Epiestriol

Epiestriol.svg

Epiestriol is a steroid hormone and a minor metabolite of estriol, one of the three main estrogens produced by the human body. It is a weak estrogen and is primarily found in the urine of pregnant women.

Structure and Properties

Epiestriol, also known as 16α-hydroxy-17β-estradiol, has a chemical structure similar to that of estriol, with the primary difference being the orientation of the hydroxyl group at the 16th carbon position. This slight structural variation results in different biological activities and potencies compared to other estrogens like estradiol and estrone.

Biosynthesis

Epiestriol is synthesized in the body from estriol, which itself is derived from estrone and estradiol. The conversion involves the action of specific enzymes that hydroxylate the steroid nucleus at various positions. During pregnancy, the levels of epiestriol, along with other estrogens, increase significantly due to the enhanced activity of the placenta.

Biological Activity

As a weak estrogen, epiestriol binds to estrogen receptors but with much lower affinity compared to estradiol. It exerts mild estrogenic effects, which are important for modulating the overall estrogenic activity in the body. The precise physiological role of epiestriol is not fully understood, but it is believed to contribute to the complex hormonal milieu during pregnancy.

Clinical Significance

The measurement of epiestriol levels can be part of the assessment of fetal well-being during pregnancy. Abnormal levels of epiestriol, along with other estrogens, may indicate potential issues with the placenta or fetal development. However, it is not commonly used as a standalone diagnostic marker.

Metabolism and Excretion

Epiestriol is primarily excreted in the urine. It undergoes conjugation in the liver to form more water-soluble compounds, which are then eliminated from the body. The urinary excretion of epiestriol and other estrogens is a normal physiological process, especially during pregnancy.

See Also

• Estriol
• Estradiol
• Estrone
• Estrogen
• Steroid hormone
• Pregnancy