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testosterone (tĕstŏsˈtərōn), principal androgen, or male sex hormone. One of the group of compounds known as anabolic steroids, testosterone is secreted by the testes (see testis) but is also synthesized in small quantities in the ovaries, cortices of the adrenal glands, and placenta, usually from cholesterol. Testosterone is necessary in the fetus for the development of male external genitalia; increased levels of testosterone at puberty are responsible for further growth of male genitalia and for the development and maintenance of male secondary sex characteristics such as facial hair and voice changes. Testosterone also stimulates protein synthesis and accounts for the greater muscular development of the male (see metabolism).
An abnormally low testosterone level in men, known as hypogonadism, is treated with testosterone, but it is not clear if testosterone is a safe or effective treatment for so-called low testosterone, such as the lower levels of testosterone typically found in older men. In men with lower testosterone, the level can often be raised by increasing exercise, improving diet, and reducing weight to the recommended range. For many years, synthetic steroids similar to testosterone have been used by athletes with the goal of improving performance, but medical research has shown that these drugs may have a wide range of harmful side effects and their use is now typically banned (see anabolic steroid).
(also 17 β-hydroxyandrost-4-en-3-one), the principal male sex hormone; chemically, a steroid. Testosterone occurs as colorless crystals having a melting point of 155°C. It is sparingly soluble in water but soluble in organic solvents. (The substance was first obtained in 1935. Here, testosterone in crystalline form was isolated from bovine testis tissue, 100 kg of tissue yielding 10 mg of hormone.)
In humans and other higher vertebrates, testosterone is produced by the sex glands, mainly the testes, as well as by the adrenal glands, placenta, and liver. Intermediate products in the biosynthesis of testosterone include cholesterol and progesterone.
The normal level of testosterone in the blood of a man is 0.5–0.6 microgram per 100 milliliters; in a woman, the level is 0.12 microgram per 100 milliliters. A man produces approximately 15 mg of testosterone per day. Testosterone promotes the development of male sexual organs and of secondary sex characteristics. It affects the differentiation of sexual organs and bodily structures of vertebrates developing in the uterus. The concentration of testosterone in the blood probably serves as the factor determining masculinization in males and virilism in females. Other androgens are active only after their conversion into testosterone.
Testosterone is used in medicine in substitution therapy when there are insufficiencies in the functioning of sex glands in men. It is also used for climacteric disorders in women and for certain types of tumors. Intake of testosterone over prolonged periods blocks the secretion of gonadotrophic hormones and suppresses sexual activity. In the pharmaceutical industry, the hormone is obtained from sterols and steroid saponins. Highly active synthetic analogues of testosterone, such as testosterone propionate and methyltestosterone, are used in medical practice.
REFERENCESFieser, L., and M. Fieser. Steroidy. Moscow, 1964. (Translated from English.)
Heftmann, E. Biokhimiia steroidov. Moscow, 1972. (Translated from English.)
E. P. SEREBRIAKOV