Murthy C K, Peter R E
Department of Zoology, University of Alberta, Edmonton, Canada.
Gen Comp Endocrinol. 1994 Apr;94(1):78-91. doi: 10.1006/gcen.1994.1062.
In goldfish, two native gonadotropin-releasing hormone (GnRH) peptides, salmon GnRH (sGnRH) and chicken-II GnRH (cGnRH-II), stimulate gonadotropin (GTH-II) and growth hormone (GH) secretion. In the present study we tested whether sGnRH and cGnRH-II act through different or the same population of GnRH receptors on GTH and GH cells, using various approaches. A GnRH antagonist [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]sGnRH (analog C) equally inhibited GTH-II release by sGnRH and cGnRH-II. Similarly, [Ac-D(2)Nal1,4Cl-D-Phe2,D-(3)Pal3,6]cGnRH-II (analog N) suppressed GTH-II stimulation by the two GnRH peptides equally. Further, in the continued presence of 100 nM sGnRH, a 100 nM pulse of cGnRH-II failed to cause additional GTH-II release and vice versa. Prolonged exposure of pituitary fragments to 100 nM sGnRH or cGnRH-II resulted in desensitization and reduced the GTH-II response to a subsequent pulse of either sGnRH or cGnRH-II equally. All these results indicate that both sGnRH and cGnRH-II act through the same population of GnRH receptors on gonadotrophs. Similarly, the GH responses obtained with (i) analog N treatment, (ii) pulse challenge to cGnRH-II during prolonged sGnRH treatment and vice versa, and (iii) desensitization studies suggest that both sGnRH and cGnRH-II act through the same population of GnRH receptors on somatotrophs. However, the properties of GnRH receptors on GTH-II and GH cells are different. Analog C stimulated GH release but not GTH-II release. In contrast, [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,D-Arg6]mGnRH stimulated GTH-II release but weakly suppressed GH release. These results indicate that sGnRH and cGnRH-II act on the same population of receptors on GTH cells and on a functionally distinct population of receptors on GH cells.
在金鱼中，两种天然促性腺激素释放激素（GnRH）肽，即鲑鱼GnRH（sGnRH）和鸡II型GnRH（cGnRH-II），可刺激促性腺激素（GTH-II）和生长激素（GH）的分泌。在本研究中，我们采用了多种方法来测试sGnRH和cGnRH-II是通过不同的还是相同的GnRH受体群体作用于GTH和GH细胞的。一种GnRH拮抗剂[Ac-δ3-Pro1,4FD-Phe2,D-Trp3,6]sGnRH（类似物C）同样抑制sGnRH和cGnRH-II诱导的GTH-II释放。同样，[Ac-D(2)Nal1,4Cl-D-Phe2,D-(3)Pal3,6]cGnRH-II（类似物N）也同样抑制两种GnRH肽对GTH-II的刺激。此外，在持续存在100 nM sGnRH的情况下，100 nM脉冲的cGnRH-II未能引起额外的GTH-II释放，反之亦然。垂体片段长时间暴露于100 nM sGnRH或cGnRH-II会导致脱敏，并同等程度地降低对随后sGnRH或cGnRH-II脉冲的GTH-II反应。所有这些结果表明，sGnRH和cGnRH-II都是通过促性腺细胞上相同的GnRH受体群体起作用的。同样，（i）类似物N处理、（ii）在长时间sGnRH处理期间对cGnRH-II进行脉冲刺激（反之亦然）以及（iii）脱敏研究获得的GH反应表明，sGnRH和cGnRH-II都是通过生长激素细胞上相同的GnRH受体群体起作用的。然而，GTH-II和GH细胞上GnRH受体的特性是不同的。类似物C刺激GH释放，但不刺激GTH-II释放。相反，[Ac-δ3-Pro1,4FD-Phe2,D-Trp3,D-Arg6]mGnRH刺激GTH-II释放，但对GH释放的抑制作用较弱。这些结果表明，sGnRH和cGnRH-II作用于GTH细胞上相同的受体群体，而作用于GH细胞上功能不同的受体群体。
