McCormick Stephen D, Regish Amy, O'Dea Michael F, Shrimpton J Mark
USGS, Conte Anadromous Fish Research Center, One Migratory Way, PO Box 796, Turners Falls, MA 01376, USA.
Gen Comp Endocrinol. 2008 May 15;157(1):35-40. doi: 10.1016/j.ygcen.2008.03.024. Epub 2008 Mar 31.
It has long been held that cortisol, acting through a single receptor, carries out both glucocorticoid and mineralocorticoid actions in teleost fish. The recent finding that fish express a gene with high sequence similarity to the mammalian mineralocorticoid receptor (MR) suggests the possibility that a hormone other than cortisol carries out some mineralocorticoid functions in fish. To test for this possibility, we examined the effect of in vivo cortisol, 11-deoxycorticosterone (DOC) and aldosterone on salinity tolerance, gill Na(+),K(+)-ATPase (NKA) activity and mRNA levels of NKA alpha 1a and alpha 1b in Atlantic salmon. Cortisol treatment for 6-14 days resulted in increased, physiological levels of cortisol, increased gill NKA activity and improved salinity tolerance (lower plasma chloride after a 24h seawater challenge), whereas DOC and aldosterone had no effect on either NKA activity or salinity tolerance. NKA alpha 1a and alpha 1b mRNA levels, which increase in response to fresh water and seawater acclimation, respectively, were both upregulated by cortisol, whereas DOC and aldosterone were without effect. Cortisol, DOC and aldosterone had no effect on gill glucocorticoid receptor GR1, GR2 and MR mRNA levels, although there was some indication of possible upregulation of GR1 by cortisol (p=0.07). The putative GR blocker RU486 inhibited cortisol-induced increases in salinity tolerance, NKA activity and NKA alpha 1a and alpha 1b transcription, whereas the putative MR blocker spironolactone had no effect. The results provide support that cortisol, and not DOC or aldosterone, is involved in regulating the mineralocorticoid functions of ion uptake and salt secretion in teleost fish.
长期以来，人们一直认为皮质醇通过单一受体发挥作用，在硬骨鱼中执行糖皮质激素和盐皮质激素的功能。最近的研究发现，鱼类表达一种与哺乳动物盐皮质激素受体（MR）具有高度序列相似性的基因，这表明可能存在一种不同于皮质醇的激素在鱼类中执行一些盐皮质激素的功能。为了验证这种可能性，我们研究了体内注射皮质醇、11-脱氧皮质酮（DOC）和醛固酮对大西洋鲑鱼耐盐性、鳃Na(+)，K(+)-ATP酶（NKA）活性以及NKA α1a和α1b mRNA水平的影响。皮质醇处理6-14天导致皮质醇水平升高至生理水平，鳃NKA活性增加，耐盐性提高（24小时海水刺激后血浆氯化物降低），而DOC和醛固酮对NKA活性或耐盐性均无影响。NKA α1a和α1b mRNA水平分别在淡水和海水驯化后升高，二者均被皮质醇上调，而DOC和醛固酮则无此作用。皮质醇、DOC和醛固酮对鳃糖皮质激素受体GR1、GR2和MR mRNA水平均无影响，不过有迹象表明皮质醇可能上调GR1（p=0.07）。推测的GR阻滞剂RU486抑制了皮质醇诱导的耐盐性增加、NKA活性以及NKA α1a和α1b转录，而推测的MR阻滞剂螺内酯则无作用。这些结果支持了在硬骨鱼中，参与调节离子摄取和盐分分泌的盐皮质激素功能的是皮质醇，而非DOC或醛固酮。
