Description
17β – Estradiol [1, 3, 5 (10) -estratriene-3, 17β-diol; E2] is a C18 steroid hormone and an important natural estrogen.
17beta Estradiol is derived from the precursor cholesterol and belongs to the group steroid hormones called estrogens, which is present in both women and men. Estradiol is the major estrogen in the body having different functions within the human physiology throughout life. Estradiol, the most potent bioactive estrogen, is primarily synthesized from testosterone in the ovarian follicles in females, whereas in males it is produced by the testes and extraglandular conversion of androgens. Estradiol is synthesized from testosterone or estrone, a derivative of cholesterol. The main hormones responsible for advancing secondary sexual characteristics are two androgens: testosterone and dehydroepiandrosterone (DHEA), which facilitate masculine development, and estradiol, an estrogen which facilitates feminine development. Estradiol is the primary estrogen released from the gonads and other peripheral tissues. Estradiol is an important hormone present in both women and men. Estrogen deficiency in boys and in girls but especially in young girls it has an impact on puberty. The measurement of estradiol levels is useful regarding puberty to investigate if early puberty (precocious puberty) occurs in girls. Ovarian volumes increase with pubertal breast stage and correlate positively with circulating estradiol levels. [10] Amenorrhea is classified into primary and secondary amenorrhea. Primary amenorrhea is defined as the absence of menarche by the age of 14 years, while secondary amenorrhea describes the absence of menses for more than six months in previously menstruating women. In older women estrogens level should be observed in regard to menopause. Additionally, estradiol plays a role in ovulation, menstrual cycle and menopause and in this regard the function of ovaries and placenta. In addition to its role as a natural hormone, estradiol is used in the realm of hormone replacement therapy during menopause. Naturally, estradiol levels both in women and men decline with age, however, the estradiol level in older men are higher than in postmenopausal women and serve different functions in the male body (bone maturation and sex interest). Estradiol levels are related to body fat mass, bone health, affect skin metabolism and sex interest in men. Estradiol levels in men are higher than in postmenopausal women and comparable to estradiol levels in the early follicular phase. It is also worth mentioning that a correlation between testosterone and estradiol levels exists due to testosterone being the major precursor of estradiol. Additional parameters should be measured for an interpretation of the results e.g. DHEA or testosterone. In serum steroid hormones are bound to sex hormone binding globulin (SHBG) and to serum albumin, only 1 – 3 % of estradiol circulates in plasma and is present in its free form. Only this portion represents the bioactive form of the endocrine regulation.
