Yasin M, Dalkin A C, Haisenleder D J, Kerrigan J R, Marshall J C
Department of Internal Medicine, University of Virginia Health Science Center, Charlottesville 22908.
Endocrinology. 1995 Apr;136(4):1559-64. doi: 10.1210/endo.136.4.7895666.
GnRH acts via a single cell surface receptor (GnRH-R), and the number of pituitary GnRH-R increases on proestrus, after gonadectomy, or in response to pulsatile GnRH in the rat. Estradiol (E2) is known to exert a transient positive action to increase GnRH-R number, and the rise in plasma E2 contributes to initiation of the midcycle LH surge. The present study was designed to determine the effect of GnRH pulse amplitude and frequency on GnRH-R messenger RNA (mRNA) levels and to assess the relative contributions of GnRH and gonadal steroids to increasing GnRH-R gene expression. These studies were conducted in vivo using previously characterized GnRH-deficient male (castrate testosterone-replaced) and ovariectomized phenoxybenzamine-treated female models. To investigate the effect of GnRH pulse amplitude, adult male and female rats received GnRH iv (5-250 ng/pulse at 30-min intervals; saline pulses to controls) for 12 or 24 h. In males, GnRH-R mRNA was increased by all pulse doses, with maximal effects (3-fold) at 5-25 ng/pulse. In contrast, only lower doses (5-10 ng/pulse) were effective in females (2-fold increase). In a subsequent study, GnRH pulses (25 ng for males; 10 ng for females) were given at 8-, 30-, or 240-min intervals for 12 or 24 h. Some animals received a continuous GnRH infusion (200 ng/h). In males, GnRH-R mRNA levels were stimulated by all GnRH pulse intervals (maximal after 30-min pulses), whereas continuous GnRH was ineffective. In females, only 30- and 240-min pulse intervals increased GnRH-R mRNA levels, with faster (8-min) pulses or continuous GnRH being ineffective. To determine the relative roles of ovarian steroids and GnRH, ovariectomized phenoxybenzamine-treated female animals received GnRH (10 ng/pulse, 30-min interval), E2 (via sc implants; plasma E2 levels, approximately 50 pg/ml), or their combination for 12-24 h (saline pulses to controls). In the absence of E2, GnRH-R concentrations fell by 70% between 12-24 h. E2 alone tended to increase GnRH-R mRNA at 12 h, with a 2-fold rise observed after 24 h. Pulsatile GnRH alone increased GnRH-R mRNA by 50% at 12 h (compared to saline-pulsed controls; P < 0.05) and by 6-fold after 24 h. When GnRH and E2 were combined, the magnitude of the increase (vs. saline controls) was greater than that seen for either GnRH or E2 alone.(ABSTRACT TRUNCATED AT 400 WORDS)
促性腺激素释放激素（GnRH）通过单一的细胞表面受体（GnRH-R）发挥作用，在大鼠发情前期、性腺切除后或对脉冲式GnRH作出反应时，垂体GnRH-R的数量会增加。已知雌二醇（E2）会产生短暂的正向作用以增加GnRH-R的数量，血浆E2的升高有助于引发月经周期中期促黄体生成素（LH）高峰。本研究旨在确定GnRH脉冲幅度和频率对GnRH-R信使核糖核酸（mRNA）水平的影响，并评估GnRH和性腺类固醇在增加GnRH-R基因表达方面的相对作用。这些研究在体内进行，使用先前已表征的GnRH缺乏雄性（阉割后补充睾酮）和经苯氧苄胺处理的卵巢切除雌性模型。为了研究GnRH脉冲幅度的影响，成年雄性和雌性大鼠静脉注射GnRH（每隔30分钟注射5 - 250纳克/脉冲；给对照组注射生理盐水脉冲），持续12或24小时。在雄性中，所有脉冲剂量均可使GnRH-R mRNA增加，在5 - 25纳克/脉冲时效果最佳（增加3倍）。相比之下，在雌性中只有较低剂量（5 - 10纳克/脉冲）有效（增加2倍）。在随后的研究中，每隔8、30或240分钟给予GnRH脉冲（雄性为25纳克；雌性为10纳克），持续12或24小时。一些动物接受持续GnRH输注（200纳克/小时）。在雄性中，所有GnRH脉冲间隔均可刺激GnRH-R mRNA水平（30分钟脉冲后达到最大值），而持续GnRH则无效。在雌性中，只有30分钟和240分钟的脉冲间隔可增加GnRH-R mRNA水平，较快（8分钟）的脉冲或持续GnRH无效。为了确定卵巢类固醇和GnRH的相对作用，经苯氧苄胺处理的卵巢切除雌性动物接受GnRH（10纳克/脉冲，间隔30分钟）、E2（通过皮下植入；血浆E2水平约为50皮克/毫升）或它们的组合，持续12 - 24小时（给对照组注射生理盐水脉冲）。在没有E2的情况下，12 - 24小时内GnRH-R浓度下降70%。单独使用E2在12小时时倾向于增加GnRH-R mRNA，24小时后观察到增加2倍。单独的脉冲式GnRH在12小时时使GnRH-R mRNA增加50%（与生理盐水脉冲对照组相比；P < 0.05），24小时后增加6倍。当GnRH和E2联合使用时，增加的幅度（与生理盐水对照组相比）大于单独使用GnRH或E2时。（摘要截短至400字）
