Sex hormones are steroids (fat soluble compounds) that control sexual maturity and reproduction. These hormones are produced mainly by the endocrine glands. The endocrine glands in females are ovaries and those in males are testes. While both males and females have all types of hormones present in their bodies, females produce the majority of two types of hormones, estrogens and progesterone, while males produce mainly androgens such as testosterone. Most androgens produced by females are converted to estrogens and some androgens in males are also converted to estrogens. Sex hormones are synthesized from cholesterol (a fatty acid) and other compounds and secreted throughout a person's lifetime at different levels. Their production increases at puberty and normally decreases in old age.
The production of hormones is a complex process. At puberty, the brain's hypothalamus gland produces increased amounts of gonadotropin-releasing hormone. This hormone stimulates the nearby pituitary gland to release two other hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Finally, these two hormones signal the sex glands (gonads) to produce the sex hormones.
Female Reproductive Cycle
Females produce three estrogens: estradiol, estriol, and estrone. These estrogens stimulate growth of the ovaries and begin preparing the uterus for pregnancy. Estrogens also control the body's secondary sex characteristics, including breast and pelvic development and the distribution of fat and muscle. Progesterone maintains uterine conditions during pregnancy. It also acts on the central nervous system in a way that isn't yet understood.
During the monthly reproductive cycle, FSH stimulates growth of an ovarian body called the graafian follicle. The follicle encloses the egg. LH aids in the rupture of the follicle, sending the egg to the fallopian tubes. LH also promotes growth of the corpus luteum (a yellow, progesterone-secreting mass of cells that forms from an ovarian follicle after the release of a mature egg) as the ovary prepares to release the egg into the uterus.
If no pregnancy occurs within 10-12 days, the corpus luteum withers and the uterus sheds the blood supply that was formed to nourish a fetus. This shedding of the uterine lining and blood supply is called menstruation (the period). The production of estrogens and progesterone drops dramatically, and the cycle begins again.
In males, LH stimulates the development of the testes. The testes produce the androgens testosterone and androsterone. When FSH activates the testes' sperm-forming cells, testosterone maintains the process of forming sperm. This is the ten-week process results in sperm constantly ready for release by ejaculation from the penis. The androgens also promote the secondary sex characteristics of muscle growth, lowered voice range, the Adam's apple, and increased body hair.
Sex hormones were studied intensively during the 1920s. Discovery of their steroid structure and relationship to other steroids was the key to their isolation and synthesis. The first breakthroughs came in 1929 with the female hormones. American biochemist Edward Doisy (1893-1986) isolated a crystalline form of estrone. Five years later, German biochemist Adolf Butenandt (1903-) and his colleagues isolated progesterone.
In 1931, American biochemists H. L. Fevold, F. L. Hisaw, and S. L. Leonard discovered luteinizing hormone (LH) and follicle-stimulating hormone (FSH). That same year, Butenandt and Kurt Tscherning isolated the male hormones. In further male hormone developments, Swiss biochemist Leopold Ruzicka (1887-1976) soon determined the structure of testosterone. In 1934, Ruzicka partly synthesized androsterone from cholesterol, after proposing its structure. This was the first synthesis of a sex hormone and the first proof of the relationship between cholesterol and sex hormones.
Butenandt's group also showed that the sex hormones were related to cholesterol and bile acids, and in 1939 converted cholesterol into progesterone. For their work in demonstrating the structure of steroids, including the sex hormones, Ruzicka and Butenandt shared the 1939 Nobel Prize in chemistry.
Commercial synthesis came next. In the 1930s, Austrian chemists were synthesizing male and female hormones from soybean sterols (cholesterol-like substances). This process was expensive because it was hard to separate the sterols from each other. American chemist Percy Julian (1899-1975) discovered a much easier way to separate sterols, which permitted inexpensive synthesis of both progesterone and testosterone. American chemist Carl Djerassi (1923-) is also noted for synthesizing estrone and estradiol (estrogens) from plant materials.
Medical Uses of Hormones
In 1941 American surgeon Charles Huggins (1901-) was the first researcher to use chemotherapy (the chemical treatment of disease). Huggins treated prostate cancer with female sex hormones. For his work, he received the 1966 Nobel Prize in medicine. Today both male and female hormones are used to treat many kinds of cancer. Estrogen is also administered to treat menopause-related conditions and osteoporosis (the loss of bone calcium).
In addition to its use in the treatment of cancer, testosterone is administered by injection to treat men's sexual dysfunctions, such as impotence (inability to have an erection) and low sperm counts.
A synthetic progesterone called progestin was used in the first female oral contraceptive (birth control pill). The pill was developed by Americans Gregory Pincus (1903-1967), Min-Chueh Chang (1908-), and John Rock (1890-1984). Today a variety of pills containing varying amounts of progesterone and estrogen are available by prescription.