Estriol
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| Trade names | Ovestin |
| Routes of administration |
Oral, vaginal |
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| Biological half-life | 5 hours |
| Identifiers | |
| Synonyms | 16α-Hydroxyestradiol; Estra-1,3,5(10)-triene-3,16α,17β-triol |
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| ChEMBL | |
| ECHA InfoCard | 100.000.021 |
| Chemical and physical data | |
| Formula | C18H24O3 |
| Molar mass | 288.39 g·mol−1 |
| 3D model (Jmol) | |
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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.
Estriol is produced in notable quantities only during pregnancy. Levels of estriol increase 1,000-fold during pregnancy, whereas levels of estradiol and estrone increase 100-fold, and estriol accounts for 90% of the estrogens in the urine of pregnant women. At term, the daily production of estriol by the placenta is 35 to 45 mg, and levels in the maternal circulation are 8 to 13 ng/dL.
The placenta produces pregnenolone and progesterone from circulating cholesterol. Pregnenolone is taken up by the fetal adrenal glands and converted into dehydroepiandrosterone (DHEA), which is then sulfated by steroid sulfotransferase into dehydroepiandrosterone sulfate (DHEA-S). DHEA-S is hydroxylated by high CYP3A7 expression and activity into 16α-hydroxy-DHEA-S (16α-OH-DHEA-S) in the fetal liver and to a limited extent in the fetal adrenal glands. 16α-OH-DHEA-S is then taken up by the placenta. Due to high expression of steroid sulfatase in the placenta, 16α-OH-DHEA-S is rapidly cleaved into 16α-OH-DHEA. Then, 16α-OH-DHEA is converted by 3β-hydroxysteroid dehydrogenase type I (3β-HSD1) into 16α-hydroxyandrostenedione (16α-OH-A4) and 16α-OH-A4 is converted by aromatase into 16α-hydroxyestrone (16α-OH-E1), which is subsequently converted into estriol by 17β-hydroxysteroid dehydrogenase and then secreted predominantly into the maternal circulation. Approximately 90% of precursors in estriol formation originate from the fetus.
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Wikipedia