RESPONSE OF MOUSE OVARIES <i>IN VIVO</i> AND IN ORGAN CULTURE TO PREGNANT MARE'S SERUM GONADOTROPHIN AND HUMAN CHORIONIC GONADOTROPHIN

Abstract

Summary. A series of experiments was carried out to assess the effects of HCG in vivo and in organ culture, on mouse oocyte and follicle maturation following PMSG treatment in vivo. Preovulatory maturation and its relationship to time of injection and duration of hormone treatment was assessed using quantitative histological techniques. The general pattern and timing of meiotic changes was similar in organ culture to that occurring in the intact animal, although fewer oocytes reached metaphase II and ovulation was a rare event. This deficiency in the cultured ovaries was related to the destruction of Graafian follicles during the preparation of explants. The stage of meiosis reached by the oocyte was largely a factor of critical time intervals, but the size of the follicle also had an important limiting effect. Thus, medium-sized and small antral follicles contained oocytes whose meiotic maturation was seemingly `blocked' at metaphase I, while Graafian follicles either reached metaphase II or persisted at the dictyate stage. These results are discussed in the light of current knowledge of oocyte/follicle cell interactions and the mode of action of gonadotrophic hormones.