Turzillo A M, Campion C E, Clay C M, Nett T M
Animal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins 80523.
Endocrinology. 1994 Oct;135(4):1353-8. doi: 10.1210/endo.135.4.7925096.
Estradiol increases the number of GnRH receptors in the ewe. Although results from studies conducted in vitro indicate that progesterone may have a negative influence on the number of ovine GnRH receptors, this effect of progesterone has not been documented in vivo. To explore the regulation of GnRH receptors at the level of gene expression, a partial complementary DNA (cDNA) encoding ovine GnRH receptor was isolated using reverse transcription and polymerase chain reaction methodology. This partial cDNA (701 basepairs) was used to isolate a full-length cDNA encoding GnRH receptor from an ovine pituitary cDNA library. Northern blot analysis of RNA from ovine pituitary glands using the partial cDNA as a molecular probe revealed four messenger RNA (mRNA) transcripts at 5.6, 3.8, 2.1, and 1.3 kilobases. In some samples, a fifth transcript at 0.8 kilobases was also evident. GnRH receptor mRNA was not detected in ovine brain, heart, kidney, adrenal, or liver tissues. To examine the regulation of GnRH receptor mRNA and GnRH receptors during the early preovulatory period, relationships among steady state concentrations of GnRH receptor mRNA, numbers of GnRH receptors, and circulating concentrations of progesterone and estradiol during luteolysis were characterized. We hypothesized that during luteolysis, decreased concentrations of progesterone would be associated with increased concentrations of GnRH receptor mRNA and increased numbers of GnRH receptors. On day 11 or 12 of the estrous cycle, luteolysis was induced in 14 ewes by treatment with prostaglandin F2 alpha (PGF2 alpha). Four ewes were treated with saline (saline controls). Anterior pituitary tissue was collected 4 h (n = 4), 12 h (n = 5), and 24 h (n = 5) after treatment with PGF2 alpha or 24 h after treatment with saline and from four untreated ewes on day 11 or 12 of the estrous cycle (untreated controls). Twelve hours after treatment with PGF2 alpha, circulating concentrations of progesterone had decreased (P < 0.05) to 46% of the control values; however, concentrations of estradiol were not different from those in control ewes. Concentrations of GnRH receptor mRNA increased 2-fold during luteolysis and were higher than control values 12 h after PGF2 alpha treatment (P < 0.05). This increase in GnRH receptor mRNA was not accompanied by an increase in the number of GnRH receptors. Twenty-four hours after treatment with PGF2 alpha, concentrations of progesterone in PGF2 alpha-treated ewes had decreased (P < 0.05) to 15% of control values, whereas concentrations of estradiol had increased (P < 0.05) to 321% of control values.(ABSTRACT TRUNCATED AT 400 WORDS)
雌二醇可增加母羊体内促性腺激素释放激素（GnRH）受体的数量。尽管体外研究结果表明，孕酮可能对绵羊GnRH受体数量产生负面影响，但这种孕酮效应尚未在体内得到证实。为了在基因表达水平上探究GnRH受体的调控机制，采用逆转录和聚合酶链反应方法分离出了一段编码绵羊GnRH受体的部分互补DNA（cDNA）。利用该部分cDNA（701个碱基对）从绵羊垂体cDNA文库中分离出了编码GnRH受体的全长cDNA。以该部分cDNA作为分子探针，对绵羊垂体RNA进行Northern印迹分析，结果显示有4种信使RNA（mRNA）转录本，大小分别为5.6、3.8、2.1和1.3千碱基。在一些样本中，还明显存在一个0.8千碱基的第五种转录本。在绵羊的脑、心脏、肾脏、肾上腺或肝脏组织中未检测到GnRH受体mRNA。为了研究排卵前期早期GnRH受体mRNA和GnRH受体的调控情况，对黄体溶解期间GnRH受体mRNA的稳态浓度、GnRH受体数量以及孕酮和雌二醇的循环浓度之间的关系进行了表征。我们假设在黄体溶解过程中，孕酮浓度降低会伴随着GnRH受体mRNA浓度升高以及GnRH受体数量增加。在发情周期的第11天或第12天，用前列腺素F2α（PGF2α）处理14只母羊以诱导黄体溶解。4只母羊用生理盐水处理（生理盐水对照组）。在PGF2α处理后4小时（n = 4）、12小时（n = 5）和24小时（n = 5），或生理盐水处理后24小时，以及在发情周期第11天或第12天从4只未处理的母羊（未处理对照组）采集垂体前叶组织。PGF2α处理12小时后，孕酮的循环浓度降低（P < 0.05）至对照值的46%；然而，雌二醇浓度与对照母羊无差异。黄体溶解期间GnRH受体mRNA浓度增加了2倍，且在PGF2α处理12小时后高于对照值（P < 0.05）。GnRH受体mRNA的这种增加并未伴随着GnRH受体数量的增加。PGF2α处理24小时后，PGF2α处理母羊的孕酮浓度降低（P < 0.05）至对照值的15%，而雌二醇浓度增加（P < 0.05）至对照值的321%。（摘要截取自400字）
