Estrogen and folliculogenesis: is one necessary for the other?
OBJECTIVE
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.


RESULTS
Estrogen appears to regulate cyclic gonadotropin release via its action on estrogen receptor alpha in the hypothalamus/hypophysis axis and to enhance folliculogenesis through its actions via estrogen receptor beta 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.


CONCLUSIONS
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.
Kolibianakis
Efstratios M
EM
Centre for Reproductive Medicine, Dutch-Speaking Brussels Free University, Brussels, Belgium. Stratis.Kolibianakis@otenet.gr
Papanikolaou
Evangelos G
EG
Fatemi
Human M
HM
Devroey
Paul
P
D000818:Animals; D001141:Aromatase / Q000235:genetics; D004967:Estrogens / Q000502:physiology*; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology; D051379:Mice; D023421:Models, Animal; D006080:Ovarian Follicle / Q000502:physiology*; D011960:Receptors, Estrogen / Q000235:genetics
D004967:Estrogens; D011960:Receptors, Estrogen; D001141:Aromatase