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 0 ,5 0 -tetraiodothyronine (T 4 ), and extrathyroidal outer ring deiodination (ORD) of the prohormone to 3,5,3 0 -triiodothyronine (T 3 ) 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 T 3 is still a controversial issue in teleosts. In this study, we investigated the regulation of the ORD pathway by cortisol and T 3 in different organs (liver, kidney, and gills) of Solea senegalensis and the involvement of T 3 in the control of branchial and renal Na C , K C -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 T 3 . Hepatic and renal ORD activities were up-regulated in cortisol-injected animals. T 3 -treated fish showed a prominent decrease in plasma-free T 4 levels, whereas ORD activities did not change significantly. Branchial and renal Na C , K C -ATPase activities were virtually unaffected by T 3 , but were transiently up-regulated by cortisol. We conclude that cortisol regulates local T 3 bioavailability in S. senegalensis via ORD in an organ-specific manner. Unlike T 3 , cortisol appears to be directly implicated in the up-regulation of branchial and renal Na

Deiodinases and thyroid metabolism disruption in teleost fish

“…However, such response was only observed in vivo, suggesting that growth hormone acts on the thyroid pathway indirectly (Sweeting and Eales, 1992b). More ambiguous results have been reported for cortisol, a hormone involved in stress response (Arjona et al, 2011;Brown et al, 1991).…”

Maternal Thyroid and Glucocorticoid Hormone Interactions in Larval Fish Development, and Their Applications in Aquaculture

“…Peripheral outer ring deiodination converts T 4 into 3,5,3'-triiodothyronine, or T 3 , which is an order of magnitude more biologically potent than T 4 (Orozco and Valverde, 2005). Cortisol promotes the conversion of T 4 into T 3 by activating outer ring deiodinase activity (Vijayan et al, 1988;Arjona et al, 2011), and increasing the T 3 /T 4 ratio is one mechanism by which cortisol promotes thyroid-mediated processes. Ontogenetic patterns in developing fishes that reflect this relationship can be seen in the golden sea bream, Sparus aurata; increasing cortisol levels are accompanied by a sharp increase in the ratio of T 3 /T 4 late in larval development, resulting in significant physiological and morphological changes (Szisch et al, 2005).…”

Dexamethasone modulates expression of genes involved in the innate immune system, growth and stress and increases susceptibility to bacterial disease in Senegalese sole (Solea senegalensis Kaup, 1858)

“…A negative correlation between plasma cortisol and plasma free T4 levels was observed after a salinity shift. These changes were associated to an increased renal and hepatic outer ring deiodination indicating that cortisol regulates T3 bioavailability in peripheral tissues [2,105]. In this work, we have quantified the expression of tgb, the precursor of THs in the thyroid gland.…”

“…This gene was proposed as a useful marker to monitor the thyroid activity during development due to a positive correlation between thyroglobulin mRNA transcripts and T4 levels observed in sole larvae [44]. The absence of variation of tgb mRNA suggests a peripheral instead of a central regulation of T3 synthesis by cortisol [2,104,105].…”