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|Appearance:||White Powder||Synonyms:||16α-Hydroxyestradiol; Estra-1,3,5(10)-triene-3,16α,17β-triol|
active pharmaceuticals ingredients,
active pharma ingredients
USP Grade Estriol Active Pharmaceutical Ingredient CAS: 50-27-1
Estriol (E3), or oestriol, also known as 16α-hydroxyestradiol or as estra-1,3,5(10)-triene-3,16α,17β-triol, is a natural steroidal estrogen and one of the three main estrogens in the human body.Production of estriol by the ovaries is almost undetectable in non-pregnant women. However, during pregnancy, estriol is synthesized in very high amounts by the placenta and is by far the most produced estrogen in the body,although circulating levels are similar to those of other estrogens due to a relatively high rate of metabolism and excretion.
Mechanism of action
Similarly to estradiol and estrone, estriol binds to and acts as an agonist of both of the estrogen receptors (ER), ERα and ERβ The affinities of estriol for the ERα and ERβ relative to those of estradiol are 14% and 21%, respectively. As such, unlike estradiol (and estrone), estriol has preferential affinity for ERβ.However, estriol is described as a relatively weak estrogen and has mixed agonist-antagonist activity at the ER; on its own, it is weakly estrogenic, but in the presence estradiol, it is antiestrogenic. Relative to estradiol, estriol has 80-fold lower estrogenic potency while estrone has 12-fold lower estrogenic potency.
Estriol also acts as an antagonist of the GPER, where, conversely, estradiol acts as an agonist.Estradiol increases breast cancer cell growth via activation of the GPER (in addition to the ER), and estriol has been found to inhibit estradiol-induced proliferation of triple-negative breast cancer cells through blockade of the GPER.
Estriol is marketed widely in Europe and elsewhere throughout the world under the brand names Ovestin, Ortho-Gynest, and a variety of others. It is available in oral tablet, vaginal cream, and vaginal suppository form, and is used in hormone replacement therapy for menopausal symptoms. Estriol is also available in some countries as estriol succinate (brand name Synapause), a dosage-equivalent ester prodrug of estriol. Estriol and estriol succinate are not approved for use in the United States and Canada, although they have been produced and sold by compounding pharmacies in North America for use as a component of bioidentical hormone replacement therapy. In addition, topical creams containing estriol are not regulated in the U.S. and are available over-the-counter.
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