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Glucocorticoids, thyroid hormones, and iodothyronine deiodinases in embryonic saltwater crocodiles
Shepherdley, C.A.; Daniels, C.B.; Orgeig, S.; Richardson, S.J.; Evans, B.K.; Darras, V.M. (2002). Glucocorticoids, thyroid hormones, and iodothyronine deiodinases in embryonic saltwater crocodiles. American Journal of Physiology-Regulatory Integrative and Comparative Physiology 283(5): R1155-R1163. dx.doi.org/10.1152/ajpregu.00015.2002
In: American Journal of Physiology-Regulatory Integrative and Comparative Physiology: Bethesda. ISSN 0363-6119, more
Peer reviewed article  

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Keywords
Author keywords
    reptile; development; outer ring deiodination; inner ring deiodination;liver; kidney

Authors  Top 
  • Shepherdley, C.A.
  • Daniels, C.B.
  • Orgeig, S.
  • Richardson, S.J.
  • Evans, B.K.
  • Darras, V.M.

Abstract
    We investigated the relationship between glucocorticoids, thyroid hormones, and outer ring and inner ring deiodinases (ORD and IRD) during embryonic development in the saltwater crocodile (Crocodylus porosus). We treated the embryos with the synthetic glucocorticoid dexamethasone (Dex), 3,3′,5-triiodothyronine (T3), and a combination of these two hormones (Dex + T3). The effects of these treatments were specific in different tissues and at different stages of development and also brought about changes in plasma concentrations of free thyroid hormones and corticosterone. Administration of Dex to crocodile eggs resulted in a decrease in 3,3′,5,5′-tetraiodothyronine (T4) ORD activities in liver and kidney microsomes, and a decrease in the high-K m rT3 ORD activity in kidney microsomes, on day 60 of incubation. Dex treatment increased the T4 ORD activity in liver microsomes, but not kidney microsomes, on day 75 of incubation. Dex administration decreased T3 IRD activity in liver microsomes. However, this decrease did not change plasma-free T3 concentrations, which suggests that free thyroid hormone levels are likely to be tightly regulated during development.

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