Actions of Estrogens

1. The most general effect of the estrogens is to promote tissue growth. It is more pronounced in the accessory sex tissues. Estrogens stimulate cell division in the ' deeper parts of the skin and causes a more rapid replacement of the outer cornified layers of the skin. There is some evidence that high levels of estrogens (under pathological conditions) may be potentially dangerous as they may encourage the formation of cancer in certain individuals.
2. Estrogens are required for the maintenance of vaginal lining and uterine growth. It has been observed that in the experimental animals deprived of estrogens, the vaginal lining and the uterine wall become thin, and mitotic divisions seldom occur in these tissues. Administration of estrogens to the estrogen-deprived animals causes rapid growth of the vaginal and the uterine tissue. The metabolic activity of these tissues also increases as evidenced by augmented uptake of water and electrolytes by the tissues and rise in the RNA content of the tissue.
3. Estrogens are essential for the anatomic preparation of the mammary glands for milk secretion. In some species it affects mammary development in combination with progesterone. But in some species, estrogens alone or progesterone alone produce the effect. As a general rule, the mammary glands require pre-treatment with estrogens before the progestogens are effective.
4. In mammals sexual receptivity or heat coincides with a period during which the ovaries are secreting large amounts of estrogens. Full mating behaviour generally depends upon both estrogen and progesterone. These ovarian hormones probably act through the central nervous system (hypothalamus) to condition the psychic manifestations such as increased spontaneous activity, lordosis, sexual receptivity etc.