Figure 2.

Pathophysiology of the PCOS reproductive phenotype. There is increased frequency of pulsatile GnRH release that selectively increases LH secretion. LH stimulates ovarian theca cell T production. T is incompletely aromatized by the adjacent granulosa cells because of relative FSH deficiency. There are also constitutive increases in the activity of multiple steroidogenic enzymes in polycystic ovaries contributing to increased androgen production. Increased adrenal androgen production may also be present in PCOS. T acts in the periphery to produce signs of androgen excess, such as hirsutism, acne, and alopecia. T and androstenedione can also be aromatized extragonadally to estradiol and estrone, respectively, resulting in unopposed estrogen action on the endometrium. T feeds back on the hypothalamus to decrease the sensitivity to the normal feedback effects of estradiol and progesterone to slow GnRH pulse frequency. This figure is used with the permission of Andrea Dunaif.