Driancourt M A, Webb R, Fry R C
INRA, Reproductive Physiology, Nouzilly, France.
J Reprod Fertil. 1991 Sep;93(1):63-70. doi: 10.1530/jrf.0.0930063.
The process by which a single follicle is selected to ovulate while others regress is unknown in ewes. If the dominant follicle secretes substances that directly inhibit the growth of other follicles, the superovulatory response to the administration of exogenous gonadotrophins may be blunted. Administration of 1250 iu pregnant mares' serum gonadotrophin (PMSG) before or after the emergence of the dominant follicle in the follicular phase, or 1000 iu PMSG in the presence or absence of a large healthy or atretic follicle during the luteal phase did not affect the induced ovulatory response. Comparisons between the ovary with or without the dominant follicle did not reveal any differences in ovulatory response to PMSG. The in-vitro features (i.e. mitotic index, oestradiol and testosterone production) of follicles ipsilateral or contralateral to the dominant follicle during the early and late follicular phases were also similar. If the dominant follicle secretes substances detrimental to the other follicles, this could be mimicked in vitro. Co-culture of small follicles with the largest follicles in a closed system did not reduce their incorporation of 3H thymidine in granulosa cells, compared with small follicles cultured alone. These data suggest that dominance is probably not operative in sheep. The administration of 500 iu of PMSG during the midfollicular phase increased ovulation rate in Merino ewes, indicating that dominance is essentially passive in ewes and can easily be overcome by raising gonadotrophin concentration.
在母羊中，单个卵泡被选择排卵而其他卵泡退化的过程尚不清楚。如果优势卵泡分泌直接抑制其他卵泡生长的物质，那么对外源性促性腺激素给药的超排卵反应可能会减弱。在卵泡期优势卵泡出现之前或之后给予1250国际单位孕马血清促性腺激素（PMSG），或者在黄体期存在或不存在大的健康或闭锁卵泡的情况下给予1000国际单位PMSG，均不影响诱导的排卵反应。有或没有优势卵泡的卵巢之间的比较未发现对PMSG的排卵反应有任何差异。卵泡期早期和晚期优势卵泡同侧或对侧卵泡的体外特征（即有丝分裂指数、雌二醇和睾酮生成）也相似。如果优势卵泡分泌对其他卵泡有害的物质，这在体外可以模拟。与单独培养的小卵泡相比，在封闭系统中将小卵泡与最大卵泡共培养不会降低其颗粒细胞中3H胸苷的掺入。这些数据表明，优势现象在绵羊中可能不起作用。在卵泡中期给予500国际单位PMSG可提高美利奴母羊的排卵率，这表明在母羊中优势现象基本上是被动的，并且可以通过提高促性腺激素浓度轻易克服。
