Estrogen
Estrogens (also
oestrogens) are a group of
steroid compounds, named for their importance in the
oestrus cycle, functioning as the primary
female sex hormone. While estrogens are present in both 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.
Follicle stimulating hormone (FSH) and
luteinizing hormone (LH) regulate the production of estrogen in
ovulating women. Since estrogen circulating in the blood can
feedback to reduce circulating levels of FSH and LH, some
oral contraceptives contain estrogens.
The three major naturally occurring estrogens in women are
estradiol,
estriol and
estrone. From
menarche to
menopause the primary estrogen is
estradiol 17beta. In the body these are all produced from
androgens through enzyme action. Estradiol is produced from
testosterone and estrone from
androstenedione. Estrone is weaker than estradiol, and in post-menopausal women more estrone is present than estradiol.
Estrogen is produced primarily by developing follicles in the
ovaries, the
corpus luteum and the
placenta. 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 post-
menopausal women. Synthesis of oestrogenes 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. There is evidence that a testosterone supplement can support female sexual desire (Braunstein et al, 2005). Many studies of the role of sex steroid hormones on sexual desire have been done in naturally post-menopausal women or women who have had their ovaries surgically removed. Such studies have found better correlation between sexual desire and androgen levels than for estrogen levels (Warnock et al, 2005). A clinical study found that women aged 18 to 44 who reported low sexual desire tended to have low levels of
dehydroepiandrosterone sulfate (Davis et al, 2005). Dehydroepiandrosterone is an abundant sex steroid in women and like other steroids is efficiently
sulfated. Dehydroepiandrosterone (DHEA) is a precursor steroid that can be converted to estrogens (estradiol) and androgens such as testosterone and
5α-dihydrotestosterone. Estrogens can be produced by the enzyme
aromatase which converts
androgens such as DHEA to estrogens, mainly
estradiol and
estrone.
Estriol is the third major human estrogen.
A range of synthetic and natural substances have been identified that possess estrogenic activity. These include
bisphenol-A,
phthalate esters and
nonylphenol. Estrogen replacement therapy has proven to be a very useful method of treating osteoporosis in postmenopausal women as well as the symptoms of menopause such as hot flushes, 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. Standard therapy is 0.625 mg/day of conjugated estrogens (such as is in Premarin), but the dose can range from 0.3 mg/day to 1.25 mg/day. Estrogen replacement therapy also has favorable effects on serum cholesterol levels and is claimed to dramatically reduce the incidence of cardiovascular disease. There are, however, risks associated with estrogen therapy. Among the older postmenopausal women studied as part of the
Women's Health Initiative (WHI), an orally-administered estrogen supplement has been 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 Provera as
Prempro)[
1]. Research is underway to determine if risks of estrogen supplement use are the same for all estrogen supplement types. In particular,
topically-applied estrogen may have a different spectrum of side-effects than does estrogen administered by the oral route[
2].Another very popular medical application of estrogen is the combined administration of it with
progestins in the application of oral contraceptives.Other uses include therapy involving 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.
Among people over 70 who have never smoked, women make up 85 percent of those with
chronic obstructive pulmonary disease (COPD). Mice studies suggest the possibility that COPD incidence may be tied to decreases in estrogen as women age. (Female mice that had their ovaries removed to deprive them of estrogen lost 45 percent of their working
alveoli from their lungs. Upon receiving estrogen, the mice recovered full lung function.)
Two
proteins that are activated by estrogen play distinct roles in breathing. One protein builds new alveoli, the other stimulates the alveoli to expel
carbon dioxide. Loss of estrogen hampered both functions in the test mice. (Massaro & Massaro, 2004)
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Estrogen information from the
U.S. National Library of Medicine*
Hormone Replacement Therapy*
Estrogen receptor*
Progesterone*
Progestin*
Endocrinology*
Estradiol*
Equol*
Premarin*
Equilin*
Xenoestrogen*
Phytoestrogens
