Walpita Chaminda N, Grommen Sylvia V H, Darras Veerle M, Van der Geyten Serge
Laboratory of Comparative Endocrinology, Zoological institute, KU Leuven, Naamsestraat 61, B-3000 Leuven, Belgium.
Gen Comp Endocrinol. 2007 Jan 1;150(1):18-25. doi: 10.1016/j.ygcen.2006.07.002. Epub 2006 Aug 17.
The existence of an interaction between the adrenal/interrenal axis and the thyroidal axis has since long been established in vertebrates, including fish. However, in contrast to mammals, birds and amphibians, no effort was made in fish to expand these studies beyond the level of measuring plasma thyroid hormones. We therefore set out to examine the acute effects of a single dose of dexamethasone (DEX) on plasma thyroxine (T(4)) and 3,5,3'-triiodothyronine (T(3)) levels, as well as on the activity and mRNA expression of the different iodothyronine deiodinases in liver, gills, kidney and brain in Nile tilapia. To take into account the effect of handling stress, this treatment was compared both to a non-treated and to a saline injected group. In general, the observed changes were acute (3 and 6h) while values had returned to control levels by 24h post-injection. Only DEX administration caused an acute drop in circulating T(3) levels compared to non-treated animals, while none of the treatments affected plasma T(4) levels. This indicates that the DEX induced decrease in plasma T(3) levels was not due to a lowered thyroidal hormone production and secretion. DEX injection provoked a decrease in peripheral T(3) production capacity via a decrease in hepatic outer ring deiodination activity (both D1 and D2), whereas T(3) clearance increased by induction of the inner ring deiodinating D3 pathway in liver and in gills. Deiodination activities in kidney and brain were not affected. Effects of saline injection were only observed in liver, where D1 activity decreased and D3 activity increased as in the DEX group, but to a lesser extent. Real-time PCR showed that the changes in hepatic D3 were clearly regulated at the pretranslational level, while this was not confirmed for the other changes. Our results show that both handling stress and DEX injection acutely disturb peripheral deiodination activity in Nile tilapia. However, the effects of the long acting glucocorticoid analogue are more pronounced and result in a decrease in circulating T(3) availability.
肾上腺/肾间轴与甲状腺轴之间存在相互作用，这在包括鱼类在内的脊椎动物中早已得到证实。然而，与哺乳动物、鸟类和两栖动物不同的是，鱼类并未在测量血浆甲状腺激素水平之上进一步拓展这些研究。因此，我们着手研究单剂量地塞米松（DEX）对尼罗罗非鱼血浆甲状腺素（T4）和3,5,3'-三碘甲状腺原氨酸（T3）水平的急性影响，以及对肝脏、鳃、肾脏和大脑中不同碘甲状腺原氨酸脱碘酶活性和mRNA表达的影响。为了考虑处理应激的影响，将该处理组与未处理组和注射生理盐水组进行了比较。一般来说，观察到的变化是急性的（3小时和6小时），而在注射后24小时时，各项指标已恢复到对照水平。与未处理的动物相比，仅DEX给药导致循环T3水平急性下降，而所有处理均未影响血浆T4水平。这表明DEX诱导的血浆T3水平下降并非由于甲状腺激素产生和分泌减少。DEX注射通过降低肝脏外环脱碘活性（D1和D2），导致外周T3产生能力下降，而通过诱导肝脏和鳃中的内环脱碘D3途径，T3清除增加。肾脏和大脑中的脱碘活性未受影响。仅在肝脏中观察到注射生理盐水的影响，其中D1活性降低，D3活性增加，与DEX组情况相同，但程度较轻。实时PCR显示，肝脏中D3的变化在翻译前水平受到明显调控，而其他变化未得到证实。我们的结果表明，处理应激和DEX注射都会急性扰乱尼罗罗非鱼的外周脱碘活性。然而，长效糖皮质激素类似物的影响更为显著，导致循环T3可用性降低。
