Foster D L
Endocrinology. 1984 Sep;115(3):1186-9. doi: 10.1210/endo-115-3-1186.
The sensitivity of the LH surge mechanism to estradiol-positive feedback was examined in immature lambs (19 weeks of age) several weeks before first ovulation (31 weeks of age). To minimize differences in basal estradiol concentrations, lambs were pretreated with a low level of estradiol (2 pg/ml; Silastic capsule) for 4 days and were ovariectomized before they were challenged with one of five levels of estradiol (n = 5 lambs/level). The estradiol increments produced after insertion of the second set of estradiol implants ranged from 2-11 pg/ml. All estradiol increments, even those as low as 2 pg/ml, produced LH surges; in the absence of an estradiol increment (second implant not inserted; n = 5 lambs), a LH surge did not occur. The similarity of the dose-response curve for estradiol-induced LH release in the lamb to that which we previously reported for the mature female indicates that the lamb is equally sensitive to estradiol stimulatory feedback action long before the age of first ovulation. This suggests that low estradiol secretion, rather than reduced sensitivity of the surge mechanism to estradiol-positive feedback, is responsible for the anovulatory condition of the immature female sheep.
在首次排卵（31周龄）前几周，对未成熟羔羊（19周龄）促黄体生成素峰机制对雌二醇正反馈的敏感性进行了研究。为尽量减少基础雌二醇浓度的差异，给羔羊用低水平雌二醇（2 pg/ml；硅橡胶胶囊）预处理4天，并在对其用五个水平的雌二醇之一进行刺激前进行卵巢切除（每个水平n = 5只羔羊）。插入第二组雌二醇植入物后产生的雌二醇增量范围为2 - 11 pg/ml。所有雌二醇增量，即使低至2 pg/ml，均产生促黄体生成素峰；在没有雌二醇增量的情况下（未插入第二个植入物；n = 5只羔羊），未出现促黄体生成素峰。羔羊中雌二醇诱导促黄体生成素释放的剂量反应曲线与我们之前报道的成年雌性的相似，这表明在首次排卵年龄之前很久，羔羊对雌二醇刺激反馈作用同样敏感。这表明低雌二醇分泌而非促黄体生成素峰机制对雌二醇正反馈的敏感性降低是未成熟母羊无排卵状态的原因。
