Webster J R, Moenter S M, Barrell G K, Lehman M N, Karsch F J
Reproductive Sciences Program, University of Michigan, Ann Arbor 48109-0404.
Endocrinology. 1991 Sep;129(3):1635-43. doi: 10.1210/endo-129-3-1635.
Previous studies demonstrated that the thyroid gland is required for the changes in LH secretion that lead to the end of the breeding season of female sheep, a reproductive transition generated within the ewe by an endogenous annual rhythm. The present study tested the hypothesis that this role of the thyroid is mediated via the GnRH neurosecretory system. The pulsatile secretion of GnRH into hypophyseal portal blood and LH into peripheral blood, as well as the neuroanatomical distribution of GnRH neurons and their light microscopic morphology, were compared among anestrous ewes and thyroidectomized (THX) ewes that failed to make the transition to the anestrous season. The study was conducted under photoperiodic conditions in which the transition to anestrus was generated by the endogenous rhythm. Each animal was ovariectomized and treated sc with a constant release implant of estradiol to normalize gonadal steroid status among thyroid-intact and THX ewes. High frequency pulses of GnRH and LH were evident in THX ewes that failed to make the transition to anestrus, whereas pulsatile secretion of GnRH and LH was generally not observed in thyroid-intact controls that had entered anestrus. This marked effect of thyroidectomy on GnRH secretion was not associated with widespread changes in the total number, distribution, or light microscopic morphology of GnRH neurons in the hypothalamus and preoptic area. Our finding that pulsatile secretion of GnRH is elevated in THX ewes that fail to make the transition to anestrus supports the hypothesis that the thyroid gland is required for the endogenously generated switch in function of the GnRH neurosecretory system that leads to the end of the breeding season of the ewe.
先前的研究表明，甲状腺对于促黄体生成素（LH）分泌的变化是必需的，这种变化会导致母羊繁殖季节的结束，这是一种由内源性年度节律在母羊体内产生的生殖转变。本研究检验了这样一个假说，即甲状腺的这一作用是通过促性腺激素释放激素（GnRH）神经分泌系统介导的。比较了处于乏情期的母羊和未能进入乏情季节的甲状腺切除（THX）母羊中，GnRH向垂体门脉血的脉冲式分泌以及LH向外周血的脉冲式分泌，以及GnRH神经元的神经解剖分布及其光学显微镜形态。该研究是在光周期条件下进行的，其中向乏情期的转变是由内源性节律产生的。每只动物都进行了卵巢切除，并皮下植入了持续释放的雌二醇以使甲状腺完整和THX母羊的性腺类固醇状态正常化。在未能进入乏情期的THX母羊中，GnRH和LH的高频脉冲很明显，而在已进入乏情期的甲状腺完整的对照组中，通常未观察到GnRH和LH的脉冲式分泌。甲状腺切除对GnRH分泌的这种显著影响与下丘脑和视前区GnRH神经元的总数、分布或光学显微镜形态的广泛变化无关。我们的发现，即在未能进入乏情期的THX母羊中GnRH的脉冲式分泌增加，支持了这样的假说，即甲状腺对于GnRH神经分泌系统内源性产生的功能转换是必需的，而这种转换会导致母羊繁殖季节的结束。
