Estradiol is a female sex hormone that is the predominant estrogen throughout a female’s reproductive years. This hormone has a significant impact on reproductive and sexual function as well as on other organs, including the bones.

Chemistry

As a steroid hormone, estradiol is derived from cholesterol. After cleavage of the side chain and using either the delta-5 or delta-4 pathway, the key intermediary is androstenedione, part of which is converted to the male hormone testosterone. This is then converted to estradiol by an enzyme called aromatase. In another pathway, androstenedione is converted to estrone, which is then converted to estradiol.

Production and function

During the reproductive period (the onset of puberty through to menopause), much of the estradiol is produced by the granulosa cells in the ovaries through aromatization of androstenedione. The androstenedione is produced by the folliculi cells. This is then converted to estrone, which is converted to estradiol by the enzyme 17β-hydroxysteroid dehydrogenase. In men, a small amount of estradiol is produced by the testes.

As well as being produced by the gonads, in both genders fat cells produce active estradiol precursors, even in women who have gone through the menopause. Small amounts of estradiol are also produced in the brain and arterial walls.

Estradiol acts primarily as a growth hormone for the reproductive structures including the lining of the vagina, the fallopian tubes, the endometrium and the cervical glands. The hormone is also required to maintain oocytes (eggs in the ovary) and triggers a series of events that lead to ovulation. In addition, estradiol works in conjunction with progesterone to prepare the womb lining for implantation. In males, estradiol aids sperm maturation and also helps to maintain a healthy libido.