Bramley T A, Stirling D, Menzies G S, Baird D T
Division of Reproductive and Developmental Sciences, University of Edinburgh Medical School, The Chancellor's Building, 49 Little France Crescent, Edinburgh EH16 4SB, Scotland, UK.
J Endocrinol. 2004 Dec;183(3):517-26. doi: 10.1677/joe.1.05918.
Scottish Blackface ewes were synchronised in mid-breeding (November; group 1; n=12 ewes) or late-breeding season (March; group 2; n=16). Anoestrous ewes (May) were treated with progestagen sponges for 7 days and then given 250 ng GnRH 3-hourly for 24 h, 2-hourly for 24 h and hourly for a further 24 h (group 3; n=12). A second group of anoestrous ewes (group 4, n=19) received three bolus injections (30 microg) of GnRH at 90-min intervals without progestagen pretreatment. After ovulation, ewes were bled twice daily until slaughter (day 4 or day 12: oestrus=day 0). Mid-breeding season (group 1) and anoestrous ewes in group 3 formed 'adequate' corpora lutea (CL) with high plasma progesterone levels (3-4 ng/ml) maintained for at least 12 days, and responded in vivo to ovine LH (oLH) (10 microg) with a rise in plasma progesterone on day 11 (group 3, but not group 1, ewes also responded on day 3). CL minces from these ewes responded to human chorionic gonadotrophin (hCG) in vitro with a dose-dependent increase in progesterone secretion. Ewes in group 4 had a foreshortened luteal phase (8-10 days) and low plasma progesterone levels (approximately 1 ng/ml), consistent with formation of inadequate CL. LH injection failed to induce a significant plasma progesterone increase. Furthermore, although progesterone secretion in vitro in response to maximally stimulating doses of hCG or dibutyryl cAMP (dbcAMP) was similar to that in adequate CL, the sensitivity of these CL to hCG (EC (effective concentration)50, 1 IU hCG/ml) was reduced 10-fold compared with adequate CL (EC50, 0.1 IU hCG/ml; P<0.01). Ewes that ovulated in the late breeding season (group 2) had high plasma progesterone, although levels began to decrease after day 10. Injection of oLH in vivo increased plasma progesterone. However, sensitivity to hCG in vitro (EC50, 0.5 IU hCG/ml) was intermediate between that of adequate luteal tissue (groups 1 and 3; EC50, 0.1 IU/ml) and that of group 4 ewes (EC50, 1 IU hCG/ml). Our data demonstrate a markedly reduced luteal sensitivity to LH in vivo and hCG in vitro in Scottish Blackface ewes with inadequate CL, and suggest that a similar loss of sensitivity to LH may occur in the late breeding season.
苏格兰黑脸母羊在繁殖中期（11月；第1组；n = 12只母羊）或繁殖后期（3月；第2组；n = 16只）进行同期发情处理。处于乏情期（5月）的母羊用孕激素海绵栓处理7天，然后每3小时注射250 ng促性腺激素释放激素（GnRH），持续24小时，之后每2小时注射一次，持续24小时，再之后每小时注射一次，持续24小时（第3组；n = 12只）。另一组乏情期母羊（第4组，n = 19只）每隔90分钟接受三次促性腺激素释放激素大剂量注射（30微克），未进行孕激素预处理。排卵后，母羊每天采血两次，直至屠宰（第4天或第12天：发情日为第0天）。繁殖中期（第1组）和第3组乏情期母羊形成了“正常”的黄体（CL），血浆孕酮水平较高（3 - 4 ng/ml），并至少维持12天，且在体内对羊促黄体生成素（oLH）（10微克）有反应，第11天血浆孕酮升高（第3组母羊在第3天也有反应，但第1组没有）。这些母羊的黄体切碎组织在体外对人绒毛膜促性腺激素（hCG）有反应，孕酮分泌呈剂量依赖性增加。第4组母羊的黄体期缩短（8 - 10天），血浆孕酮水平较低（约1 ng/ml），这与形成的黄体功能不全一致。注射促黄体生成素未能显著提高血浆孕酮水平。此外，尽管在体外，这些黄体对最大刺激剂量的hCG或二丁酰环磷腺苷（dbcAMP）的孕酮分泌反应与正常黄体相似，但与正常黄体相比，这些黄体对hCG的敏感性（有效浓度（EC）50，1 IU hCG/ml）降低了10倍（EC50，0.1 IU hCG/ml；P < 0.01）。在繁殖后期排卵的母羊（第2组）血浆孕酮水平较高，尽管在第10天后水平开始下降。体内注射羊促黄体生成素可提高血浆孕酮水平。然而，其在体外对hCG的敏感性（EC50，0.5 IU hCG/ml）介于正常黄体组织（第1组和第3组；EC50，0.1 IU/ml）和第4组母羊（EC50，1 IU hCG/ml）之间。我们的数据表明，黄体功能不全的苏格兰黑脸母羊体内对促黄体生成素和体外对hCG的敏感性显著降低，并且表明在繁殖后期可能会出现类似的对促黄体生成素敏感性丧失的情况。
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