Estrogen biosynthesis--regulation, action, remote effects, and value of monitoring in ovarian stimulation cycles.
OBJECTIVE
To review current knowledge regarding estrogen biosynthesis, its regulation and action, specifically concerning local as opposed to remote effects of this hormone, and to examine the effectiveness and prognostic value of monitoring hormone concentrations and endometrial response in cycles of controlled ovarian hyperstimulation.


METHODS
Studied that relate specifically to estrogen biosynthesis, enzymatic pathways, estrogen receptor physiology, and the clinical aspects of estrogen monitoring were identified through literature and Medline searches.


RESULTS
Folliculogenesis is the basic unit of ovarian activity, which has a dual purpose: oocyte maturation and steroid production. Steroidogenic granulosa and theca cells cooperate under gonadotropin control to produced estrogens by stimulating synthesis of steroidogenic enzyme messenger RNAs. Steroid synthesis is amplified further by local growth factors and follicular cell multiplication. Estrogen synthesis is directed by FSH, and only small amounts of LH are needed to amplify the follicular estrogenic potential. However, the growth of preovulatory follicles can proceed without LH, under FSH regulation only, even in the presence of low peripheral estrogen levels. Oocyte maturation and fertilization may proceed independently of ambient estrogen levels, leading to the assumption that estrogen exerts a minimal autocrine-paracrine function. The notable effect of follicular estrogen production is to promote adequate receptive endometrium for embryo implantation. Clinical treatment cycles may be monitored more effectively by evaluating end-organ response to estrogen rather than by evaluating absolute serum E2 concentrations or sonographic follicular measurements.


CONCLUSIONS
Follicular estrogen production is regulated by a complex set of signals that synergize to produce optimal steroidogenesis. Most importantly, the effect of estrogen is truly an endocrine effect, as it prepares the endometrium for implantation. Therefore, the goal of effective treatment and monitoring strategies should focus on direct assessment of the biologic activity of estrogen as it optimizes endometrial receptivity in anticipation of subsequent implantation.
Shoham
Z
Z
Department of Obstetrics and Gynecology, Kaplan Hospital, Rehovot, Israel.
Schachter
M
M
D000818:Animals; D004717:Endometrium / Q000254:growth & development; D004967:Estrogens / Q000096:biosynthesis* / Q000266:history / Q000502:physiology; D005260:Female; D049673:History, 20th Century; D006801:Humans; D009865:Oocytes / Q000254:growth & development; D010053:Ovary / Q000502:physiology*; D010060:Ovulation / Q000502:physiology; D011960:Receptors, Estrogen / Q000502:physiology
D004967:Estrogens; D011960:Receptors, Estrogen