Morin P P, Hara T J, Eales J G
Department of Zoology, University of Manitoba, Winnipeg, Canada.
Gen Comp Endocrinol. 1993 May;90(2):142-56. doi: 10.1006/gcen.1993.1069.
Outer-ring deiodinase (ORD) and inner-ring deiodinase (IRD) pathways for L-thyroxine (T4) were examined in the microsomes of tissues of 20-month-old Atlantic salmon induced to undergo parr-smolt transformation (PST) in late February and March by imposing a 16-hr photoperiod. Smolt external characteristics, decline in condition factor, increases in brain-somatic index, cardiac-somatic index, gill-somatic index, gill Na+/K+ ATPase activity, and food consumption developed progressively during the 5-week study. Plasma T4 (4.1 ng/ml, Week 1) rose to 13.5 and 12.5 ng/ml (Weeks 3 and 4) and fell to 7.5 ng/ml (Week 5). Plasma T3 rose from 2.1 ng/ml (Week 1) to 3.8 ng/ml (Week 2) and fell to 2.4 ng/ml (Week 5). T4ORD activity occurred in liver, heart, gill, brain, and skeletal muscle, increasing in liver and heart between Weeks 1 and 2, and in brain between Weeks 4 and 5. Only liver T4ORD activity was correlated (r = +0.946) with plasma T3 concentrations, suggesting that hepatic T4ORD may determine the plasma T3 concentration. For hepatic T4ORD the mean Km was 0.42 nM and the mean Vmax 1.2 pmols T4 converted.hr-1.mg microsomal protein-1. HPLC analysis revealed 3,3',5-T3(rT3) and 3,3'-diiodo-L-thyronine, as evidence of T4IRD activity, but only in liver and brain. The lower bound estimates of T4IRD activities to generate rT3 were 28% (liver) and 50% (brain) of the respective T4ORD activities. Brain T4IRD increased progressively during PST. In post-smolts in later October, plasma T3 concentrations and both hepatic and brain T4ORD and T4IRD activities were low, but some rT3 was produced. We conclude that during induced PST in Atlantic salmon (i) T4ORD activity increases in liver, heart, and brain, but not in gill or skeletal muscles; (ii) the hepatic T4ORD is highly correlated with plasma T3 and may therefore determine plasma T3; and (iii) there are changes in T4ORD and T4IRD in brain, which may reflect regulation of intracellular thyroid hormone metabolism in that tissue. However, it remains to be determined how changes in deiodinase activity relate to the surge in plasma T4 and the role of thyroid hormones during PST.
通过设置16小时光照周期，对2月下旬和3月诱导进行降海型幼鱼-成鱼转变（PST）的20月龄大西洋鲑组织微粒体中的L-甲状腺素（T4）外环脱碘酶（ORD）和内环脱碘酶（IRD）途径进行了研究。在为期5周的研究中，幼鲑的外部特征逐渐显现，肥满度下降，脑体指数、心脏体指数、鳃体指数、鳃Na+/K+ ATP酶活性和食物消耗量增加。血浆T4（第1周为4.1 ng/ml）在第3周和第4周升至13.5和12.5 ng/ml，在第5周降至7.5 ng/ml。血浆T3从第1周的2.1 ng/ml升至第2周的3.8 ng/ml，在第5周降至2.4 ng/ml。T4ORD活性存在于肝脏、心脏、鳃、脑和骨骼肌中，在第1周和第2周肝脏和心脏中的活性增加，在第4周和第5周脑内活性增加。只有肝脏中的T4ORD活性与血浆T3浓度相关（r = +0.946），这表明肝脏中的T4ORD可能决定血浆T3浓度。肝脏T4ORD的平均Km为0.42 nM，平均Vmax为1.2 pmol T4转化·小时-1·毫克微粒体蛋白-1。高效液相色谱分析显示，存在3,3',5-T3（反T3，rT3）和3,3'-二碘-L-甲状腺原氨酸，这是T4IRD活性的证据，但仅在肝脏和脑中存在。产生rT3的T4IRD活性下限估计分别为各自T4ORD活性的28%（肝脏）和50%（脑）。在PST过程中，脑内T4IRD逐渐增加。在10月下旬的降海型幼鱼中，血浆T3浓度以及肝脏和脑内的T4ORD和T4IRD活性均较低，但仍产生了一些反T3。我们得出结论，在大西洋鲑诱导的PST过程中：（i）肝脏、心脏和脑中的T4ORD活性增加，而鳃或骨骼肌中没有增加；（ii）肝脏T4ORD与血浆T3高度相关，因此可能决定血浆T3；（iii）脑中的T4ORD和T4IRD发生变化，这可能反映了该组织中细胞内甲状腺激素代谢的调节。然而，脱碘酶活性的变化如何与血浆T4的激增以及PST过程中甲状腺激素的作用相关，仍有待确定。
