Gonadotropin Signaling in the Ovary

This chapter discusses signaling pathways through which follicle-stimulating hormone (FSH) promotes follicle maturation and luteinizing hormone (LH) promotes ovulation and corpus luteum formation. The gonadotropic hormones FSH and LH initiate signaling events in ovarian target cells that govern the reproductive cycle and thus the continuation of a species. The ovarian follicle is the key structure that houses the oocyte, and upon appropriate stimulation by FSH and LH, follicles produce hormones that promote the development of secondary sex characteristics and that regulate the hypothalamic–pituitary axis as well as uterine receptivity. Additionally, the follicle must extrude the oocyte at an appropriate time to allow for fertilization, and remaining cells within the follicle must differentiate into cells of the corpus luteum that produce hormones necessary to sustain pregnancy. Although there is a great deal of species variability, LH is uniformly required to initiate progesterone production by the corpus luteum, which is necessary for implantation and the maintenance of pregnancy. In the absence of FSH, follicles do not develop beyond the preantral stage, and animals are infertile. Similarly, in the absence of LH, ovulation does not ensue, corpora lutea do not form, and animals are infertile. Both gonadotropic hormones initiate their activities by binding to surface protein receptors.