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testosterone(tĕstŏs`tərōn), principal androgen, or male sex hormonehormone,
secretory substance carried from one gland or organ of the body via the bloodstream to more or less specific tissues, where it exerts some influence upon the metabolism of the target tissue.
..... Click the link for more information. . One of the group of compounds known as anabolic steroidssteroids,
class of lipids having a particular molecular ring structure called the cyclopentanoperhydro-phenanthrene ring system. Steroids differ from one another in the structure of various side chains and additional rings. Steroids are common in both plants and animals.
..... Click the link for more information. , testosterone is secreted by the testes (see testistestis
, one of a pair of glands that produce the male reproductive cells, or sperm. In fetal life the testes develop in the abdomen, then descend into an external sac, the scrotum.
..... Click the link for more information. ) but is also synthesized in small quantities in the ovariesovary,
ductless gland of the female in which the ova (female reproductive cells) are produced. In vertebrate animals the ovary also secretes the sex hormones estrogen and progesterone, which control the development of the sexual organs and the secondary sexual characteristics.
..... Click the link for more information. , cortices of the adrenal glandsadrenal gland
or suprarenal gland
, endocrine gland (see endocrine system) about 2 in. (5.1 cm) long situated atop each kidney. The outer yellowish layer (cortex) of the adrenal gland secretes about 30 steroid hormones, the most important of which are aldosterone and
..... Click the link for more information. , and placenta, usually from cholesterolcholesterol
, fatty lipid found in the body tissues and blood plasma of vertebrates; it is only sparingly soluble in water, but much more soluble in some organic solvents. A steroid, cholesterol can be found in large concentrations in the brain, spinal cord, and liver.
..... Click the link for more information. . 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 metabolismmetabolism,
sum of all biochemical processes involved in life. Two subcategories of metabolism are anabolism, the building up of complex organic molecules from simpler precursors, and catabolism, the breakdown of complex substances into simpler molecules, often accompanied by
..... Click the link for more information. ).
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 steroidanabolic steroid
or androgenic steroid
, any of a group of synthetic derivatives of testosterone that promote muscle and bone growth. Used to treat uncontrolled weight loss in wasting diseases, anabolic steroids have also been taken by bodybuilders and athletes seeking
..... Click the link for more information. ).
(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