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Am J Physiol Regul Integr Comp Physiol (June 20, 2002). doi:10.1152/ajpregu.00015.2002
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Articles in PresS, published online ahead of print June 20, 2002
Am J Physiol Regu Physiol, 10.1152/ajpregu.00015.2002
Submitted on January 11, 2002
Accepted on May 17, 2002

Glucocorticoids, thyroid hormones and iodothyronine deiodinases in embryonic saltwater crocodiles

Caroline A Shepherdley1*, Christopher B Daniels2, Sandra Orgeig2, Samantha J Richardson3, Barbara K Evans1, and Veerle M Darras4

1 Department of Zoology, The University of Melbourne, Melbourne, Victoria, Australia
2 Department of Environmental Biology, Adelaide University, Adelaide, South Australia, Australia
3 Department of Biochemistry and Molecular Biology, The University of Melbourne, Melbourne, Victoria, Australia
4 Laboratory of Comparative Endocrinology, Catholic University of Leuven, Leuven, Belgium

* To whom correspondence should be addressed. E-mail: sjrich{at}unimelb.edu.au.

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), 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 T4 ORD activities in liver and kidney microsomes, and a decrease in the high-Km 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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