Evidence that gonadotropin-releasing hormone stimulates gene expression and levels of active nitric oxide synthase type I in pituitary gonadotrophs, a process altered by desensitization and, indirectly, by gonadal steroids
Evidence that gonadotropin-releasing hormone stimulates gene expression and levels of active nitric oxide synthase type I in pituitary gonadotrophs, a process altered by desensitization and, indirectly, by gonadal steroids
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DOI：
10.1210/en.139.4.2163
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发表时间：
1998-04-01
期刊：
影响因子：
4.8
通讯作者：
Counis, R
中科院分区：
文献类型：
--
作者：
Garrel, G;Lerrant, Y;Counis, R
为了确定性腺激素对存在于促性腺细胞和卵泡星状细胞中的垂体型一氧化氮合酶I （NOS I）的作用部位和机制，在GnRH拮抗剂（Antarelix）存在的情况下，在雄性大鼠中研究了去势和类固醇的作用。Western分析显示，随着时间的推移，切除兰花后，NOS I蛋白的浓度迅速而显著地增加，在24小时内增加一倍，在3-7天后达到最大的4- b倍，随后在2周后逐渐下降。睾酮或雌二醇替代，或施用GnRH拮抗剂，完全消除了阉割的影响，表明通过GnRH介导类固醇效应。在未阉割的大鼠中，类固醇和GnRH拮抗剂也导致NOS I水平降低（50-60%），与抑制内源性GnRH刺激一致。与此形成鲜明对比的是，给未受GnRH影响的大鼠服用强效GnRH激动剂（triprelin）会增加NOS I的水平。一项使用长效制剂的时间过程研究表明，NOS I的上升在大约5小时后迅速发展，8小时后可检测到2倍的增长，48小时后最大增长4.5倍。随后水平下降，其方式与GnRH持续存在时可能发生的同源脱敏一致；然而，与促性腺激素释放相比，其特征不同且延迟。对于NOS I蛋白，去势或GnRH激动剂使NOS I信使RNA浓度升高，类固醇或GnRH拮抗剂使NOS I信使RNA浓度降低。综上所述，这些数据表明，类固醇通过下丘脑调节GnRH间接调节NOS I信使RNA和蛋白质水平，GnRH是NOS I的主要调节因子。NADPH-diaphorase erase组织化学结合细胞的免疫鉴定显示，影响NOS I浓度的处理同时改变了其活性，但仅在促性腺细胞中改变，而在滤泡星状细胞（对GnRH无反应）中不改变，强化了GnRH起主要调节作用的观点。促性腺激素中gnrh依赖性NOS I的表达和随之而来的一氧化氮的产生代表了垂体前叶神经肽的一种潜在的新信号通路，与先前报道的gnrh诱导的cGMP产生一致，其作用仍有待评估。
To determine the site and mechanism of action of gonadal steroids on pituitary nitric oxide synthase type I (NOS I), present in both gonadotrophs and folliculo-stellate cells, the effects of castration and steroids were examined in male rats, in the presence of a GnRH antagonist (Antarelix). Western analysis showed a rapid and substantial increase with time, after orchidectomy, of NOS I protein, the concentration doubling in 24 h and reaching a maximal 4- to B-fold increase after 3-7 days, followed by a progressive decline after 2 weeks. Testosterone or estradiol replacement, or administration of GnRH antagonist, totally abolished the effects of castration, demonstrating a mediation of the steroid effects via GnRH. In noncastrated rats, steroids and the GnRH antagonist also caused a reduction in the levels of NOS I (by 50-60%), consistent with inhibition of endogenous GnRH stimulation. In marked contrast, administration of a potent GnRH agonist (Triptorelin) to intact rats increased the levels of NOS I. A time-course study with a long-lasting formulation showed that rise in NOS I developed rapidly after a lag of approximately 5 h, with a 2-fold increase detectable after 8 h and a maximal 4.5-fold after 48 h. The level declined afterwards in a manner consistent with homologous desensitization that may occur in the continuous presence of GnRH; however, the profile was different and delayed compared with those of gonadotropin release. As observed for NOS I protein, NOS I messenger RNA concentration was increased by castration or GnRH agonist and reduced by steroids or GnRH antagonist. Taken together, these data demonstrate that steroids indirectly regulate NOS I messenger RNA and protein levels, through the hypothalamic modulation of GnRH, which represents the primary regulator of NOS I. No effect of steroids on NOS I was seen in the posterior lobe. NADPH-diaphorase erase histochemistry coupled to immuno-identification of the cells revealed that the treatments affecting the concentration of NOS I concomitantly altered the activity but exclusively in gonadotrophs and not in folliculo-stellate cells (which do not respond to GnRH), reinforcing the idea that GnRH played a major regulatory role. Expression in gonadotrophs of a GnRH-dependent NOS I and the ensuing-production of nitric oxide represents a potentially novel signaling pathway for the neuropeptide in the anterior pituitary, consistent with the previously reported GnRH-induced cGMP production, the role of which remains to be evaluated.