Differential regulation of the two forms of gonadotropin-releasing hormone (mGnRH and cGnRH-II) by sex steroids in the European female silver eel (Anguilla anguilla).
Differential regulation of the two forms of gonadotropin-releasing hormone (mGnRH and cGnRH-II) by sex steroids in the European female silver eel (Anguilla anguilla).
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欧洲雌性银鳗（Anguilla anguilla）中性类固醇对两种形式促性腺激素释放激素（mGnRH 和 cGnRH-II）的差异调节。
作者：
M. Montero;N. Le Belle;J. King;R. Millar;S. Dufour
使用特定的放射免疫测定法研究了类固醇对鳗鱼中存在的两种促性腺激素释放激素 (GnRH) 形式（哺乳动物 GnRH、mGnRH 和鸡 GnRH-II、cGnRH-II）以及促性腺激素 (GTH) 的影响。雌性银鳗接受各种类固醇（雌二醇、睾酮、雄烯二酮、5α-雄甾烷-3β、17β-二醇）的长期治疗。雌二醇或雌二醇与雄激素的组合可引起大脑和垂体 mGnRH 水平以及垂体 GTH 水平的增加，而单独给予雄激素则没有显着效果。相反，雄激素或其与雌二醇的组合降低了大脑中的cGnRH-II水平（这种形式在垂体中仍然检测不到），单独给予雌二醇没有显着效果。这项工作表明，两种形式的 GnRH 受到类固醇的差异调节，对 mGnRH（以及 GTH）具有雌激素依赖性正反馈，对 cGnRH-II 具有雄激素依赖性负反馈。这些数据与之前在成熟雌性鳗鱼（通过刺激雌激素和雄激素产生的促性腺激素治疗诱导）中获得的结果一致，显示 mGnRH 和 GTH 水平增加，以及 cGnRH-II 水平下降 [1]。 mGnRH-GTH 轴上类固醇的正反馈增加了这一假设的可信度，根据该假设，mGnRH 将是参与控制促性腺功能的主要形式。这种正反馈将发挥重要作用，放大这种鱼类的青春期促性腺轴刺激。
The effect of steroids on the two gonadotropin-releasing hormone (GnRH) forms present in the eel (mammalian GnRH, mGnRH and chicken GnRH-II, cGnRH-II), as well as on gonadotropin (GTH), was studied using specific radioimmunoassays. Female silver eels received chronic treatments with various steroids (estradiol, testosterone, androstenedione, 5 alpha-androstane-3 beta, 17 beta-diol). Estradiol or the combination of estradiol and androgens induced increases in brain and pituitary mGnRH levels and pituitary GTH level, whereas androgens given alone had no significant effect. In contrast, androgens or their combination with estradiol reduced brain cGnRH-II levels (this form remaining undetectable in the pituitary), estradiol given alone having no significant effect. This work demonstrates that the two forms of GnRH undergo a differential regulation by steroids, with a positive estrogen-dependent feedback on mGnRH (as well as on GTH) and a negative androgen-dependent feedback on cGnRH-II. These data are in agreement with previous results obtained in experimentally matured female eels (induced by a gonadotropic treatment which stimulates the production of both estrogens and androgens) showing increases in mGnRH and GTH levels, as well as a decrease in cGnRH-II [1]. The positive feedback of steroids on the mGnRH-GTH axis adds credence to the hypothesis according to which mGnRH would be the main form involved in the control of the gonadotropic function. This positive feedback would play an important role, amplifying pubertal stimulation of the gonadotropic axis, in this fish species.