Joseph I B, Currie W D, Rawlings N C
Department of Veterinary Physiological Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada.
J Reprod Fertil. 1992 Mar;94(2):511-23. doi: 10.1530/jrf.0.0940511.
During the breeding season, five groups of three ewes were implanted at ovariectomy with 0.36, 0.5, 1.0 and 6.0 cm oestradiol implants or implants containing no steroid. Eleven days after receiving implants, blood samples were taken every 10 min for 6 h; implants were then removed. Treatments were repeated three times during each of two consecutive breeding seasons and four times during the intervening anoestrus. In ovariectomized ewes without steroid treatment, luteinizing hormone (LH) pulse frequency increased from early to mid-breeding season, decreased to a minimum at mid-anoestrus and increased to reach a maximum at the mid-point of the second breeding season, subsequently declining. LH pulse amplitude was inversely related to frequency. Basal serum LH concentrations decreased gradually from the first breeding season to reach a minimum at mid-anoestrus and gradually increased to reach a maximum at the end of the second breeding season. Mean serum LH and follicle-stimulating hormone (FSH) concentrations were higher at the end of the second breeding season compared with the beginning of the first breeding season. All parameters of gonadotrophin secretion were decreased much more by oestradiol during the anoestrus than during the breeding season. LH pulse frequency was decreased during anoestrus and at high oestradiol concentrations during the first breeding season. Apart from LH pulse amplitude, the decreases in all parameters of gonadotrophin secretion were less during the second compared with the first breeding season. The minimum effective dose of oestradiol required to decrease mean and basal serum concentrations of LH during anoestrus was lower than in the breeding season. The minimum effective dose of oestradiol required to decrease mean serum concentrations of FSH was lower in the first compared with the second breeding season. Oestradiol depression of LH pulse amplitude and mean serum concentrations of LH and FSH showed a dose dependency during the breeding season. During anoestrus dose dependency was seen for basal concentrations of LH and mean serum concentrations of LH and FSH. We conclude that significant chronic changes in gonadotrophin secretion occur in the ewe with time after ovariectomy. Sensitivity to oestradiol also changes, and the effects of oestradiol are not always dose dependent. We suggest that the circannual pattern of LH pulse frequency and basal LH secretion are directly linked to the circannual cycle of photoperiod.(ABSTRACT TRUNCATED AT 400 WORDS)
在繁殖季节，将五组每组三只母羊进行卵巢切除术后，分别植入0.36、0.5、1.0和6.0厘米的雌二醇植入物或不含类固醇的植入物。植入后11天，每10分钟采集一次血样，共采集6小时；然后取出植入物。在连续两个繁殖季节中的每个季节重复进行三次处理，在其间的乏情期重复进行四次处理。在未经类固醇处理的去卵巢母羊中，促黄体生成素（LH）脉冲频率从繁殖季节早期到中期增加，在乏情期中期降至最低，在第二个繁殖季节中期增至最高，随后下降。LH脉冲幅度与频率呈负相关。基础血清LH浓度从第一个繁殖季节开始逐渐降低，在乏情期中期降至最低，然后逐渐升高，在第二个繁殖季节结束时达到最高。与第一个繁殖季节开始时相比，第二个繁殖季节结束时血清LH和促卵泡生成素（FSH）的平均浓度更高。与繁殖季节相比，乏情期雌二醇对促性腺激素分泌的所有参数的抑制作用更大。在乏情期以及第一个繁殖季节高雌二醇浓度时，LH脉冲频率降低。与第一个繁殖季节相比，第二个繁殖季节促性腺激素分泌所有参数的降低幅度较小，但LH脉冲幅度除外。在乏情期降低LH平均和基础血清浓度所需的雌二醇最小有效剂量低于繁殖季节。与第二个繁殖季节相比，第一个繁殖季节降低FSH平均血清浓度所需的雌二醇最小有效剂量更低。在繁殖季节，雌二醇对LH脉冲幅度以及LH和FSH平均血清浓度的抑制作用呈剂量依赖性。在乏情期，对LH基础浓度以及LH和FSH平均血清浓度呈剂量依赖性。我们得出结论，去卵巢母羊促性腺激素分泌随时间发生显著的慢性变化。对雌二醇的敏感性也发生变化，且雌二醇的作用并非总是剂量依赖性的。我们认为，LH脉冲频率和基础LH分泌的年周期模式与光周期的年周期直接相关。（摘要截取自400字）
