Estrogen and folliculogenesis: is one necessary for the other?

Purpose of review During folliculogenesis the primordial follicle undergoes several steps of maturation in order to develop into a preovulatory follicle. The exact role of estrogen during this process has not yet been fully assessed. Recent findings Estrogen appears to regulate cyclic gonadotropin release via its action on estrogen receptor a in the hypothalamus/ hypophysis axis and to enhance folliculogenesis through its actions via estrogen receptor in the ovary. In addition, a role of estrogen during the very early stages of folliculogenesis is possible. However, it is likely that oocyte quality and developmental potential are not estrogen dependent. This might explain the lack of association between estrogen and in-vitro fertilization outcome in humans. Summary The advent of knockout mice models has enhanced our understanding of the role of estrogen during folliculogenesis. Existing data suggest that estrogen might be involved in the very early steps of this process, but its role in sustaining ovulation is mainly central.