How does progesterone play a role in a feedback mechanism?
The secretion of gonadotrophins from the pituitary in women is under ovarian control via negative and positive feedback mechanisms. Steroidal and non-steroidal substances mediate the ovarian effects on the hypothalamic-pituitary system. During the follicular phase of the cycle, estradiol (E2) plays a key role, while circulating progesterone (at low concentrations) and inhibin B contribute to the control of LH and FSH secretion respectively. During the luteal phase, both E2 and progesterone regulate secretion of the two gonadotrophins, while inhibin A plays a role in FSH secretion. The intercycle rise of FSH is related to changes in the levels of the steroidal and non-steroidal substances during the luteal-follicular transition. In terms of the positive feedback mechanism, E2 is the main component sensitizing the pituitary to GnRH. Activity of a non-steroidal ovarian substance, named gonadotrophin surge-attenuating factor (GnSAF), has been detected after ovarian stimulation. It is hypot
