Henderson Helen L, Hodson David J, Gregory Susan J, Townsend Julie, Tortonese Domingo J
Department of Anatomy, University of Bristol, Bristol BS2 8EJ, United Kingdom.
Biol Reprod. 2008 Feb;78(2):370-7. doi: 10.1095/biolreprod.107.064063. Epub 2007 Dec 19.
Previous studies have provided evidence for a paracrine interaction between pituitary gonadotrophs and lactotrophs. Here, we show that GnRH is able to stimulate prolactin (PRL) release in ovine primary pituitary cultures. This effect was observed during the breeding season (BS), but not during the nonbreeding season (NBS), and was abolished by the application of bromocriptine, a specific dopamine agonist. Interestingly, GnRH gained the ability to stimulate PRL release in NBS cultures following treatment with bromocriptine. In contrast, thyrotropin-releasing hormone, a potent secretagogue of PRL, stimulated PRL release during both the BS and NBS and significantly enhanced the PRL response to GnRH during the BS. These results provide evidence for a photoperiodically modulated functional interaction between the GnRH/gonadotropic and prolactin axes in the pituitary gland of a short day breeder. Moreover, the stimulation of PRL release by GnRH was shown not to be mediated by the gonadotropins, since immunocytochemical, Western blotting, and PCR studies failed to detect pituitary LH or FSH receptor protein and mRNA expressions. Similarly, no gonadotropin receptor expression was observed in the pituitary gland of the horse, a long day breeder. In contrast, S100 protein, a marker of folliculostellate cells, which are known to participate in paracrine mechanisms within this tissue, was detected throughout the pituitaries of both these seasonal breeders. Therefore, an alternative gonadotroph secretory product, a direct effect of GnRH on the lactotroph, or another cell type, such as the folliculostellate cell, may be involved in the PRL response to GnRH in these species.
以往的研究已为垂体促性腺细胞与催乳细胞之间的旁分泌相互作用提供了证据。在此，我们表明促性腺激素释放激素（GnRH）能够刺激绵羊原代垂体培养物中催乳素（PRL）的释放。在繁殖季节（BS）观察到了这种效应，但在非繁殖季节（NBS）未观察到，并且应用溴隐亭（一种特异性多巴胺激动剂）后这种效应被消除。有趣的是，在用溴隐亭处理后，GnRH在NBS培养物中获得了刺激PRL释放的能力。相比之下，促甲状腺激素释放激素（一种有效的PRL促分泌素）在BS和NBS期间均刺激PRL释放，并在BS期间显著增强了PRL对GnRH的反应。这些结果为短日照繁殖动物垂体中GnRH/促性腺激素和催乳素轴之间的光周期调节功能相互作用提供了证据。此外，GnRH对PRL释放的刺激作用并非由促性腺激素介导，因为免疫细胞化学、蛋白质印迹和PCR研究未能检测到垂体促黄体生成素（LH）或促卵泡生成素（FSH）受体蛋白及mRNA表达。同样，在长日照繁殖动物马的垂体中未观察到促性腺激素受体表达。相比之下，S100蛋白（一种已知参与该组织内旁分泌机制的滤泡星状细胞标志物）在这两种季节性繁殖动物的整个垂体中均被检测到。因此，促性腺细胞的另一种分泌产物、GnRH对催乳细胞的直接作用或另一种细胞类型（如滤泡星状细胞）可能参与了这些物种中PRL对GnRH的反应。
