physiology

Estradiol

What is that

Estradiol (E2) is a sex hormone, the most important among human estrogens (estrone E1, estradiol E2 and estriol E3).

Typical of women during the fertile period, estradiol is produced in lower concentrations even by the male organism.

Estrone and Estradiol are interconvertible with each other, and this possibility means that in women of fertile age the ratio between E1 and E2 is approximately 1: 1.

The power of the estrone is about 12 times lower than that of the estradiol, but its biological importance is not to be underestimated, above all in the menopause. In fact, when around 50 years of age the woman ceases ovarian production of estradiol, estrone can become the dominant estrogen. During pregnancy, estriol increases, a placental steroid with very limited estrogenic activity.

Functions

In addition to intervening in sexual functions, both primary (reproductive) and secondary (breast development, etc.), estradiol influences the functionality of various organs and tissues; for example, it performs a protective action against osteoporosis and various cardiovascular diseases, contributing inter alia to the trophism of skin and hair.

Moreover, during puberty estradiol contributes to the maturation of female reproductive organs (vagina, uterus, tube, ovaries) and stimulates the appearance of secondary sexual characteristics, especially the development of the udders and the typical body conformation with deposition of fat in areas preferential (breasts, hips, thighs). The sharp decline in estrogen levels, associated with the cessation of ovarian activity, is responsible for many of the menopausal disorders.

Secretion

Menstrual cycle and Estradiol secretion

Starting from the menarche, every 28 days about a follicle is brought to maturity and during its development it secretes large quantities of estradiol, to support the growth of the uterine endometrium. Estradiol levels reach the highest level before ovulation, and then fall quite abruptly. In the luteal phase there is also a second and more contained increase in estradiol, which in synergy with the increased levels of progesterone prepares the uterus for possible implantation. There is also a feedback between the anterior pituitary and the ovary that determines the normal menstrual cycle; the low estrogenic levels, which characterize the very first phase of the cycle (menstruation), stimulate the production of FSH, which in turn induces the production of 17-b-Estradiol. This presents a preovulatory peak responsible for the ovulatory elevation of LH.

In women of reproductive age most of the estradiol is produced by the ovaries under the stimulation of adenohypophyseal hormones LH (luteinizing) and FSH (stimulating follicle): the pituitary luteinizing hormone (LH) binds to the receptors of theca cells promoting the androgen synthesis (androstenedione and testosterone), which are mostly picked up by granulosa cells and readily converted to estradiol (androstenedione can also be converted into estrone). The two cell types just mentioned belong to the ovarian follicle, that is to the structure containing the egg cell and its covering, whose outer layer is constituted by the cells of the theca, and the innermost one by the granulosa cells.

The aromatase enzyme, which converts androgens into estrogens, is not the preserve of granulosa cells; this enzyme is in fact expressed in various tissues, especially in the adipose tissue. As a result, estradiol levels are generally higher in women and in obese men than in normal weight. In addition to adipose tissue, a significant amount of estrogen is also produced by skeletal muscles, the liver and the adrenal cortex. This latter portion of estradiol becomes particularly important after menopause, a time when estrone is the main steroid with estrogenic activity.

In the bloodstream, only a small proportion of estradiol is separated from transport proteins, while most circulate closely linked to the so-called SHBG (sex hormone transport proteins), and more loosely bound to albumin. Among these fractions only the free one (about 2.2%) is biologically active, since - given its lipophilicity - it freely crosses cell membranes and interacts with its cytoplasmic receptors, regulating gene transcription and protein synthesis.

In humans, a certain amount of estradiol is produced by Leydig's testicular cells and at peripheral level. for the aforementioned intervention of the aromatase enzyme.

Values ​​and blood analysis

PREPARING THE PATIENT FOR THE EXAM:

Fasting in the 12 hours before picking.

MAIN INDICATIONS

Changes in the menstrual cycle, functioning ovarian tumors and control of patients subjected to ovulation induction and assisted fertilization.

LEVELS OF ESTRADIOLO - REFERENCE INTERVALS

Female - Follicular phase

10 - 178 pg / mL

Female - Pre-ovulatory peak

48 - 388 pg / mL

Female - Luteal phase

31 - 247 pg / mL

Female - Menopause

0 - 30 pg / mL

males

10 - 45 pg / mL

LOW EXTRADIOLO

Low levels of 17-B-estradiol may be present in the following pathological conditions:

  • hermaphroditism e
  • pseudohermaphroditism,
  • hypogonadism
  • ipogonadotropinemico,
  • adrenal hyperplasia with 21-hydroxylase block.

In women of fertile age the drop in estrogen can be caused by particularly restrictive diets, especially when associated with strenuous physical activity.

EXTRADIOLO ALTO

Elevated levels of 17-B-estradiol may be present in the following pathological conditions: estradiol-secreting ovarian tumors, testicular tumors, hepatic failure. High levels of estradiol are involved in some types of cancer, such as breast cancer and uterine lining cancer; in addition there are several benign gynecological circumstances that depend on estrogen, such as endometriosis. When men produce too much estradiol they have some female characteristics, such as the increase in breast tissue (gynecomastia).

Examples of ESTRADIOL BASED DRUGS

Climara ®, Estrofem ®, Ephelia ®