Modifications in gonadotropin signaling: a key to understanding cyclic ovarian function.

The enigma in understanding the regulation of ovarian function throughout the menstrual cycle is that both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) act on the ovary, at least in part through the cyclic adenosine monophosphate (cAMP) intracellular signaling pathway. If cAMP is a common intracellular messenger of gonadotropic stimulation during both the follicular and the luteal phases, how can the responses of the follicle and the corpus luteum to their respective trophic hormones differ so dramatically? The actions of FSH and LH on the ovary are summarized and a mechanistic hypothesis is provided as to how ovarian cyclicity (initiation of follicular development, selection of a single preovulatory follicle, corpus luteum function, corpus luteum regression, and corpus luteum rescue during early pregnancy) could be controlled by a single intracellular messenger: cAMP.