HAMMOND MEMORIAL LECTURE

Abstract

As far as meiotic resumption is concerned, oocyte competence is acquired long before the preovulatory gonadotrophin surge, before antrum formation, immediately afterwards or later on. Competent oocytes resuming meiosis when isolated from the follicle are able to cleave after parthenogenetic activation. Protein synthesis does not change during oocyte meiotic resumption in vitro in the same way as it does intrafollicularly. When considering the ability of the oocyte to associate with the male gamete, to recognize its enzymes or to support its participation, it must be remembered that the oocyte remains dependent on the follicle almost up to the moment of follicle rupture. This role of the follicle is probably achieved in vivo by a classical sequential steroid action, when the LH [luteinizing hormone] surge dramatically changes the intrafollicular steroid content. In the ovary, cyclic changes in estradiol and FSH [follicle stimulating hormone] levels stimulate 1 or 2 waves of follicular growth. In vivo FSH and estradiol play a major role in the regulation of ovulation rates, during the transition from the preantral to the antral stage and some days before ovulation, when atresia reduces the number of preovulatory follicles. The ovulation of increased numbers of completely matured oocytes, or the preparation of a large population of LH-sensitive follicles for maturation in vitro, needs a better understanding of follicular cycles. An approach is suggested in rodents, ruminants and primates.