Ovarian follicular growth in humans: ovarian ageing and population of growing follicles

Abstract

By integrating morphometrical and endocrinological data, as well as biological effects of various peptides synthesized by the primate follicle, the current review proposes a morphofunctional view of the early follicle growth within the human ovary. From the time they enter the preantral stage (0.15 mm), during the early luteal phase, follicles need about 70 days to reach a size of 2 mm. These follicles are impervious to cyclic FSH and LH changes in terms of granulosa cell (GC) proliferation, and their steroidogenic activity is very low. From the time they enter the selectable stage (2-5 mm in diameter) during the late luteal phase, follicles become sensitive to cyclic changes of FSH in terms of quality and GC proliferation, but not in terms of GC aromatase activity. Thus, as the follicle develops, its responsiveness to gonadotropins progressively increases. In vitro studies suggest that this progressive acquisition of follicular cell responsiveness to gonadotropins might be under the control of peptides acting in an autocrine/paracrine fashion within the follicle. The numbers of growing follicles decrease with ageing, especially in women over the age of 40. During the follicular phase of the menstrual cycle, selectable follicles exhibit a mitotic activity of their GC higher in women older than 40 years than in younger women.