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Testosterone

Testosterone, also known under the systematic nomenclature as 17-hydroxyandrost-4-en-3-one, is the main circulating hormone of an androgenic type. Under the action of 5-alpha-reductase, it is converted into dihydrotestosterone, the hormone responsible for sexual differentiation. Testosterone and its metabolite, dihydrotestosterone, are the primary endogenous androgenic hormones (androgens). Endogenous androgens are responsible for the normal growth and development of the male sex organs and for development and maintenance of secondary sex characteristics. Testosterone is the major androgen in males and is controlled by luteinizing hormone (LH). LH is released from the anterior pituitary exerting the primary control on testosterone production, and acting directly on the Leydig cells in the testes, where testosterone is produced. Testosterone stimulates adult maturation of external genitalia and secondary sex organs, and the growth of beard, axillary and pubic hair. Testosterone is responsible for the development and maintenance of male sexual characteristics, including external virilization, sexual maturity at puberty, spermatogenesis, sexual behavior/libido and erectile functioning. It also supports bone and muscle tissue growth, and remains vital to ones health and well being throughout life. Testosterone is quantitatively and qualitatively the most important androgen synthesized in the body. It is formed mainly in the testicles and in small amounts in the adrenal glands and in women in the ovaries. The normal human male testes produces four to eight milligrams of testosterone daily. There is considerable variation in the reported half-life of testosterone, reported values range from 10 to 100 minutes. Circulating testosterone exhibits a diurnal variation in normal young men. After physical maturity, men often notice a slow decline in the level of testosterone produced by the body. Dubbed andropause, subnormal androgen levels can lead to a decline in muscle mass, libido, sexual functioning and overall sense of well being later in life. In many instances this indicates a need for some form of androgen replacement. Hormone replacement therapy has been used in the past to treat patients who have lost the ability to make the hormones or who have reduced hormone levels. Further, testosterone replacement therapy has been used to treat patients with abnormally low testosterone levels. The major goals of testosterone replacement therapy are to restore serum testosterone concentrations to within the normal range for healthy men and, if possible, in a way that mimics the normal circadian pattern of endogenous secretion.

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