Lock E J, Ornsrud R, Aksnes L, Spanings F A T, Waagbø R, Flik G
National Institute of Nutrition and Seafood Research, PO Box 2029 Nordnes, N-5817, Bergen, Norway.
J Endocrinol. 2007 Jun;193(3):459-71. doi: 10.1677/JOE-06-0198.
Seaward migration of Salmo salar is preceded by preparatory physiological adaptations (parr-smolt transformation) to allow for a switch from freshwater (FW) to seawater (SW), which also means a switch in ambient calcium from hypocalcic (<1 mM Ca(2+)) to the plasma (~1.25 mM Ca(2+)) and to strongly hypercalcic (8-12 mM Ca(2+)). Uptake, storage (skeleton, scales) and excretion of calcium need careful regulation. In fish, the vitamin D endocrine system plays a rather enigmatic role in calcium physiology. Here, we give direct evidence for calcitriol involvement in SW migration. We report the full sequence of the nuclear vitamin D receptor (sVDR0) and two alternatively spliced variants resulting from intron retention (sVDR1 and sVDR2). In FW parr, SW adapting smolts, and in SW adults, plasma concentrations of 25(OH)D(3) and 24,25(OH)(2)D(3) did not change significantly. Plasma calcitriol concentrations were lowest in FW parr, doubled during smoltification and remained elevated in SW adults. Increased calcitriol coincided with a twofold decrease in sVDR mRNA levels in gill, intestine, and kidney of FW smolts and SW adults, when compared with parr. Clearly, there was a negative feedback and dynamic response of the vitamin D endocrine system during parr-smolt transformation. The onset of these dynamic changes in FW parr warrants a further search for the endocrines that initiate these changes. We speculate that the vitamin D system plays a crucial role in calcium and phosphorus handling in Atlantic salmon.
大西洋鲑向海洄游之前会经历生理上的适应性准备（幼鱼 - 稚鱼转变），以实现从淡水（FW）到海水（SW）的转变，这也意味着环境钙浓度从低钙（<1 mM Ca(2+)）转变为血浆钙浓度（约1.25 mM Ca(2+)），并最终转变为高钙状态（8 - 12 mM Ca(2+)）。钙的摄取、储存（骨骼、鳞片）和排泄需要精细调节。在鱼类中，维生素D内分泌系统在钙生理过程中发挥着相当神秘的作用。在此，我们提供了1,25 - 二羟维生素D3参与海水洄游的直接证据。我们报道了核维生素D受体（sVDR0）的完整序列以及由内含子保留产生的两个可变剪接变体（sVDR1和sVDR2）。在淡水幼鱼、适应海水的稚鱼以及海水成鱼中，25(OH)D(3)和24,25(OH)(2)D(3)的血浆浓度没有显著变化。血浆1,25 - 二羟维生素D3浓度在淡水幼鱼中最低，在稚鱼化过程中翻倍，并在海水成鱼中保持升高。与幼鱼相比，淡水稚鱼和海水成鱼的鳃、肠道和肾脏中，1,25 - 二羟维生素D3增加的同时，sVDR mRNA水平下降了两倍。显然，在幼鱼 - 稚鱼转变过程中，维生素D内分泌系统存在负反馈和动态响应。淡水幼鱼中这些动态变化的起始促使我们进一步寻找引发这些变化的内分泌物质。我们推测维生素D系统在大西洋鲑的钙和磷处理中起着关键作用。
