Estrogens and antiestrogens

Synthetic estrogens are a class of medications that act like natural estrogens and are mainly used for primary hypogonadism, primary amenorrhea, estrogen deficiency, and as contraceptives.

Now, antiestrogens, or estrogen antagonists include full antagonists, which antagonize natural estrogens in all tissues, and selective estrogen receptor modulators, or SERMs, which act as estrogen antagonists in some tissues but also act as estrogen agonists in others.

Full antagonists and SERMs are used for breast cancer, and SERMs are also used for osteoporosis.

But first let’s talk a bit about natural estrogen, which plays a big role in the menstrual cycle.

The hypothalamus, which is part of the brain, secretes gonadotropin-releasing hormone, or GnRH, which travels to the nearby pituitary gland and stimulates it to secrete two hormones follicle stimulating hormone, or FSH, and luteinizing hormone, or LH.

FSH and LH make the ovarian follicles, which are scattered throughout the ovaries, develop and secrete the female sex hormones, estrogens and progesterone.

These hormones gradually increase during the first 2 weeks of the cycle, called the follicular phase, but estrogen is the main hormone synthesized during this phase.

The high estrogen levels stimulate the thickening of the endometrium, the growth of endometrial glands, and the emergence of spiral arteries from the basal layer.

The high estrogen levels also make the pituitary more sensitive to the actions of hypothalamic GnRH, acting as a positive feedback signal, and at the end of the follicular phase, it leads to a massive surge of FSH and LH that leads to ovulation where one of the follicles releases an ovocyte.