Progesterone is a steroid hormone that plays a role in maintaining the female menstrual cycle, pregnancy and human development. Progesterone is produced in the ovaries, adrenal glands and placenta. During the menstrual cycle, estrogen stimulates growth of the endometrium, which is the inner lining of the uterus. After ovulation, progesterone secreted by the ovaries inhibits further growth of the endometrium and stimulates tissue remodeling. Endometriosis is a condition in which the endometrium grows in places outside of the uterus, most often on the ovaries. A review in the November 2005 issue of “Human Reproduction Update” notes that progestins, which are synthetic progesterone mimics, have been used for over 40 years to treat endometriosis.
Inhibits Cell Growth
Progesterone directly inhibits the growth of endometrial cells. A review in the journal “Human Reproduction” purports that progestins stimulate atrophy or regression of endometrial lesions. Another review in “Human Reproduction Update” notes that a study that evaluated the efficacy of progestin treatment for endometriosis in several studies found progestins reduced or eliminated pain symptoms in approximately 90 percent of women. The effectiveness of progestins for treating endometriosis is not just linked to its growth inhibiting actions, but also to its induction of anovulation, inhibition of blood vessel growth and anti-inflammatory actions.
Reduces Hormone Levels
Continuous administration of progesterone inhibits ovulation and lowers estrogen levels. It also lowers the secretion of other hormones that are critical for maintaining the menstrual cycle. In some women, pain associated with endometriosis is more pronounced during menstruation and progestin treatment attenuates this pain by preventing menstruation.
Inhibits Vessel Growth
During each menstrual cycle, estrogen stimulates growth of the endometrium which is also accompanied by increased blood vessel growth to supply the tissue with oxygen and nutrients. Blood vessel growth also occurs in endometrial cysts, causing them to enlarge and become more painful. A study in a mouse model of endometriosis in the July 2009 issue of “MHR Basic Science of Reproductive Medicine" reports that progesterone inhibits blood vessel growth in endometrial tissue.
The outgrowth of endometrial cysts elicits an inflammatory response, which contributes to the painfulness of the condition. The review in “Human Reproduction Update” reports that studies have also demonstrated that progestins reduce inflammation in women with endometriosis.