Moenter S M, Caraty A, Karsch F J
Reproductive Sciences Program, University of Michigan, Ann Arbor 48109-0404.
Endocrinology. 1990 Sep;127(3):1375-84. doi: 10.1210/endo-127-3-1375.
Previous studies suggest two roles for estradiol in inducing the LH surge in ewes: a neural action to evoke a sudden release of GnRH and a pituitary action to maximize response to GnRH. We tested two hypotheses: a follicular phase estradiol rise induces a GnRH surge; and the surge-inducing action of estradiol does not vary with season. In the breeding season, ewes in the midluteal phase of the estrous cycle were ovariectomized and treated with implants producing luteal phase levels of estradiol and progesterone, and an apparatus was surgically installed for later sampling of pituitary portal blood. At the normal time of luteolysis (1 week later), progesterone implants were removed, simulating luteal regression. Ewes were divided into two groups: estradiol implants also removed (n = 6) and estradiol implants added 16 h after progesterone removal to produce a rise in estradiol to levels that mimic those that circulate in the late follicular phase (n = 6). In anestrus, the estradiol rise treatment was replicated in ewes (n = 5) after an artificial luteal phase produced by sequential insertion and subsequent removal of progesterone implants. Regardless of season, the LH surge induced by estradiol was invariably accompanied by a massive GnRH surge, ranging from 73- to 394-fold over presurge values. The GnRH and LH surges began together, but the GnRH surge continued well beyond the surge of LH. There was no seasonal difference in time course or amplitude of the GnRH surge. Control ewes not treated with estradiol exhibited regular pulses of LH and GnRH every 1-2 h, but no surge of either hormone. We conclude that, regardless of season, a rise in estradiol to late follicular phase levels initiates a large and abrupt GnRH surge coincident with the onset of the LH surge. The LH surge ends despite continued elevation of GnRH.
先前的研究表明，雌二醇在诱导母羊促黄体生成素（LH）峰方面有两种作用：一种是神经作用，引发促性腺激素释放激素（GnRH）的突然释放；另一种是垂体作用，使对GnRH的反应最大化。我们测试了两个假设：卵泡期雌二醇升高会诱导GnRH峰；雌二醇诱导峰的作用不随季节变化。在繁殖季节，处于发情周期黄体中期的母羊接受卵巢切除术，并植入能产生黄体期水平雌二醇和孕酮的装置，同时通过手术安装一个装置以便随后采集垂体门脉血。在正常黄体溶解时间（1周后），移除孕酮植入物，模拟黄体退化。母羊被分为两组：也移除雌二醇植入物的组（n = 6）和在移除孕酮16小时后添加雌二醇植入物以使雌二醇升高至模拟卵泡晚期循环水平的组（n = 6）。在乏情期，通过依次插入和随后移除孕酮植入物产生人工黄体期后，对母羊（n = 5）重复进行雌二醇升高处理。无论季节如何，雌二醇诱导的LH峰总是伴随着GnRH的大量释放，比释放前的值高出73至394倍。GnRH峰和LH峰同时开始，但GnRH峰在LH峰之后仍持续很长时间。GnRH峰的时间进程或幅度没有季节性差异。未用雌二醇处理的对照母羊每1 - 2小时有规律地脉冲式释放LH和GnRH，但没有出现任何一种激素的峰。我们得出结论，无论季节如何，雌二醇升高至卵泡晚期水平会引发与LH峰开始同时出现的大量且突然的GnRH峰。尽管GnRH持续升高，LH峰仍会结束。
