Estrogens are responsible for the development of female secondary sexual characteristics. Together with progesterone they control the most important female reproductive processes. The most biologically active of estrogen is 17b-estradiol.
The main actions of estradiol are: the proliferation of the endometrium, effects on the vagina and mammary gland; it also plays a role in preventing osteoporosis and cardiovascular risk reduction.
Estradiol is produced primarily in the ovary (follicle, corpus luteum), but small amounts are formed in the testes and adrenal cortex. In pregnancy estrogens are produced mainly by the placenta. Approximately 98% of the estradiol is bound to sex hormone binding globulin (SHBG = sex hormone-binding globulin).
Estradiol levels increase during the follicular phase of the menstrual cycle closely related to the growth and development of ovarian follicle. At this stage estradiol exerts a negative feedback on the pituitary, resulting in decreases in FSH levels. In the late follicular phase a dramatic increase in estradiol concentration takes place, at which the feedback becomes positive and produces a marked secretion of FSH and LH in particular, that will trigger ovulation.
After ovulation, estradiol levels initially present a marked decrease, but then increase as the corpus luteum forms. At the end of the menstrual cycle a significant decrease in estrogen levels is seen, awaiting the initiation of the next follicular phase. The level of estrogen at menopause is generally low due to diminished ovarian production.
In men estradiol is produced by the testes. Due to the increase of body fat high levels of estradiol may be recorded, due to increased peripheral aromatization of androgens. In men estradiol levels may increase with excessive consumption of marijuana, alcohol or prescribed drugs (phenothiazines and spironolactone).
Dramatic increases in estradiol can be seen both in men and women in different germ cell tumors or gonadal tumors.
Recommendations for determination of estradiol
For men: fertility disorders, diseases of the hypothalamic-pituitary-gonadal axis, gynecomastia, testicular tumors and adrenal hyperplasia.
In women: fertility disorders, disorders of the hypothalamic-pituitary-gonadal axis , gynecomastia, ovarian and adrenal hyperplasia.
Estradiol levels are used routinely to monitor ovulation during follicular stimulation for patients that are under treatment for assisted reproduction techniques.
Reference values - dependent on age and sex, and in women during their menstrual cycle, respectively pregnancy:
Conversion factors: pmol / L x 0.273 = pg / ml (ng / L); pg / ml x 3.67 = pmol / L; pg / mL = ng / L.