Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
J Anim Sci. 2013 Jul;91(7):3041-50. doi: 10.2527/jas.2013-6233. Epub 2013 Jun 4.
The ovarian follicular reserve has been linked to fertility in cattle. Young adult cattle with low vs. high numbers of antral follicles ≥ 3 mm in diameter in follicular waves also have fewer preantral follicles and decreased fertility. This underscores the importance of understanding the factors that regulate early follicular development and establish the ovarian follicular reserve, but little is known about how the follicular reserve is first established. In ruminants and humans, follicles form during fetal life, but there is a gap (about 50 d in cattle) between the appearance of the first primordial follicles and the first growing, primary follicles. In this review we present evidence that in cattle, fetal ovarian steroids (i.e., estradiol and progesterone) are negative regulators of both follicle formation and of the acquisition by newly formed follicles of the capacity to activate (i.e., initiate growth). The results indicate that capacity to activate is linked to the completion of meiotic prophase I by the oocyte. The inhibitory effects of estradiol on follicle activation were found to be reversible and correlated with inhibition of the progression of meiotic prophase I. Fetal bovine ovaries produce steroid hormones and production varies considerably during gestation and in a pattern consistent with the hypothesis that they inhibit follicle formation and capacity of newly formed follicles to activate in vivo. However, little was known about how steroid production is regulated. In our studies, both LH and FSH stimulated progesterone and estradiol production by ovarian pieces in vitro. The addition of testosterone to the culture medium enhanced estradiol production, especially when FSH was also present, but inhibited progesterone production, even in the presence of gonadotropins. Evidence is also presented for effects of maternal nutrition and health and for potential effects of estrogenic endocrine-disrupting chemicals on the size of the ovarian follicular reserve established during fetal life. In summary, fetal ovarian steroids may be important regulators of the early stages of follicular development in cattle. Therefore, external factors that alter steroid production or action may affect the size of the ovarian follicular reserve.
卵巢卵泡储备与牛的生育力有关。在卵泡波中，直径≥3mm 的窦卵泡数量较少的年轻成年牛，其原始卵泡数量也较少，生育力下降。这强调了了解调节早期卵泡发育和建立卵巢卵泡储备的因素的重要性，但对于卵泡储备是如何首先建立的知之甚少。在反刍动物和人类中，卵泡在胎儿期形成，但在第一批原始卵泡出现和第一批生长的初级卵泡出现之间存在一个间隔（牛约 50 天）。在本综述中，我们提出证据表明，在牛中，胎儿卵巢类固醇（即雌二醇和孕酮）是卵泡形成和新形成的卵泡获得激活能力（即启动生长）的负调节剂。结果表明，激活能力与卵母细胞完成减数分裂前期 I 有关。发现雌二醇对卵泡激活的抑制作用是可逆的，并与减数分裂前期 I 的进展抑制相关。胎儿牛卵巢产生类固醇激素，其产生在妊娠期间变化很大，与它们抑制卵泡形成和新形成的卵泡在体内激活能力的假设一致。然而，对于类固醇激素产生如何受到调节知之甚少。在我们的研究中，LH 和 FSH 都刺激卵巢组织体外孕激素和雌二醇的产生。在培养基中添加睾酮可增强雌二醇的产生，尤其是在存在 FSH 时，但抑制孕激素的产生，即使存在性腺激素也是如此。还提出了母体营养和健康的影响以及雌激素类内分泌干扰化学物质对胎儿期建立的卵巢卵泡储备大小的潜在影响的证据。总之，胎儿卵巢类固醇可能是牛卵泡发育早期的重要调节剂。因此，改变类固醇产生或作用的外部因素可能会影响卵巢卵泡储备的大小。
