Q000187:drug effects / Q000201:enzymology; D006854:Hydrocortisone / Q000494:pharmacology*; D007453:Iodide Peroxidase / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000201:enzymology; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013974:Thyroxine / Q000097:blood / Q000378:metabolism; D014284:Triiodothyronine / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects; D014882:Water-Electrolyte Balance / Q000187:drug effects*
chemical_list: D014284:Triiodothyronine; D007453:Iodide Peroxidase; D000254:Sodium-Potassium-Exchanging ATPase; D013974:Thyroxine; D006854:Hydrocortisone