<unk>  <unk> -OH-E1), or<unk> , also known as estra-1,3,5(10)-triene-3,16α-diol-17-one, is an endogenous steroidal estrogen and a major metabolite of estrone, as well as an intermediate in the biosynthesis of estriol. It is a potent estrogen similarly to estrone, and it has been suggested that the ratio of<unk>  to 2-hydroxyestrone, the latter being much less estrogenic in comparison and even antiestrogenic in the presence of more potent estrogens like estradiol, may be involved in the pathophysiology of breast cancer. Conversely,<unk>  may help to protect against osteoporosis. In terms of relative binding affinity (RBA) for the rat uterine estrogen receptor,<unk>  showed 2.8% of the affinity of estradiol. For comparison, estrone had 11% of the affinity and estriol had 10% of the affinity of estradiol. In contrast to other estrogens, the binding of<unk>  to the estrogen receptor is reported to be covalent and irreversible.<unk>  has been reported to have 25% of the vaginal estrogenic potency of estradiol. The maximal uterotrophic and antigonadotropic effect of<unk>  was equivalent to those of estradiol and estriol, indicating that<unk>  is a fully effective estrogen. However,<unk>  was much less potent than estradiol or estrone. The C3 and C16α diacetate ester of<unk> ,<unk>  diacetate (brand names Colpoginon, Colpormon, Hormobion, and Hormocervix), has been marketed and used medically as an estrogen in Europe.
16α-Hydroxyestrone
8,9-Dehydroestrone
11-Ketoprogesterone
8,9-Dehydroestradiol
3β-Androstanediol
17α-Estradiol
3α-Androstanediol
11α-Hydroxyprogesterone