Progestogens (also sometimes spelled progestagens or gestagens) are a class of steroid hormones that bind to and activate the progesterone receptor (PR). The most important progestogen in the body is progesterone (P4). Other endogenous progestogens include 17-hydroxyprogesterone, 5α-dihydroprogesterone, and 11-deoxycorticosterone. Synthetic progestogens are generally referred to as progestins. However, the terms progesterone, progestogen, and progestin are frequently used interchangeably both in the scientific literature and in clinical settings.
The progestogens are one of the five major classes of steroid hormones, in addition to the androgens, estrogens, glucocorticoids, and mineralocorticoids, as well as the neurosteroids. All progestogens are characterized by their basic 21-carbon skeleton, called a pregnane skeleton (C21). In similar manner, the estrogens possess an estrane skeleton (C18), and androgens, an andrane skeleton (C19).
In the first step in the steroidogenic pathway, cholesterol is converted into pregnenolone (P5), which serves as the precursor to the progestogens progesterone and 17-hydroxyprogesterone. These progestogens, along with another steroid, 17-hydroxypregnenolone, are the precursors of all other endogenous steroids, including the androgens, estrogens, glucocorticoids, mineralocorticoids, and neurosteroids. Thus, many tissues producing steroids, including the adrenal glands, testes, and ovaries, produce progestogens.
In some tissues, the enzymes required for the final product are not all located in a single cell. For example, in ovarian follicles, cholesterol is converted to androstenedione, an androgen, in the theca cells, which is then further converted into estrogen in the granulosa cells. Fetal adrenal glands also produce pregnenolone in some species, which is converted into progesterone and estrogens by the placenta (see below). In the human, the fetal adrenals produce dehydroepiandrosterone (DHEA) via the pregnenolone pathway.
Production by the ovary
Progesterone is the major progestogen produced by the corpus luteum of the ovary in all mammalian species. Luteal cells possess the necessary enzymes to convert cholesterol to pregnenolone, which is subsequently converted into progesterone. Progesterone is highest in the diestrus phase of the estrous cycle.
Production by the placenta
The role of the placenta in progestogen production varies by species. In the sheep, horse, and human, the placenta takes over the majority of progestogen production, whereas in other species the corpus luteum remains the primary source of progestogens. In the sheep and human, progesterone is the major placental progestogen.
The equine placenta produces a variety of progestogens, primarily 5α-dihydroprogesterone and 5α,20α-tetrahydroprogesterone, beginning on day 60. A complete luteo-placental shift occurs by day 120–150.
In women, progestogens are commonly used to prevent endometrial hyperplasia from unopposed estrogen during hormone replacement therapy. They also used to treat secondary amenorrhea, dysfunctional uterine bleeding and endometriosis.
In a normal menstrual cycle, declining levels of progesterone triggers menstruation. Norethindrone acetate and medroxyprogesterone acetate may be used to artificially induce progestogen-associated breakthrough bleeding.
In addition to their progestogen properties, some progestins are antagonists of the androgen receptor, and can be used clinically as antiandrogens. Examples include chlormadinone acetate, cyproterone acetate, dienogest, and drospirenone. Care must be taken as to which progestin is used however, as various others, such as levonorgestrel and norethindrone acetate, conversely have androgenic properties.
Progestogens, similarly to the androgens and estrogens through their own respective receptors, inhibit the secretion of the gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) via activation of the progesterone receptor. This effect is form of negative feedback on the hypothalamic-pituitary-gonadal (HPG) axis that the body uses to prevent sex hormone levels from becoming too elevated. Accordingly, progestogens, both endogenous and exogenous (i.e., progestins), have antigonadotropic effects, and progestins in sufficient amounts can markedly suppress the body's normal production of progestogens, androgens, and estrogens, as well as, in theory, neurosteroids. As such, some of the more potent progestins, including chlormadinone acetate, medroxyprogesterone acetate, megestrol acetate, nomegestrol acetate, and norethisterone acetate are sometimes used to suppress sex hormone levels in a variety of androgen and estrogen-associated conditions. Examples of indications include treating sex hormone-sensitive cancers (e.g., breast cancer), suppressing precocious puberty and puberty in transgender youth, and reducing sex drive in sex offenders.
Progesterone itself is not employed as an antigonadotropin, as it can function as a prohormone to androgens and estrogens, especially at the relatively high doses that would be necessary to achieve sufficient antigonadotropic action.
In many people suffering from solid malignancy, especially gastric and pancreatic cancer, high doses of certain progestins can be employed to improve appetite and reduce wasting. In general, they are used in combination with certain other steroids such as dexamethasone. Their effects take several weeks to become apparent, but are relatively long-lived when compared to those of corticosteroids. Furthermore, they are recognized as being the only drugs to increase lean body mass. Megestrol acetate is the lead drug of this class for the management of cachexia, and medroxyprogesterone acetate is also used.
- Tekoa L. King; Mary C. Brucker (25 October 2010). Pharmacology for Women's Health. Jones & Bartlett Publishers. p. 373. ISBN 978-1-4496-5800-7.
- Michelle A. Clark; Richard A. Harvey; Richard Finkel; Jose A. Rey, Karen Whalen (15 December 2011). Pharmacology. Lippincott Williams & Wilkins. p. 322. ISBN 978-1-4511-1314-3.
- Bhattacharya (1 January 2003). Pharmacology, 2/e. Elsevier India. p. 378. ISBN 978-81-8147-009-6.
- Tara Parker-Pope (25 March 2008). The Hormone Decision. Simon and Schuster. p. 228. ISBN 978-1-4165-6201-6.
- Hickey M, Fraser IS (August 2000). "A functional model for progestogen-induced breakthrough bleeding". Hum. Reprod. 15 Suppl 3: 1–6. PMID 11041215.
- Raudrant D, Rabe T (2003). "Progestogens with antiandrogenic properties". Drugs 63 (5): 463–92. doi:10.2165/00003495-200363050-00003. PMID 12600226.
- de Lignières B, Silberstein S (April 2000). "Pharmacodynamics of oestrogens and progestogens". Cephalalgia : an International Journal of Headache 20 (3): 200–7. doi:10.1046/j.1468-2982.2000.00042.x. PMID 10997774.
- Chassard D, Schatz B (2005). "[The antigonadrotropic activity of chlormadinone acetate in reproductive women]". Gynécologie, Obstétrique & Fertilité (in French) 33 (1-2): 29–34. doi:10.1016/j.gyobfe.2004.12.002. PMID 15752663.
- Brady BM, Anderson RA, Kinniburgh D, Baird DT (April 2003). "Demonstration of progesterone receptor-mediated gonadotrophin suppression in the human male". Clinical Endocrinology 58 (4): 506–12. doi:10.1046/j.1365-2265.2003.01751.x. PMID 12641635.
- Neumann F (1978). "The physiological action of progesterone and the pharmacological effects of progestogens--a short review". Postgraduate Medical Journal. 54 Suppl 2: 11–24. PMID 368741.
- Andrea R. Genazzani (15 January 1993). Frontiers in Gynecologic and Obstetric Investigation. Taylor & Francis. p. 320. ISBN 978-1-85070-486-7. Retrieved 29 May 2012.
- Lello S (March 2010). "Nomegestrol acetate: pharmacology, safety profile and therapeutic efficacy". Drugs 70 (5): 541–59. doi:10.2165/11532130-000000000-00000. PMID 20329803.
- Garza-Flores J, Menjívar M, Cardenas M, Reynoso M, García GA, Pérez Palacios G (January 1991). "Further studies on the antigonadotropic mechanism of action of norethisterone". The Journal of Steroid Biochemistry and Molecular Biology 38 (1): 89–93. doi:10.1016/0960-0760(91)90406-U. PMID 1825472.
- Christiane Northrup (1 June 2010). Women's Bodies, Women's Wisdom: Creating Physical and Emotional Health and Healing. Hay House, Inc. p. 552. ISBN 978-0-553-38673-8. Retrieved 29 May 2012.
- Ifeoma Ikenze (24 November 1998). Menopause & Homeopathy: A Guide for Women in Midlife. North Atlantic Books. p. 18. ISBN 978-1-55643-291-0. Retrieved 29 May 2012.
- Brandith Irwin; Mark McPherson (1 September 2002). Your Best Face Without Surgery. Hay House, Inc. p. 129. ISBN 978-1-56170-953-3. Retrieved 29 May 2012.
- Maltoni M, Nanni O, Scarpi E, Rossi D, Serra P, Amadori D (March 2001). "High-dose progestins for the treatment of cancer anorexia-cachexia syndrome: a systematic review of randomised clinical trials". Ann. Oncol. 12 (3): 289–300. PMID 11332139.
- Lelli G, Montanari M, Gilli G, Scapoli D, Antonietti C, Scapoli D (June 2003). "Treatment of the cancer anorexia-cachexia syndrome: a critical reappraisal". J Chemother 15 (3): 220–5. doi:10.1179/joc.2003.15.3.220. PMID 12868546.
- Utian WH, Shoupe D, Bachmann G, Pinkerton JV, Pickar JH (June 2001). "Relief of vasomotor symptoms and vaginal atrophy with lower doses of conjugated equine estrogens and medroxyprogesterone acetate". Fertil. Steril. 75 (6): 1065–79. doi:10.1016/S0015-0282(01)01791-5. PMID 11384629. (the Women's Health, Osteoporosis, Progestin, Estrogen study)
- Hulley S, Grady D, Bush T, et al. (August 1998). "Randomized trial of estrogen plus progestin for secondary prevention of coronary heart disease in postmenopausal women. Heart and Estrogen/progestin Replacement Study (HERS) Research Group". JAMA 280 (7): 605–13. doi:10.1001/jama.280.7.605. PMID 9718051.