Estriol/[email protected]

Estriol (also oestriol or E3) is one of the three main estrogens produced by the human body.

Estriol is only produced in significant amounts during pregnancy as it is made by the placenta from 16-hydroxydehydroepiandrosterone sulfate (16-OH DHEAS),an androgen steroid made in the fetal liver and adrenal glands.

The human placenta produces pregnenolone and progesterone from circulating cholesterol. Pregnenolone is converted in the fetal adrenal gland into dehydroepiandrosterone (DHEA), a C19 steroid, then subsequently sulfonated to dehydroepiandrosterone sulfate (DHEAS). DHEAS is converted to 16-OH DHEAS in the fetal liver. The placenta converts 16-OH DHEAS to estriol, and is the predominant site of estriol synthesis.

Levels of estriol in non-pregnant women do not change much after menopause, and levels are not significantly different from levels in men.

In pregnant women with multiple sclerosis, estriol reduces the disease's symptoms noticeably,according to researchers at UCLA's Geffen Medical School.

Estriol can be a weak or strong estrogen depending on if it is given acutely or chronically when given to immature animals, but is an antagonist when given in combination with estradiol.Estriol may play a role in the development of breast cancer, but based on in vitro research, does appear to act as an antagonist to the G-protein coupled estrogen receptor.Though estriol is used as part of the primarily North American phenomenon of bioidentical hormone replacement therapy, it is not approved for use by the FDA or Health Canada. Though initial research in the 1970s suggested it could be used therapeutically as an estrogen, subsequent research failed to confirm this hypothesis.