Structure of 2-hydroxyestradiol, a<unk> . A<unk>  is a steroidal estrogen that contains<unk>  (1,2-dihydroxybenzene) within its structure. The<unk> s are endogenous metabolites of estradiol and estrone and include the following compounds: * 2-Hydroxylated: * 2-Hydroxyestradiol * 2-Hydroxyestrone * 2-Hydroxyestriol * 4-Hydroxylated: * 4-Hydroxyestradiol * 4-Hydroxyestrone * 4-Hydroxyestriol The most abundant<unk>  in serum and urine is 2-hydroxyestrone, with 2-hydroxyestradiol and 2-hydroxyestriol also being formed, while the principal 4-hydroxy<unk> , 4-hydroxyestrone, is present in only small amounts in urine. 4-Hydroxyestriol has been detected in the urine of pregnant women. The<unk> s are formed from estradiol and estrone by cytochrome P450 enzymes predominantly in the liver but also in extrahepatic tissues, and are metabolized by<unk>  O-methyltransferase (COMT) into methoxylated estrogens such as 2-methoxyestradiol and 4-methoxyestrone as well as by conjugation via other phase II enzymes. Under poor conditions of inactivation by phase II enzymes,<unk> s can undergo oxidation to reactive quinones and semiquinones, and this has been hypothesized to contribute to estrogen-induced carcinogenesis. Similarly to estradiol and estrone,<unk> s possess estrogenic activity. 2-Hydroxylated<unk> s are weak and possibly antiestrogenic estrogens, whereas their 4-hydroxylated counterparts are more potent in their estrogenic activity. For instance, 2-hydroxyestrone reportedly shows negligible uterotrophic effect in animals, whereas 4-hydroxy<unk> s show moderate changes in stimulating uterine weight. In addition to being substrates for COMT similarly to<unk> amines like dopamine, norepinephrine, and epinephrine,<unk> s are potent competitive inhibitors of COMT as well as of tyrosine hydroxylase, and may affect both<unk> amine biosynthesis and metabolism.
Catechol estrogen
Progestogen 
Progestogen
Progestogen ester
Estradiol dienantate
17β-Aminoestrogen
17α-Methylprogesterone
Hysterothylacium