e.hormone | hormones and the environment


Estrogens are steroid hormones made primarily in the female ovaries and the male testes in humans and other animals. Estrogens, known as the female hormones, are found in greater amounts in females than males. Phytoestrogens, which are estrogen-like compounds, are found in plants; in addition, there are compounds in the environment which can act with estrogen-like effects on plants and animals.
To see examples of estrogens, phytoestrogens, and synthetic estrogen-mimicking compounds, click on the "compounds" link on the left.
These essential molecules influence growth, development and behavior (puberty), regulate reproductive cycles (menstruation, pregnancy) and affect many other body parts (bones, skin, arteries, the brain, etc.). Estradiol is the most abundant and potent estrogen hormone. Estrone and estriol are other types of estrogens. OH and hydroxy groups extend off the carbon-based ring structures, which are referred to as "polycyclic" because they consist of several rings (cycles) attached together. Estrogen's actions were initially described by Stockard and Papanicolaou in 1917 with guinea pigs (1) and by Long and Evans in 1922 using rats (2). Both observed that pre-ovulatory follicle swelling was followed by uterine lining growth and vaginal cell maturation. Later, Allen and Doisy isolated the responsible steroid, called it estrone and described a test to detect this estrogenic activity in biological samples (3). Since then, their test, or similar ones, has become the standard way to detect, identify and characterize natural and synthetic compounds with estrogenic activity (4). Estrogen is commonly defined as "any of a family of steroid hormones that regulate and sustain female sexual development and reproductive function" (5). In this same vein, modern scientists define estrogens as materials that stimulate tissue growth by (6): * promoting cell proliferation (DNA synthesis and cell division) in female sex organs (breasts, uterus), * promoting hypertrophy, or increasing a cell's size, such as occurs in female breast and male muscle during puberty and * initiating synthesis (making) of specific proteins. Under these guidelines, any natural steroids, plant compounds or synthetic chemicals that elicit these responses in laboratory tests are considered to be estrogenic. All are not satisfied with this interpretation, however. In a recent comment, Lieberman suggests that classifying a variety of compounds as estrogens is too broad and causes confusion (4). In a response, Hughes offers to define estrogens as compounds that produce the behavior estrus ("the portion or phase of the sexual cycle of female animals characterized by willingness to accept the male"). He argues that since only true steroid compounds produce estrus, the plant and synthetic compounds that mimic other estrogenic responses are not estrogens and should be classified as something else, such as phytochemicals or environmental estrogens. In his view, "the potential importance of phytoestrogens in human health and disease is certain to derive both from their mimicry of steroidal estrogens and their failure to closely mimic the actions of steroidal estrogens." (7)