estrogen n : a general term for female steroid sex hormones that are secreted by the ovary and responsible for typical female sexual characteristics [syn: oestrogen]
Estrogens (U.S., otherwise oestrogens or œstrogens) are a group of steroid compounds, named for their importance in the estrous cycle, and functioning as the primary female sex hormone.
Estrogens are used as part of some oral contraceptives, in estrogen replacement therapy of postmenopausal women, and in hormone replacement therapy for transwomen.
Like all steroid hormones, estrogens readily diffuse across the cell membrane; inside the cell, they interact with estrogen receptors. Additionally, estrogens have been shown to activate a G protein-coupled receptor, GPR30.
Types of estrogenThe three major naturally occurring estrogens in women are estradiol, estriol, and estrone. In the body these are all produced from androgens through actions of enzymes.
Premarin, a commonly prescribed estrogenic drug, contains the steroidal estrogens equilin and equilenin, in addition to estrone sulfate. A range of synthetic and natural substances have been identified that also possess estrogenic activity. Synthetic substances of this kind are known as xenoestrogens, plant products with estrogenic activity are called phytoestrogens, and those produced by fungi are known as mycoestrogens. Unlike estrogens produced by mammals, these substances are not necessarily steroids.
Estrogen productionTestosterone is synthesized during steroidogenesis, with cholesterol as the starting molecule.
Estrogen is produced primarily by developing follicles in the ovaries, the corpus luteum, and the placenta. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) stimulate the production of estrogen in the ovaries. Some estrogens are also produced in smaller amounts by other tissues such as the liver, adrenal glands, and the breasts. These secondary sources of estrogen are especially important in postmenopausal women.
Synthesis of estrogens starts in theca interna cells in the ovary, by the synthesis of androstenedione from cholesterol. Androstenedione is a substance of moderate androgenic activity. This compound crosses the basal membrane into the surrounding granulosa cells, where it is converted to estrone or estradiol, either immediately or through testosterone. The conversion of testosterone to estradiol, and of androstenedione to estrone, is catalyzed by the enzyme aromatase.
Estradiol levels vary through the menstrual cycle, with levels highest just before ovulation.
FunctionsWhile estrogens are present in both men and women, they are usually present at significantly higher levels in women of reproductive age. They promote the development of female secondary sex characteristics, such as breasts, and are also involved in the thickening of the endometrium and other aspects of regulating the menstrual cycle. In males, estrogen regulates certain functions of the reproductive system important to the maturation of sperm and may be necessary for a healthy libido. Furthermore, there are several other structural changes induced by estrogen, in addition to other functions.
- promote formation of female secondary sex characteristics
- decelerate height growth
- accelerate metabolism (burn fat)
- reduce muscle mass
- stimulate endometrial growth
- increase uterine growth
- maintenance of vessel and skin
- reduce bone resorption, increase bone formation
- morphic change (endomorphic -> mesomorphic -> ectomorphic)
- protein synthesis
- increase hepatic production of binding proteins
- Fluid balance
- salt (sodium) and water retention
- Gastrointestinal tract
- reduce bowel motility
- increase cholesterol in bile
- Lung function
- promotes lung function by supporting alveoli (in rodents but probably in humans).
Role in cancerAbout 80% of breast cancers, once established, rely on supplies of the hormone estrogen to grow: they are known as hormone-sensitive or hormone-receptor-positive cancers. Suppression of production in the body of estrogen is a treatment for these cancers.
Medical applicationsSince estrogen circulating in the blood can negatively feed-back to reduce circulating levels of FSH and LH, most oral contraceptives contain a synthetic estrogen, along with a synthetic progestin. Even in men, the major hormone involved in LH feedback is estradiol, not testosterone.
As more fully discussed in the article on Hormone replacement therapy, estrogen and other hormones are given to postmenopausal women in order to prevent osteoporosis as well as treat the symptoms of menopause such as hot flashes, vaginal dryness, urinary stress incontinence, chilly sensations, dizziness, fatigue, irritability, and sweating. Fractures of the spine, wrist, and hips decrease by 50-70% and spinal bone density increases by ~5% in those women treated with estrogen within 3 years of the onset of menopause and for 5-10 years thereafter.
Before the specific dangers of conjugated equine estrogens were well understood, standard therapy was 0.625 mg/day of conjugated equine estrogens (such as Premarin). There are, however, risks associated with conjugated equine estrogen therapy. Among the older postmenopausal women studied as part of the Women's Health Initiative (WHI), an orally-administered conjugated equine estrogen supplement was found to be associated with an increased risk of dangerous blood clotting. The WHI studies used one type of estrogen supplement, a high oral dose of conjugated equine estrogens (Premarin alone and with medroxyprogesterone acetate as PremPro).
In a study by the NIH, esterified estrogens were not proven to pose the same risks to health as conjugated equine estrogens. Hormone replacement therapy has favorable effects on serum cholesterol levels, and when initiated immediately upon menopause reduces the incidence of cardiovascular disease. Estrogen has a protector effect on atherosclerosis : it lowers LDL and triglycerides, it raises HDL levels and has endothelial vasodilatation properties plus an anti-inflammatory component.
Research is underway to determine if risks of estrogen supplement use are the same for all methods of delivery. In particular, estrogen applied topically may have a different spectrum of side-effects than when administered orally, and transdermal oestrogens do not affect clotting as they are absorbed directly into the systemic circulation, avoiding first-pass metabolism in the liver. This route of administration is thus preferred in women with a history of thrombo-embolic disease.
Estrogen is also used in the therapy of vaginal atrophy, hypoestrogenism (as a result of hypogonadism, castration, or primary ovarian failure), amenorrhea, dysmenorrhea, and oligomenorrhea. Estrogens can also be used to suppress lactation after child birth.
Hormone-receptor-positive breast cancers are treated with drugs which suppress production in the body of estrogen. This technique, in the context of treatment of breast cancer, is known variously as hormonal therapy, hormone therapy, or anti-estrogen therapy (not to be confused with hormone replacement therapy). Certain foods such as soy may also suppress the proliferative effects of estrogen and are used as an alternative to hormone therapy.
In humans and mice, estrogen promotes wound healing.
At one time, estrogen was used to induce growth attenuation in tall girls. Recently, estrogen-induced growth attenuation was used as part of the controversial Ashley Treatment to keep a developmentally disabled girl from growing to adult size.
Under certain circumstances, estrogen may also be used in males for treatment of prostate cancer.
Most recently, estrogen has been used in experimental research as a way to treat patients suffering from bulimia nervosa, in addition to Cognitive Behavioral Therapy, which is the established standard for treatment in bulimia cases. The estrogen research hypothesizes that the disease may be linked to a hormonal imbalance in the brain.
Estrogen has also been used in studies which indicate that it may be an effective drug for use in the treatment of traumatic liver injury.
Estrogen and Mental HealthEstrogen is considered to play a significant role in women’s mental health. A conceptual model of how estrogen affects mood was suggested by Douma et al 2005 based on their extensive literature review relating activity of endogenous, bio-identical and synthetic estrogen with mood and well-being. They concluded the sudden estrogen withdrawal, fluctuating estrogen, and periods of sustained estrogen low levels correlated with significant mood lowering. Clinical recovery from depression postpartum, perimenopause, and postmenopause was shown to be affective after levels of estrogen were stabilized and/or restored..
Health risks and warning labelsThe labeling of estrogen-only products in the U.S. includes a boxed warning that unopposed estrogen (without progestagen) therapy increases the risk of endometrial cancer.
Based on a review of data from the WHI, on January 8, 2003 the FDA changed the labeling of all estrogen and estrogen with progestin products for use by postmenopausal women to include a new boxed warning about cardiovascular and other risks. The estrogen-alone substudy of the WHI reported an increased risk of stroke and deep vein thrombosis (DVT) in postmenopausal women 50 years of age or older and an increased risk of dementia in postmenopausal women 65 years of age or older using 0.625 mg of Premarin conjugated equine estrogens (CEE). The estrogen-plus-progestin substudy of the WHI reported an increased risk of myocardial infarction, stroke, invasive breast cancer, pulmonary emboli and DVT in postmenopausal women 50 years of age or older and an increased risk of dementia in postmenopausal women 65 years of age or older using PremPro, which is 0.625 mg of CEE with 2.5 mg of the progestin medroxyprogesterone acetate (MPA).
Estrogens in cosmeticsSome hair shampoos on the market include estrogens and placental extracts; others contain phytoestrogens. There are case reports of young children developing breasts after exposure to these shampoos. These products are often marketed to African-American consumers.
On September 9, 1993, the FDA determined that not all topically-applied hormone-containing drug products for OTC human use are generally recognized as safe and effective and are misbranded. An accompanying proposed rule deals with cosmetics, concluding that any use of natural estrogens in a cosmetic product makes the product an unapproved new drug and that any cosmetic using the term "hormone" in the text of its labeling or in its ingredient statement makes an implied drug claim, subjecting such a product to regulatory action.
In addition to being considered misbranded drugs, products claiming to contain placental extract may also be deemed to be misbranded cosmetics if the extract has been prepared from placentas from which the hormones and other biologically active substances have been removed and the extracted substance consists principally of protein. The FDA recommends that this substance be identified by a name other than "placental extract" and describing its composition more accurately because consumers associate the name "placental extract" with a therapeutic use of some biological activity.
External links and further reading
- Nussey and Whitehead: Endocrinology, an integrated approach, Taylor and Francis 2001. Free online textbook.
estrogen in Arabic: إستروجين
estrogen in Bulgarian: Естроген
estrogen in Catalan: Estrogen
estrogen in Czech: Estrogen
estrogen in Danish: Østrogen
estrogen in German: Estrogene
estrogen in Dhivehi: އެސްޓްރަޖަން
estrogen in Estonian: Östrogeenid
estrogen in Modern Greek (1453-): Οιστρογόνο
estrogen in Spanish: Estrógeno
estrogen in Persian: استروژن
estrogen in Faroese: Østrogen
estrogen in French: Œstrogène
estrogen in Korean: 에스트로겐
estrogen in Croatian: Estrogeni
estrogen in Indonesian: Estrogen
estrogen in Icelandic: Estrógen
estrogen in Italian: Estrogeno
estrogen in Hebrew: אסטרוגן
estrogen in Lithuanian: Estrogenai
estrogen in Macedonian: Естрогени хормони
estrogen in Dutch: Oestrogeen
estrogen in Japanese: エストロゲン
estrogen in Norwegian: Østrogen
estrogen in Occitan (post 1500): Estrogèn
estrogen in Polish: Estrogeny
estrogen in Portuguese: Estrogênio
estrogen in Russian: Эстрогены
estrogen in Sundanese: Éstrogén
estrogen in Finnish: Estrogeeni
estrogen in Swedish: Östrogen
estrogen in Vietnamese: Estrogen
estrogen in Chinese: 雌激素