Knight P G, Feist S A, Tannetta D S, Bleach E C, Fowler P A, O'Brien M, Groome N P
School of Animal and Microbial Sciences, University of Reading, Whiteknights, UK.
J Reprod Fertil. 1998 May;113(1):159-66. doi: 10.1530/jrf.0.1130159.
A new two-site ELISA was validated for ovine plasma and used to measure circulating inhibin-A concentrations during a synchronized oestrous cycle in four ewes and throughout pregnancy in six ewes. Inhibin A concentrations were also determined in four ewes during chronic treatment with a GnRH agonist and after subsequent exposure to pregnant mares' serum gonadotrophin (PMSG) to stimulate ovarian follicular development. Concentrations of FSH, LH, oestradiol and progesterone were determined by radioimmunoassay. The detection limit of the inhibin-A ELISA was approximately 50 pg ml-1 and no significant crossreaction was observed with a range of related molecules including activin-A, inhibin-B, activin-B, follistatin and alpha 2-macroglobulin. Inhibin-A concentrations were below the detection limit in plasma from hypophysectomized and ovariectomized ewes. During the oestrous cycle, plasma inhibin-A concentrations (approximately 0.3-0.4 ng ml-1) did not vary during the follicular phase whereas plasma oestradiol increased approximately tenfold. After the preovulatory LH/FSH surge, inhibin-A fell to a nadir (approximately 0.15 ng ml-1) coincident with the peak of the postovulatory FSH rise. During the next 2 days, FSH concentrations fell to basal values as inhibin-A concentrations increased (P < 0.05) to a peak (approximately 0.5 ng ml-1) 3 days after the preovulatory LH/FSH surge. Over the following 3 days, FSH values increased again (P < 0.05) as inhibin-A concentrations fell to approximately 0.25 ng ml-1 (P < 0.05). Chronic GnRH agonist treatment suppressed FSH concentrations by about 50%, while inhibin-A and oestradiol concentrations fell below detection limits. Within 2 days after the PMSG injection, concentrations of inhibin-A (approximately 4.5 ng ml-1) and oestradiol (approximately 20 pg ml-1) had increased to very high values, while FSH concentrations had been reduced by a further 50%. Plasma concentrations of inhibin-A and FSH were similar to those in nonpregnant ewes during the first 60 days of gestation, but inhibin-A values fell markedly (sevenfold; P < 0.01) between days 60 and 90, coincident with a twofold decrease in FSH (P < 0.05). Inhibin A and FSH concentrations remained low for the remainder of gestation and were positively correlated throughout pregnancy (r = 0.48; P < 0.005). These observations support an endocrine feedback role for ovarian inhibin-A and oestradiol in controlling the secondary (postovulatory) FSH surge in ewes, but indicate that an increase in oestradiol is responsible for the characteristic reduction in FSH during the early to mid-follicular phase. The reduced secretion of FSH from mid- to late pregnancy cannot be attributed to increased inhibin-A secretion by the feto-placental unit, but most likely reflects increased steroid secretion from this source.
一种新的双位点酶联免疫吸附测定法（ELISA）在绵羊血浆中得到验证，并用于测量4只母羊同步发情周期和6只母羊整个妊娠期循环中的抑制素A浓度。还测定了4只母羊在长期使用促性腺激素释放激素（GnRH）激动剂治疗期间以及随后暴露于孕马血清促性腺激素（PMSG）以刺激卵巢卵泡发育后的抑制素A浓度。促卵泡生成素（FSH）、促黄体生成素（LH）、雌二醇和孕酮的浓度通过放射免疫测定法测定。抑制素A ELISA的检测限约为50 pg/ml-1，并且在一系列相关分子（包括激活素A、抑制素B、激活素B、卵泡抑素和α2-巨球蛋白）中未观察到明显的交叉反应。在垂体切除和卵巢切除的母羊血浆中，抑制素A浓度低于检测限。在发情周期中，卵泡期血浆抑制素A浓度（约0.3 - 0.4 ng/ml-1）没有变化，而血浆雌二醇增加了约10倍。在排卵前LH/FSH高峰后，抑制素A降至最低点（约0.15 ng/ml-1），与排卵后FSH升高的峰值同时出现。在接下来的2天内，随着抑制素A浓度增加（P < 0.05）至排卵前LH/FSH高峰后3天的峰值（约0.5 ng/ml-1），FSH浓度降至基础值。在接下来的3天内，随着抑制素A浓度降至约0.25 ng/ml-1（P < 0.05），FSH值再次升高（P < 0.05）。长期GnRH激动剂治疗使FSH浓度降低约50%，而抑制素A和雌二醇浓度降至检测限以下。在注射PMSG后2天内，抑制素A浓度（约4.5 ng/ml-1）和雌二醇浓度（约20 pg/ml-1）升高至非常高的值，而FSH浓度又降低了50%。妊娠前60天血浆中抑制素A和FSH的浓度与未怀孕母羊相似，但在第60天至第90天之间，抑制素A值显著下降（7倍；P < 0.01），同时FSH下降了两倍（P < 0.05）。在妊娠剩余时间内，抑制素A和FSH浓度保持较低水平，并且在整个妊娠期呈正相关（r = 0.48；P < 0.005）。这些观察结果支持卵巢抑制素A和雌二醇在控制母羊排卵后FSH二次高峰方面的内分泌反馈作用，但表明雌二醇的增加是卵泡早期至中期FSH特征性降低的原因。妊娠中期至晚期FSH分泌减少不能归因于胎儿 - 胎盘单位抑制素A分泌增加，而很可能反映了该来源类固醇分泌增加。
