noun, plural: estradiol
An estrogenic hormone with a chemical formula of C18H24O2; a potent estrogen; a major female sex hormone in being largely involved in the regulation of the estrous and menstrual reproductive cycles in females
Estradiol (E2) is one of the major endogenous estrogens of humans and other vertebrates. Other endogenous estrogens are estrone (E1), estriol (E3), and estetrol (E4). Estradiol is an estrogenic hormone with a chemical formula of C18H24O2. Estradiol is produced naturally in the gonads and possibly in the adrenal cortex and other tissues. In females, the estradiol is produced mainly in the maturing Graafian follicle of the ovary. It is also produced in the placental tissues during pregnancy. The biosynthesis of estradiol begins with the use of cholesterol as the initial metabolite. Series of enzymatic steps lead to the production of androstenedione. The androstenedione is converted into estrone through the catalytic action of aromatase. Estrone, in turn, is transformed reversibly into estradiol through the action of the enzyme, 17β-hydroxysteroid dehydrogenase. This occurs in various tissues, e.g. in liver, mammary glands, and uterus.
Apart from esterone, testosterone can also be converted into estradiol through aromatization. The process though is irreversible and makes use of aromatase, the enzyme that catalyzes the conversion of testosterone into estradiol.
Estradiol is regarded as the major female sex hormone. It is involved in the development of female secondary sexual characteristics. It promotes widening of the hips, development of the breasts, etc. It is also a key player in the regulation of the estrous and the menstrual reproductive cycles in females. For instance, it promotes the proliferation and the thickening of the tissues and blood vessels in the endometrium. Estradiol is also important in the development and the maintenance of female reproductive tissues, e.g. uterus and mammary glands.
Estradiol is also produced in males. However, the quantity is relatively lower in males than in females. Estradiol is produced mainly by the Leydig cells of the testis. It may also be produced by Sertoli cells and other germ cells, as well as in brain, liver, bone, and adipose tissues. In both males and females, estradiol is involved in the mediation of pubertal growth spurt and epiphyseal closure. Apart from vertebrates, certain crustaceans, insects, etc. are said to produce estradiol.
Estradiols are released into the bloodstream to reach target cells. Inside the target cell, the estradiol binds strongly to estrogen receptors. The estradiol is the major agonist of the estrogen receptors, ERα and ERβ. The binding leads to the transcription and the expression of certain genes.
Estradiol is also produced synthetically. It can be obtained from the urine of pregnant women or from ergosterol. In its commercial form, it is used as a medication to correct estrogen levels in patients with estrogen deficiency. It is also used in breast cancer treatments.