Endocrine regulation of the corpus luteum.

Abstract

The corpus luteum is a small gland that develops rapidly from the ovulated follicle and performs a vital function in the reproductive process, namely, the secretion of progesterone, which is necessary for implantation of the blasto­ cyst. Following implantation, the continued secretion of progesterone is essential to maintain a quiescent uterus and an intrauterine environment that is conducive to continued development of the embryo (29). If fertilization or implantation does not occur, the corpus luteum regresses, and the consequent withdrawal of progesterone leads to increased frequency of pulsatile luteiniz­ ing hormone (LH) secretion, increased follicular estrogen synthesis, and a new follicular phase (56). If implantation occurs, then the embryo signals the corpus luteum either directly or indirectly to continue to secrete progesterone and to prevent the corpus luteum from regressing (78). Thus, the corpus luteum can be viewed as the terminal stage of the ovarian follicle, which after shedding the oocyte, continues to nurture the (fertilized) egg indirectly by producing progesterone. The progestational changes in the uterus must pre­ cede the arrival of the preimplantation embryo and require the rapid conver­ sion of the predominantly estrogen-producing follicle to a predominantly progesterone-producing corpus luteum. This is accomplished by the pre­ ovulatory surge of luteinizing hormone, which serves the dual role of stimulating both ovulation and the conversion of the follicle into a corpus luteum, a process known as luteinization (57). This review COncentrates On certain aspects of the regulation of the corpus luteum that represent relatively new directions in research, and emerging concepts. For more information about the regulation of the corpus luteum in