Geven Edwin J W, Flik Gert, Klaren Peter H M
Department of Animal Physiology, Faculty of Science, Institute for Water and Wetland Research, Radboud University Nijmegen, Nijmegen, The Netherlands.
J Endocrinol. 2009 Jan;200(1):117-23. doi: 10.1677/JOE-08-0410. Epub 2008 Oct 17.
In teleostean fishes the hypothalamic-pituitary-thyroid axis (HPT axis) and the hypothalamic-pituitary-interrenal axis (HPI axis) regulate the release of thyroid hormones (THs) and cortisol respectively. Since many actions of both hormones are involved in the regulation of metabolic processes, communication between both signal pathways can be anticipated. In this study, we describe central and peripheral sites for direct interaction between mediators of both neuroendocrine axes in the common carp (Cyprinus carpio). Despite suggestions in the literature that CRH is thyrotropic in some fish; we were not able to establish stimulatory effects of CRH on the expression of the pituitary TSHbeta subunit gene. In preoptic area tissue incubated with 10(-7) M thyroxine (T(4)) a 2 x 9-fold increase in the expression of CRH-binding protein (CRHBP) was observed. Thus, T(4) could reduce the bioavailable hypothalamic crh via the up regulation of crhbp expression and hence down regulate the HPI axis. At the peripheral level, cortisol (10(-6) M), ACTH (10(-7) M), and alpha-MSH (10(-7) M) stimulate the release of T(4) from kidney and head kidney fragments, which contain all functional thyroid follicles in carp, by two- to fourfold. The substantiation of three pituitary thyrotropic factors, viz. TSH, ACTH, and alpha-MSH, in common carp, allows for an integration of central thyrotropic signals. Clearly, two sites for interaction between the HPT axis, the HPI axis, and alpha-MSH are present in common carp. These interactions may be key to the proper regulation of general metabolism in this fish.
在硬骨鱼类中，下丘脑 - 垂体 - 甲状腺轴（HPT轴）和下丘脑 - 垂体 - 肾间轴（HPI轴）分别调节甲状腺激素（THs）和皮质醇的释放。由于这两种激素的许多作用都参与了代谢过程的调节，因此可以预期这两种信号通路之间会存在相互作用。在本研究中，我们描述了鲤鱼（Cyprinus carpio）中这两种神经内分泌轴的介质之间直接相互作用的中枢和外周位点。尽管文献中有观点认为促肾上腺皮质激素释放激素（CRH）在某些鱼类中具有促甲状腺作用，但我们未能证实CRH对垂体促甲状腺激素β亚基基因表达有刺激作用。在与10⁻⁷ M甲状腺素（T₄）孵育的视前区组织中，观察到促肾上腺皮质激素释放激素结合蛋白（CRHBP）的表达增加了2至9倍。因此，T₄可通过上调CRHBP表达来降低下丘脑可利用的CRH，从而下调HPI轴。在外周水平，皮质醇（10⁻⁶ M）、促肾上腺皮质激素（ACTH，10⁻⁷ M）和α - 促黑素（α - MSH，10⁻⁷ M）可使鲤鱼肾脏和头肾组织（其中包含鲤鱼所有功能性甲状腺滤泡）释放的T₄增加2至4倍。在鲤鱼中证实了三种垂体促甲状腺因子，即促甲状腺激素（TSH）、促肾上腺皮质激素（ACTH）和α - 促黑素（α - MSH），这使得中枢促甲状腺信号得以整合。显然，鲤鱼中存在HPT轴、HPI轴和α - MSH之间相互作用的两个位点。这些相互作用可能是该鱼类整体代谢正常调节的关键。
