PARENT SESSION
MINISYMPOSIUM VIII. Intragonadal Actions of Estrogen.
11:00 AM-12:30 PM
Harborside D
Chair: Findlay, Jock¹, ¹

(M23) ESTROGEN ACTIONS IN THE OVARY REVISITED.

Findlay, John¹, ¹ Prince Henry's Institute of Medical Research, Clayton, Victoria

ABSTRACT- Estrogens are synonymous with fertility in mammals; however, knowledge of the biological actions of estrogens is incomplete. Two recent developments have thrown new light on the actions of estrogens in mammalian reproduction and will lead to a greater understanding of their functions. They are (a) the identification of a second estrogen receptor, called ER, and (b) mouse models with targeted disruption of the genes encoding both ER and the aromatase enzyme. These models provide for the first time animals which are either unable to respond to endogenous or exogenous estrogens (ER 'knockouts'), or can respond to exogenous estrogen but do not make endogenous estrogen (aromatase 'knockout' or ArKO). Furthermore, the ArKO mouse is a model to study the effects on the ovary of exogenous estrogens of plant and synthetic origin that are of clinical relevance. The data show that estrogens are essential for fertility but not for survival after birth or for the formation of the reproductive tract. This review will focus on the roles of estrogen in folliculogenesis and maintenance of the phenotype of ovarian somatic cells in the mouse. Estrogen is obligatory for normal folliculogenesis beyond the antral stage. We hypothesize that the ER and ER may subserve the proliferative and differentiative actions of estrogen, respectively, within a follicle. Estrogen is required for maintenance of the female phenotype of the somatic cells within the ovaries. This clearly demonstrates a major role for sex steroids in somatic cell differentiation in the gonads of eutherian mammals and challenges the central paradigm that the ovary is the default gonad arising due to the absence of testicular defining signals. Evidence is also provided for the plasticity of the adult female gonad. Reproductive disorders afflicting women today may occur as a result of ovarian dysfunction, and/or ovulatory disorders. Understanding the mechanisms of estrogen actions provides insight into the hormonal regulation of such processes, and into the symptoms associated with menopause. Supported by the NH&MRC of Australia (Regkeys 983212 & 198705)

KEY WORDS: Estrogen, Ovary, Folliculogenesis, Somatic cells