Function of the polycystic ovary.
The mechanism of the increase in the number of follicles in polycystic ovaries (PCO) is still not understood, but most data indicate that folliculogenesis is abnormal at all stages. This increase is probably due to prolonged follicle growth in both ovulatory (ov) and anovulatory PCO (anovPCO) rather than over-recruitment from the primordial stage. There appear to be fewer follicles in ovPCO than in anovPCO and this may be due to slow growth combined with arrested development in the anovPCO, preventing the normal process of atresia. This idea is supported by data indicating that the preponderance of structures in anovPCO are functional follicles rather than atretic cysts. In contrast, follicles in ovPCO are primarily atretic, analogous to the situation in the normal ovary. Closer analysis of the function of these follicles reveals an intrinsic defect in the theca cell layer in the expression of the genes encoding steroidogenic enzymes. Although androgen production is increased in all PCOs, the serum concentrations of androgen tended to be higher in anovulatory women indicating that there may be a link between the ovarian concentration and anovulation. Granulosa cells in small follicles from anovPCO behave in a similar fashion to those in preovulatory follicles from normal ovaries in terms of steroidogenic responses. This, in combination with the finding of LH-responsiveness in small follicles from anovPCO, has led to the suggestion that these follicles are prematurely luteinized. The recent finding that follistatin gene regulation may be abnormal in women with polycystic ovary syndrome (PCOS) provides a new insight into the possible defect in the function of these ovaries. Elucidation of the precise nature of the defect may provide the key to understanding the apparent contradiction of increased steroidogenesis in the presence of abnormal and arrested follicle growth.
Mason
Helen
H
Department of Obstetrics and Gynaecology and Department of Physiology, St George's Hospital Medical School, Tooting, London SW17 0RE, UK.