Baird D T, McNeilly A S
J Reprod Fertil Suppl. 1981;30:119-33.
In the adult non-pregnant ewe the secretion of FSH is sufficient to ensure a continuous growth and development of antral follicles to 3-5 mm size at all times. Further development and increased secretion of oestradiol through the final 72 h to ovulation depends on adequate stimulation by LH. During anoestrus and the luteal phase of the cycle LH pulses occur too infrequently to stimulate sufficient oestradiol to evoke an LH surge. Moreover, during the luteal phase progesterone secreted by the corpus luteum not only reduces the frequency of LH pulses but also inhibits the ability of oestrogen to evoke an LH surge. At the time of luteal regression the frequency of LH pulses increases to at least one per hour due to the fall in progesterone secretion. This change in pulse frequency of LH is associated with a decrease in the secretion of FSH, probably because of a direct inhibitory action of oestrogen on the anterior pituitary gland. The dominant follicle is probably relatively independent of circulating levels of FSH due to the high concentration of oestradiol and FSH within the microenvironment of the follicular cavity. Once the oestrogen secretion achieves a certain level a preovulatory surge of LH (and FSH) occurs. Increased sensitivity of the anterior pituitary to LH-RH and increased secretion of LH-RH from the hypothalamus both play a part in producing the LH surge. The rise in prolactin at this time probably reflects a decrease in hypothalamic dopamine turnover which is necessary for maximum release of LH-RH. The preovulatory LH surge initially stimulates and then totally inhibits further secretion of oestrogen and androgen from the ovulatory follicle. This suppression of steroid secretion is accompanied by a second peak of FSH at about the time of ovulation. The function of this second peak of FSH remains unknown although it may be responsible for the development of the large antral follicles which occur on Days 3 and 4. It is probably more important in those mammals like the rat and hamster which only form a functional corpus luteum if pregnancy occurs and in which oestrogen is necessary for implantation.
在成年未孕母羊中，促卵泡素（FSH）的分泌足以确保窦状卵泡始终持续生长并发育至3 - 5毫米大小。在排卵前的最后72小时内，卵泡进一步发育以及雌二醇分泌增加取决于促黄体生成素（LH）的充分刺激。在发情间期和发情周期的黄体期，LH脉冲出现的频率过低，无法刺激产生足够的雌二醇以引发LH峰。此外，在黄体期，黄体分泌的孕酮不仅会降低LH脉冲的频率，还会抑制雌激素引发LH峰的能力。在黄体退化时，由于孕酮分泌减少，LH脉冲频率增加至至少每小时一次。LH脉冲频率的这种变化与FSH分泌减少有关，这可能是由于雌激素对垂体前叶的直接抑制作用。优势卵泡可能相对独立于循环中的FSH水平，因为卵泡腔内微环境中雌二醇和FSH浓度较高。一旦雌激素分泌达到一定水平，就会出现LH（和FSH）的排卵前峰。垂体前叶对促性腺激素释放激素（LH - RH）敏感性增加以及下丘脑LH - RH分泌增加，在产生LH峰过程中均起作用。此时催乳素升高可能反映了下丘脑多巴胺周转率降低，这是LH - RH最大程度释放所必需的。排卵前LH峰最初刺激然后完全抑制排卵卵泡中雌激素和雄激素的进一步分泌。这种类固醇分泌的抑制伴随着排卵时FSH的第二个峰值。尽管FSH的第二个峰值可能负责第3天和第4天出现的大型窦状卵泡的发育，但其功能仍不清楚。在大鼠和仓鼠等哺乳动物中，它可能更为重要，因为这些动物只有在怀孕时才形成功能性黄体，并且雌激素对于着床是必需的。
