androgen

An androgen is any member of a group of steroid hormones that regulate the development and maintenance of male characteristics. The principal androgen in humans is testosterone, produced mainly by the testes in males, with smaller amounts from the adrenal glands and, in females, from the ovaries and adrenals. Dihydrotestosterone (DHT) is a more potent metabolite formed from testosterone by 5-alpha reductase. Other androgens include androstenedione and dehydroepiandrosterone (DHEA).

Androgens are synthesized from cholesterol through steroidogenesis in the Leydig cells of the testes, the ovarian theca cells, and the adrenal cortex. They act by binding to the androgen receptor (AR), a nuclear receptor that regulates gene transcription. The AR–ligand complex binds to androgen response elements in DNA to control expression of genes involved in development and metabolism. Testosterone can be locally converted to DHT in target tissues, which often strengthens androgenic effects.

Physiological roles include the development of male primary and secondary sex characteristics, stimulation of spermatogenesis, and maintenance of muscle and bone mass. Androgens also influence behavior and libido. In females, androgens contribute to ovarian function and sexual drive, and affect hair growth and sebaceous gland activity. Regulation occurs through the hypothalamic-pituitary-gonadal axis, with negative feedback from testosterone modulating GnRH, LH, and FSH secretion.

Clinical aspects cover hypogonadism with low testosterone, androgen insensitivity syndrome due to AR mutations, and conditions of androgen excess such as polycystic ovary syndrome. Androgen deprivation therapy is used for prostate cancer. Exogenous androgens or anabolic steroids carry risks of adverse effects. Measurement typically includes serum total and free testosterone and related steroids, with consideration of diurnal variation and age.