Land R B, Carr W R, Thompson R
J Reprod Fertil. 1979 May;56(1):243-8. doi: 10.1530/jrf.0.0560243.
The influence of breed and season on the sensitivity of the pituitary gland of sheep to LH-RH was assessed. Ovariectomized ewes of 3 breeds (Finnish Landrace, Scottish Blackface and Tasmanian Merino) with differing normal breeding seasons and with differing ovulation rates were injected (i.v.) with 3 doses of LH-RH (1.56, 6.25 or 25.0 micrograms) at 3 different times of the year covering the anoestrous and the breeding seasons of intact ewes; 9 ewes of each breed (3 per sub-class) were examined on the first and third occasions, 6 (2 per sub-class) on the second. The response was measured in terms of the concentration of LH in peripheral plasma 20, 40, 60 and 80 min after injection. Time of year, but not the breed of sheep, affected the magnitude of the response; the data indicated that the duration of LH secretion was greater during the breeding season than during anoestrus. It was concluded that changes in the spontaneous activity of the hypothalamus/hypophysis could contribute to seasonal changes in LH secretion independently of the modifying effects of gonadal steroids. Such variation in unmodulated activity apparently does not contribute to the differences in ovulation rate among the 3 breeds.
评估了品种和季节对绵羊垂体对促黄体生成素释放激素（LH - RH）敏感性的影响。选用3个品种（芬兰长白、苏格兰黑脸和塔斯马尼亚美利奴）的去卵巢母羊，它们具有不同的正常繁殖季节和排卵率，在一年中涵盖未发情期和完整母羊繁殖季节的3个不同时间静脉注射3种剂量的LH - RH（1.56、6.25或25.0微克）；每个品种9只母羊（每个亚类3只）在第一次和第三次检查，6只（每个亚类2只）在第二次检查。根据注射后20、40、60和80分钟外周血浆中LH的浓度来衡量反应。一年中的时间而非绵羊品种影响反应的大小；数据表明繁殖季节LH分泌的持续时间比乏情期更长。得出的结论是，下丘脑/垂体自发活动的变化可独立于性腺类固醇的调节作用而导致LH分泌的季节性变化。这种未调制活动的变化显然不会导致这3个品种之间排卵率的差异。
