Luteolysis

Luteolysis (also known as luteal regression) is the structural and functional degradation of the corpus luteum (CL), which occurs at the end of the luteal phase of both the estrous and menstrual cycles in the absence of pregnancy. In domestic animals, luteolysis is initiated by the hormones prostaglandin F2alpha and oxytocin. In sheep, communication between the pars nervosa (posterior lobe of the pituitary gland), corpus luteum, and the uterus endometrium via the circulatory system is required for luteolysis. Studies with sheep have found that, if the uterine horn is ipsalateral to the ovary possessing the CL is surgically removed, the lifespan of the corpus luteum will increase drastically.

Luteolysis in primates (including humans), however, is not caused by prostaglandin, and removal of the uterus will not prolong the life of the corpus luteum. However, primates do respond to PGF2a, and asthmatics should take great care when handling this hormone as PGF2a is bronchoconstrictor.

Estrogen, secreted by Granulosa Cells and primarily progesterone, secreted by the corpus luteum, inhibit the release of luteinizing hormone (LH) and Follicle Stimulating Hormone (FSH) by the adenohypophysis (anterior lobe of the pituitary gland) via classical negative feedback mechanisms. This removes the luteotrophic support provided by the gonadotropin luteinizing hormone (LH). During a pregnancy, the corpus luteum remains on the ovary releasing progesterone which will maintain a state of uterine quiescence and close the cervix until the delivery of the fetus. Alternatively if no implantation of a blastocyst occurs, the corpus luteum is degraded to a corpus albicans (scar tissue) by PGF2alpha released by uterine endometrial cells.

Degradation of the corpus luteum will result in reduced levels of progesterone, promoting an increase in follicle-stimulating hormone (FSH) secretion by the adenohypophysis, which will trigger the development of a new follicle on the ovary.

If pregnancy occurs, the placental hormone chorionic gonadotropin continues to maintain the corpus luteum, but in some species it will eventually degrade sometime during pregnancy.

If pregnancy occurs in equine, the placental hormone equine chorionic gonadotropin released by endometrial cup continue to maintain the progesterone by acting as LH and FSH for follicles in ovary which will in return lead to increase in amount of corpus luteum.

Luteolytic agents

• Danazol was described as a luteolytic agent.^[1]
• Cloprostenol is another example of such an agent.

References

1. Wentz AC, Sapp KC. Danazol as a luteolytic agent. Fertil Steril. 1978;29(1):23-5. PMID 620838

• Bagnell, C. 2005. "Animal Reproduction". Rutgers University Department of Animal Sciences.
• Hadley, M.E. and Levine, J.E. 2007. Endocrinology, 6th Edition.
• Philip L. Sanger