Aromatase inhibitor treatment

Clomiphene citrate: (Day 5) Administration of CC from days 3 to 7 results in ER depletion at the level of the pituitary and mediobasal hypothalamus. As a result, estrogen negative feedback centrally is interrupted and FSH secretion increases from the anterior pituitary leading to multiple follicular growth. (Day 10) By the late follicular phase, because of the long tissue retention of CC, there continues to be ER depletion centrally and increased E2 secretion from the ovary is not capable of normal negative feedback on FSH. The result is multiple dominant follicle growth and multiple ovulation.
Aromatase inhibitor: (Day 5) Administration of an AI from 3 to 7 days results in suppression of ovarian E2 secretion and reduction in estrogen negative feedback at the pituitary and mediobasal hypothalamus. Increased FSH secretion from the anterior pituitary results in stimulation of multiple ovarian growth. (Day 10) Later in the follicular phase, the effect of the AI is reduced and E2 levels increase as a result of follicular growth. Because AIs do not affect ERs centrally, the increased E2 levels result in normal negative feedback on FSH secretion and follicles less than dominant follicle size undergo atresia, with resultant monofollicular ovulation in most cases.