Contemporary insights into the control of the corpus luteum function

Increasing evidence has been accumulated to confirm the critical dependency of the corpus luteum function from regular pituitary luteinizing hormone (LH) inputs. In fact, close temporal and functional links have been demonstrated between intermittent LH stimulations and episodic sex steroid release emanating from the mature corpus luteum. Moreover, an intrinsically pulsatile progesterone (P4) release independent of, but facilitated by gonadotropin inputs has been observed from the corpus luteum in vitro. This may suggest some functional autonomy in this organ, at least within close temporal limits. The pulsatile P4 secretion may be optimally maintained by gonadotropin stimulations effected at frequencies and amplitudes similar to those observed during the luteal phase in vivo. Since autonomous P4 secretion is modulated, amongst other determinants, by prostaglandins, oxytocin and P4 itself, ultra-short feedback loops are assumed to exist for an optimal tuning of the luteal function. This episodic sex steroid release from the corpus luteum may be required to set the endocrine signal for the blastocyst to implant.