Testosterone is a male sex hormone, one of a class of compounds known as androgens . Included in this group are testosterone, dihydrotestosterone, and androstenedione. Androgens are synthesized from cholesterol and are considered steroid hormones, a category of hormones that includes female sex hormones such as estrogen . The isolation and synthesis of testosterone were reported in 1935. Chemists Adolf Butenandt and Leopold Ruzicka later received the Nobel Prize in chemistry (in 1939) for this work and related discoveries.
Testosterone (which is also present in small amounts in females) stimulates the growth of the male reproductive organs and promotes the development of the male secondary sex characteristics. It also affects body hair distribution, baldness, voice, and skin thickness and promotes each of the following: the formation of spermatozoa, protein formation, muscle development, bone growth, the retention of calcium, the rate of basal metabolism , and the number of red blood cells in the body.
In males testosterone is manufactured and secreted overwhelmingly by the testes. After secretion, 97 percent of testosterone is bound by protein carriers in blood and circulates in the body for thirty to sixty minutes. At this point, it has either been absorbed by various tissues or degraded to inactive molecules. Much of the testosterone absorbed by tissues is reduced to dihydrotestosterone, a step that is essential for the actualization of some of testosterone's effects. Testosterone not absorbed by tissues will be degraded by the liver, and the products of this degradation will be excreted from the body.
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Hoberman, John M., and Yesalis, Charles E. (1995). "The History of Synthetic Testosterone." Scientific American 272: 76–82.