Androgen hormones

A group of hormones that stimulate the development of male sexual characteristics. Androgens are produced by specialized cells in the testes in males and in the adrenal glands in both sexes. The ovaries secrete very small quantities of androgens until the menopause. The most active androgen is testosterone, which is produced in the testes. The production of androgens by the testes is controlled by certain pituitary hormones, called gonadotrophins. Adrenal androgens are controlled by ACTH, another pituitary hormone. Androgens stimulate male secondary sexual characteristics at puberty, such as the growth of facial hair and deepening of the voice. They have an anabolic effect (they raise the rate of protein synthesis and lower the rate at which it is broken down). This increases muscle bulk and accelerates growth. At the end of puberty, androgens cause the long bones to stop growing. They stimulate sebum secretion, which, if excessive, causes acne. In early adult life, androgens promote male-pattern baldness. Androgen deficiency may occur if the testes are diseased or if the pituitary gland fails to secrete gonadotrophins. Typical effects include decreased body and facial hair, a high-pitched voice, underdevelopment of the genitalia, and poor muscle development. Overproduction of androgens may be the result of adrenal disorders (see adrenal tumours; adrenal hyperplasia, congenital), of testicular tumours (see testis, cancer of), or, rarely, of androgensecreting ovarian tumours (see ovary, cancer of). In men, excess androgens accentuate male characteristics; in boys, they cause premature sexual development. In women, excess androgens cause virilization, the development of masculine features such as an increase in body hair, deepening of the voice, clitoral enlargement, and amenorrhoea.