Department of Endocrinology, The Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences, Instytucka 3, Jabłonna, Poland.
Anim Reprod Sci. 2010 Aug;121(1-2):84-93. doi: 10.1016/j.anireprosci.2010.05.006. Epub 2010 May 20.
There is juvenile hiatus during maturation of larger mammals with relatively long life spans. Using histomorphological and functional criteria we describe the feedback mechanisms which could play a role in the regulation of the gonadotrophic axis during the postnatal transition to the quiescent prepubertal period in sheep. The aim of this study was to determine the influence of ovarian factors on the endocrine activity of gonadotroph cells, the site of synthesis, storage and release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), in adenohypophyses of weanling and weaned prepubertal lambs. The examination was made in (i) 9-week-old infantiles, suckling lambs undergoing weaning, ovary-intact (OVI) and ovariectomised (OVX) at the 6th week of age, and (ii) 16-week-old juveniles OVI and OVX at the 12th week of age (n=5 per group). Changes in gonadotrophs were assayed with hybridohistochemistry, immunohistochemistry and radioimmunoassay. The percentage of the adenohypophyseal area (PA) occupied by gonadotrophs containing LHbeta-mRNA and immunoreactive for LHbeta was lower (P<0.05), whereas the PA occupied by cells containing FSHbeta-mRNA and immunoreactive for FSHbeta was higher (P<0.05) in the 16-week-old OVI lambs in comparison with the 9-week-old ones. The mean concentration and basal level of LH in the peripheral blood plasma were greater (P<0.05) in the 16-week-old OVI lambs in comparison with the 9-week-old group, whereas the circulating FSH was not different. In the OVX 9-week-old lambs, the PA occupied by gonadotrophs containing LHbeta-mRNA and the plasma LH concentration, basal level, pulse frequency and amplitude were greater (P<0.05), whereas the PA occupied by cells immunoreactive for LHbeta was lower (P<0.05) in comparison with the OVI group. In the OVX 16-week-old lambs, the PA occupied by gonadotrophs containing LHbeta-mRNA and immunoreactive for LHbeta, the LH plasma concentration, basal level and pulse frequency were (P<0.05) greater in comparison with the OVI group. The PA occupied by gonadotrophs containing FSHbeta-mRNA and the plasma FSH concentration were greater (P<0.05) in the OVX 9- and 16-week-old lambs in comparison with the OVI ones. The ovariectomy had no effect on the PA occupied by cells immunoreactive for FSHbeta in both age stages. In conclusion, ovarian factors may play inhibitory role in regulating both LH and FSH synthesis rate and release and stimulatory role in regulating LH storage in adenohypophyseal gonadotrophs in infantile lambs. In lambs at the beginning of the juvenile period, ovarian factors may play only inhibitory role in regulating both LH and FSH synthesis and release and LH storage. The effects of ovarian hormones on the gonadotrophin storage, i.e. releasable pools in adenohypophyseal cells, are specific for LH, no such effects are apparent on FSH in lambs during the postnatal transition to prepuberty. Thus, the initiation of the juvenile period in female sheep is a function of change of the stimulatory role of ovarian hormones in regulating LH storage to the inhibitory one.
在较大的、寿命较长的哺乳动物成熟过程中存在幼年休止期。本研究利用组织形态学和功能学标准，描述了在绵羊出生后向静止的初情期过渡过程中，可能在调节性腺轴功能中起作用的反馈机制。本研究的目的是确定卵巢因子对促性腺细胞内分泌活性的影响，即促黄体生成素（LH）和促卵泡激素（FSH）的合成、储存和释放的位点，研究对象为断奶和未断奶的青春期前羔羊的腺垂体。（i）9 周龄的婴儿，正在断奶的羔羊，6 周龄时进行卵巢完整（OVI）和卵巢切除术（OVX），（ii）16 周龄的青少年，OVI 和 OVX 分别在 12 周龄（每组 5 只）。通过杂交组织化学、免疫组织化学和放射免疫测定检测促性腺激素的变化。与 9 周龄的 OVI 羔羊相比，16 周龄的 OVI 羔羊的促性腺细胞中含有 LHβ-mRNA 和 LHβ免疫反应性的腺垂体面积（PA）所占比例较低（P<0.05），而含有 FSHβ-mRNA 和 FSHβ免疫反应性的细胞的 PA 所占比例较高（P<0.05）。与 9 周龄的羔羊相比，16 周龄的 OVI 羔羊的外周血血浆 LH 平均浓度和基础水平更高（P<0.05），而循环 FSH 则没有差异。在 9 周龄的 OVX 羔羊中，含有 LHβ-mRNA 的促性腺细胞的 PA 和血浆 LH 浓度、基础水平、脉冲频率和幅度更高（P<0.05），而含有 LHβ免疫反应性的细胞的 PA 则更低（P<0.05）。在 16 周龄的 OVX 羔羊中，含有 LHβ-mRNA 和 LHβ免疫反应性的促性腺细胞的 PA、LH 血浆浓度、基础水平和脉冲频率更高（P<0.05）。与 OVI 组相比，OVX 9 周龄和 16 周龄羔羊的含有 FSHβ-mRNA 的促性腺细胞的 PA 和血浆 FSH 浓度更高（P<0.05）。OVX 对两个年龄段的 FSHβ免疫反应性细胞的 PA 没有影响。总之，卵巢因子可能在调节 LH 和 FSH 合成率和释放以及调节 LH 在腺垂体促性腺细胞中的储存方面发挥抑制作用。在幼年期开始时，卵巢因子可能仅在调节 LH 和 FSH 的合成和释放以及 LH 储存方面发挥抑制作用。卵巢激素对促性腺激素储存的影响，即腺垂体细胞中可释放的池，对 LH 是特异性的，在绵羊向青春期过渡期间，对 FSH 没有这种作用。因此，雌性绵羊青春期的开始是卵巢激素在调节 LH 储存方面从刺激作用转变为抑制作用的功能。
