Androgens

Androgens are a group of steroid hormones that regulate the development and maintenance of male characteristics and influence various systems in both sexes. They act by binding to the androgen receptor, a type of nuclear receptor, and modulating gene expression. In humans, the principal androgens are testosterone and its more potent derivative dihydrotestosterone (DHT). Other important androgens include androstenedione and dehydroepiandrosterone (DHEA), which can be converted into testosterone and DHT in target tissues. Androgens are synthesized mainly in the testes in males, the ovaries in females, and the adrenal cortex in both sexes; production is regulated by the hypothalamic-pituitary-gonadal axis.

Testosterone is produced by Leydig cells under luteinizing hormone control; DHT is formed from testosterone via 5-alpha-reductase in tissues such as skin and prostate. Androgens exert effects through the androgen receptor in target cells, influencing transcription and, in some cases, non-genomic signaling.

Functions: During fetal development, androgens drive male genital differentiation. At puberty they promote growth of the testes, penis, facial/body hair, voice deepening, muscle mass, and bone maturation. They influence libido and sexual function in adults, and play a role in spermatogenesis and hematopoiesis. In females, androgens contribute to pubertal development, libido, and maintenance of bone density, though at lower circulating levels.

Clinical aspects: Abnormally high or low androgen levels can cause medical problems. Hypogonadism leads to reduced secondary sexual characteristics, fertility issues, and decreased bone density; hyperandrogenism can cause acne, hirsutism, and irregular menses. Androgen receptor mutations cause androgen insensitivity syndrome. Treatments include testosterone replacement for deficiency, and antiandrogens or gonadotropin-releasing hormone agonists for conditions like prostate cancer or hormonally driven disorders.