McQuillan H James, Lokman P Mark, Young Graham
Department of Zoology, University of Otago, Dunedin, New Zealand.
Gen Comp Endocrinol. 2003 Aug;133(1):154-63. doi: 10.1016/s0016-6480(03)00163-1.
Sex steroids appear to be responsible for hyperactivation of the hypothalamus-pituitary-interrenal (HPI) axis that occurs in mature semelparous Pacific salmon as a prelude to post-spawning (programmed) death. This study was undertaken to examine the direct effects of sex steroids on interrenal activity of semelparous (chinook salmon) and iteroparous (rainbow trout) salmonids using an in vitro incubation system. In addition, phenotypic sex differences in cortisol production by interrenals of sexually mature (spawning) rainbow trout and chinook salmon were investigated. Interrenal tissue from juvenile and sexually mature chinook salmon and rainbow trout was incubated for 48 h in culture medium containing either no steroid (controls), 1 microM estradiol (E2) or 1 microM 11-ketotestosterone (11-KT). This tissue was then challenged for 3h with either pregnenolone, dibutyryladenosine 3('):5(')-cyclic monophosphate (dbcAMP) or forskolin, or synthetic human adrenocorticotropic hormone (ACTH(1-24)). Sex differences in in vitro interrenal cortisol production were assessed using separate tissue pools challenged with the same agents. Cortisol in media was measured by radioimmunoassay. E2 suppressed the ability of juvenile chinook salmon interrenals to utilize pregnenolone as substrate for cortisol synthesis. In mature female chinook salmon the suppressive effect of E2 was less pronounced, but was observed as a reduced response of interrenals to both pregnenolone and dbcAMP. E2 did not affect ACTH(1-24) stimulated cortisol production. Immature and mature rainbow trout interrenals were both relatively insensitive to E2. 11-KT did not affect cortisol production by juvenile chinook salmon and juvenile or mature rainbow trout, and had only minor effects in male and female spawning chinook salmon. In mature chinook salmon and rainbow trout, the interrenals of females were more responsive to ACTH stimulation and showed a greater utilization of pregnenolone as a substrate than interrenals of males. Mature female rainbow trout were also more responsive to dbcAMP stimulation than males. The results of this study suggest that the onset of sexual maturation and gonadal steroid production may contribute to sexually dimorphic cortisol responses in vitro.
性类固醇似乎是导致成熟的一次性产卵的太平洋鲑鱼下丘脑 - 垂体 - 肾间（HPI）轴过度激活的原因，这种激活是产卵后（程序性）死亡的前奏。本研究旨在使用体外培养系统研究性类固醇对一次性产卵（奇努克鲑）和多次产卵（虹鳟）鲑科鱼类肾间活动的直接影响。此外，还研究了性成熟（产卵期）虹鳟和奇努克鲑肾间皮质醇产生的表型性别差异。将幼年和性成熟的奇努克鲑以及虹鳟的肾间组织在不含类固醇（对照）、含有1微摩尔雌二醇（E2）或1微摩尔11 - 酮睾酮（11 - KT）的培养基中培养48小时。然后用孕烯醇酮、二丁酰腺苷3':5'-环磷酸（dbcAMP）或福斯可林，或合成人促肾上腺皮质激素（ACTH(1 - 24)）对该组织进行3小时的刺激。使用受相同试剂刺激的单独组织池评估体外肾间皮质醇产生的性别差异。通过放射免疫测定法测量培养基中的皮质醇。E2抑制幼年奇努克鲑肾间利用孕烯醇酮作为皮质醇合成底物的能力。在成熟的雌性奇努克鲑中，E2的抑制作用不太明显，但表现为肾间对孕烯醇酮和dbcAMP的反应降低。E2不影响ACTH(1 - 24)刺激的皮质醇产生。未成熟和成熟的虹鳟肾间对E2都相对不敏感。11 - KT不影响幼年奇努克鲑以及幼年或成熟虹鳟的皮质醇产生，对产卵期的雄性和雌性奇努克鲑只有轻微影响。在成熟的奇努克鲑和虹鳟中，雌性的肾间对ACTH刺激的反应更强，并且比雄性的肾间更能将孕烯醇酮作为底物利用。成熟的雌性虹鳟对dbcAMP刺激的反应也比雄性更强。本研究结果表明，性成熟和性腺类固醇产生的开始可能导致体外皮质醇反应的性别二态性。
