What Are Estrogens And Progestins?

Three steroid hormones-estrone (E1), ß-estradiol (E2), and estriol (E3)-are known collectively by their function as estrogens. Estradiol is the most physiologically physiologically active estrogen in non-pregnant women. Its potency is 12 times that of estrone and 80 times that of estriol.

In non-pregnant women, estrogens are mainly produced in the ovaries and adrenal cortex. In pregnant women, estrogens are also produced in the placenta. ß-estradiol is produced in the ovaries; estrone is synthesized in the ovaries and adrenal cortices from ß-estradiol and androstenedione; and estriol is formed in the liver by conversion of either ß-estradiol or estrone.

Progestins are comprised of progesterone and 17-alpha-hydroxyprogesterone. They exhibit similar potency. Because 17- alpha-hydroxyprogesterone is produced in minute quantities compared to progesterone, the latter is considered the most significant progestin. As is the case with estrogen, progesterone is produced in the ovaries and adrenal cortex in non-pregnant women, while in pregnant women it is also secreted in the placenta.

Both progesterone and estradiol are formed from cholesterol via progressive modification by enzymes of the steroidogenic pathways. In the luteal phase progesterone levels increase dramatically, in spite of a portion of available steroids still being converted to estrogens. Conversion of ß-estradiol to the less potent estrone or estriol diminishes circulating ß-estradiol, and further functional degradation occurs as formation of glucuronides and sulfates in the liver takes place. Similarly, progesterone is functionally degraded to less potent steroids in the liver.

During puberty, estrogens play a significant role in the maturation of such female reproductive organs as the vagina, uterus, fallopian tubes, and ovaries. Estrogens also trigger secondary sexual characteristics, namely the development of breasts and increased osteoblastic activity resulting in characteristically feminine skeletal development.

Estrogens stimulate an increase in total body protein, promoting body development during puberty. These hormones also stimulate deposition of fat in subcutaneous tissues, particularly breasts, buttocks, and thighs. Estrogens influence development of vascular function and soft textured skin and have a minor effect on pubic and underarm hair growth. Furthermore, estrogens cause a slight retention of sodium and water by the kidneys and more pronounced retention during pregnancy.

Like estrogen, progesterone plays a role in increasing the size of breasts by stimulating the development of lobules and alveoli. During the menstrual cycle, progesterone promotes secretory changes in the endometrium preparatory to the implantation of a fertilized ovum. Progesterone also has a minor effect on the retention of sodium, chloride, and water by the kidneys.

In the adult female, testosterone plays an important role in maintaining lean body mass, bone density, skin elasticity, and libido. In addition, testosterone is involved in blood cell production. Low testosterone levels have been linked to increased risk for osteoporosis, decreased lean body mass, and decreased libido, and may suggest ovarian insufficiency and/or adrenal insufficiency. Elevated testosterone levels have been linked to masculinization, hirsutism, and increased risk of insulin resistance. Elevated testosterone levels have been noted in polycystic ovary disease and adrenal hyperplasia and suggest the presence of ovarian dysfunction or adrenal dysfunction.

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