Sakurai H, Adams B M, Adams T E
Department of Animal Science, University of California, Davis 95616, USA.
J Reprod Fertil. 1996 Nov;108(2):211-7. doi: 10.1530/jrf.0.1080211.
The effect of duration of a simulated follicular phase on gonadotrope responsiveness was assessed in orchidectomized sheep (wethers). The oestrogenic and hypothalamic inputs characteristic of the ovine follicular phase were simulated by continuous infusion of oestradiol (5 micrograms h-1 in 10% (v/v) ethanol saline) and circhoral delivery of GnRH (200 ng per hourly pulse) for 0, 6, 12, 24, 48 or 96 h (n = 6 wethers per group). Responsiveness increased (P < 0.05) with increasing duration of simulated follicular phase. In a second experiment, responsiveness was assessed 96 h after initiation of infusion of oestradiol in wethers receiving hourly pulses of GnRH or saline. Concurrent administration of GnRH reduced (P < 0.05) the magnitude of the oestradiol-induced increase in gonadotrope responsiveness. In a companion study, anterior pituitary tissue was collected 96 h after the start of infusion of oestradiol and circhoral delivery of GnRH or saline. Pituitary stores of LH and tissue concentrations of GnRH receptor and mRNA encoding the GnRH receptor were increased (P < 0.05) by oestradiol infusion. The magnitude of these oestradiol-induced responses was not affected (P > 0.05) by concurrent GnRH treatment. Tissue concentrations of FSH and mRNA encoding the FSH beta subunit were decreased (P < 0.05) by oestradiol infusion. This suppressive effect of oestradiol was not reversed by GnRH. These results indicate that oestradiol stimulation, but not concurrent delivery of GnRH, is essential for full expression of surge-like secretion of LH. In addition, the oestradiol-induced increase in gonadotrope responsiveness during the simulated follicular phase is sustained throughout the period of oestradiol delivery.
在去势绵羊（阉羊）中评估了模拟卵泡期持续时间对促性腺激素细胞反应性的影响。通过持续输注雌二醇（5微克/小时，溶于10%（v/v）乙醇盐水中）和每小时脉冲式给予促性腺激素释放激素（GnRH，200纳克/脉冲）0、6、12、24、48或96小时（每组6只阉羊），模拟绵羊卵泡期的雌激素和下丘脑输入。随着模拟卵泡期持续时间的增加，反应性增强（P<0.05）。在第二个实验中，在接受每小时一次GnRH或生理盐水脉冲的阉羊中，在开始输注雌二醇96小时后评估反应性。同时给予GnRH可降低（P<0.05）雌二醇诱导的促性腺激素细胞反应性增加的幅度。在一项配套研究中，在开始输注雌二醇和每小时脉冲式给予GnRH或生理盐水96小时后收集垂体前叶组织。输注雌二醇可增加（P<0.05）垂体促黄体生成素（LH）储备以及GnRH受体和编码GnRH受体的mRNA的组织浓度。同时给予GnRH对这些雌二醇诱导反应的幅度没有影响（P>0.05）。输注雌二醇可降低（P<0.05）促卵泡生成素（FSH）的组织浓度和编码FSHβ亚基的mRNA。GnRH不能逆转雌二醇的这种抑制作用。这些结果表明，雌二醇刺激对于LH高峰样分泌的充分表达至关重要，而同时给予GnRH并非必需。此外，在模拟卵泡期期间，雌二醇诱导的促性腺激素细胞反应性增加在整个雌二醇给药期间持续存在。
