Germinal vesicle breakdown in oocytes of human atretic follicles during the menstrual cycle

Histological examination was performed on 975 antral follicles (1-12 mm) from 17 large ovarian resections and 79 whole ovaries collected from 63 women with normal ovarian function at different stages during the menstrual cycle. The meiotic stage of the oocyte was examined in relation to the degree of atresia and size of follicles throughout the menstrual cycle. In healthy follicles the oocytes were in the dictyate stage. In atretic follicles 10% of the oocytes exhibited germinal vesicle breakdown (GVBD) and 20% were necrotic. The percentage of GVBD oocytes in atretic follicles was closely related to the degree of follicular atresia and to the follicle diameter. GVBD percentage rose sharply in the periovulatory period although there was no change of mean follicle size or quality during this period. Such a cyclic evolution in GVBD percentages indicates that the removal of inhibition (due to atresia) exerted by the follicle itself on the germinal vesicle is insufficient to induce the resumption of meiosis in the human oocyte; specific induction seems to be necessary, at least to produce complete nuclear maturation.