Ebbesson Lars O E, Björnsson Björn Th, Ekström Peter, Stefansson Sigurd O
Department Biology, University of Bergen, High Technology Centre, N-5020 Bergen, Norway.
Comp Biochem Physiol A Mol Integr Physiol. 2008 Dec;151(4):698-704. doi: 10.1016/j.cbpa.2008.08.017. Epub 2008 Aug 24.
To elucidate possible mechanisms behind the endocrine control of parr-smolt transformation, the daily plasma profiles in thyroid hormones (TH; free thyroxine (FT(4)), total thyroxine (TT(4)), and total 3,5,3'-triiodothyronine (TT(3))), growth hormone (GH) and cortisol were studied in Atlantic salmon parr and smolts under simulated-natural winter (8 L:16D) and spring (16.5 L:7.5D) photoperiods, respectively. Overall, TT(4), TT(3) and GH levels were higher in smolts than in parr, whereas FT(4) levels fluctuated within the same range in parr and smolts. Significant diurnal changes in plasma TH were present in parr. Both FT(4) and TT(4) levels increased during the photophase and decreased during the scotophase, while TT(3) levels followed an inverse pattern. Growth hormone showed no significant changes in parr. Changes in FT(4), TT(4), GH, and cortisol, but not TT(3), levels, were observed in smolts with peak levels during both the photophase and scotophase for FT(4), TT(4) and GH. Plasma cortisol was not assayed in parr but in smolts the peaks were associated with dusk and dawn. In addition to the general increases in TH, GH and cortisol, the distinct endocrine differences in nighttime levels between parr in the winter and smolts in the spring suggest different interactions between TH, GH, cortisol and melatonin at these different time points. These spring scotophase endocrine profiles may represent synergistic hormone interactions that promote smolt development, similar to the synergistic endocrine interactions shown to accelerate anuran metamorphosis. The variations in these diurnal rhythms between parr and smolts may represent part of the endocrine mechanism for the translation of seasonal information during salmon smoltification.
为阐明幼鲑-成鲑转变的内分泌控制背后的可能机制，分别在模拟自然冬季（8小时光照：16小时黑暗）和春季（16.5小时光照：7.5小时黑暗）光周期下，研究了大西洋鲑幼鲑和成鲑血浆中甲状腺激素（TH；游离甲状腺素（FT4）、总甲状腺素（TT4）和总三碘甲状腺原氨酸（TT3））、生长激素（GH）和皮质醇的每日变化情况。总体而言，成鲑的TT4、TT3和GH水平高于幼鲑，而FT4水平在幼鲑和成鲑中波动范围相同。幼鲑血浆TH存在显著的昼夜变化。FT4和TT4水平在光照期升高，在暗期降低，而TT3水平则呈现相反的模式。幼鲑的生长激素没有显著变化。在成鲑中观察到FT4、TT4、GH和皮质醇水平的变化，但TT3水平没有变化，FT4、TT4和GH在光照期和暗期均出现峰值。幼鲑血浆中未检测皮质醇，但在成鲑中，峰值与黄昏和黎明有关。除了TH、GH和皮质醇普遍升高外，冬季幼鲑和春季成鲑夜间水平的明显内分泌差异表明，在这些不同时间点，TH、GH、皮质醇和褪黑素之间存在不同的相互作用。这些春季暗期内分泌特征可能代表促进成鲑发育的协同激素相互作用，类似于已证明能加速无尾两栖类变态的协同内分泌相互作用。幼鲑和成鲑之间这些昼夜节律的变化可能代表了鲑鱼幼鲑化过程中季节性信息转化的内分泌机制的一部分。
