Yada T, Kobayashi T, Urano A, Hirano T
Ocean Research Institute, University of Tokyo, Japan.
J Exp Zool. 1992 Jul 1;262(4):420-5. doi: 10.1002/jez.1402620408.
To examine the changes in secretion of growth hormone (GH) and prolactin (PRL) with reference to their osmoregulatory roles, changes in pituitary mRNA levels and plasma concentrations of these hormones were examined during seawater adaptation in silvery juveniles (smolts) and precociously mature males (dark parr) of amago salmon (Oncorhynchus rhodurus). Transfer to seawater increased plasma sodium levels in both smolts and dark parr. Smolts adjusted their plasma sodium to the level associated with seawater-adaptation (165 mEq/liter) within 3 days, whereas no adjustment was seen in dark parr; the latter failed to survive in seawater for more than 3 days. In smolts, plasma GH levels increased significantly 1 day after transfer, whereas there was no significant change in dark parr. An increase in GH mRNA levels was observed in smolts in association with increased plasma GH, whereas there was no change in dark parr. In contrast, a reduction in plasma PRL levels was consistently observed in both smolts and dark parr after transfer to seawater. However, there was no significant change in PRL mRNA levels in either smolts or dark parr. These results suggest that both gene expression and release of GH are activated by seawater transfer only in smolts with adequate seawater adaptability, whereas PRL gene expression is decreased after seawater transfer regardless of seawater adaptability.
为研究生长激素（GH）和催乳素（PRL）分泌的变化及其渗透调节作用，我们检测了红点鲑（Oncorhynchus rhodurus）银色幼鱼（洄游期幼鱼）和早熟雄鱼（暗色幼鲑）在适应海水过程中垂体mRNA水平及这些激素的血浆浓度变化。转移至海水中后，洄游期幼鱼和暗色幼鲑的血浆钠水平均升高。洄游期幼鱼在3天内将血浆钠水平调整至与海水适应相关的水平（165 mEq/升），而暗色幼鲑未见调整；后者在海水中存活不超过3天。在洄游期幼鱼中，转移1天后血浆GH水平显著升高，而暗色幼鲑则无显著变化。随着血浆GH升高，洄游期幼鱼中观察到GH mRNA水平增加，而暗色幼鲑则无变化。相反，转移至海水后，在洄游期幼鱼和暗色幼鲑中均持续观察到血浆PRL水平降低。然而，洄游期幼鱼和暗色幼鲑的PRL mRNA水平均无显著变化。这些结果表明，只有在具有足够海水适应性的洄游期幼鱼中，海水转移才会激活GH的基因表达和释放，而无论海水适应性如何，海水转移后PRL基因表达均会降低。
