Prolactin

Prolactin is a peptide hormone of the prolactin/growth hormone family produced mainly by lactotroph cells in the anterior pituitary. The human PRL gene is located on chromosome 6. Prolactin is secreted in a pulsatile fashion and exerts diverse biological effects. The primary role is to promote lactation by stimulating milk synthesis and maintaining mammary gland function after birth; prolactin also contributes to breast development during puberty and pregnancy. In addition to the pituitary, prolactin is produced by several peripheral tissues, including the decidua, immune cells, and the brain. Prolactin acts through the prolactin receptor (PRLR) expressed in many tissues, triggering JAK2/STAT5 signaling and regulating gene expression related to lactation, immunity, and metabolism.

Regulation: Prolactin release is tonically inhibited by hypothalamic dopamine; factors such as thyrotropin-releasing hormone, estrogen, suckling, sleep, stress, and exercise stimulate its secretion. Pregnancy and lactation markedly raise prolactin levels. The secretion pattern is pulsatile and influenced by circadian rhythms; half-life is relatively short, requiring continuous hypothalamic input for maintenance. Assay measurements can be affected by macroprolactin, which can cause spuriously elevated results.

Clinical aspects: Hyperprolactinemia reduces GnRH secretion and can cause ovulatory dysfunction, galactorrhea, and infertility in women, and decreased libido or hypogonadism in men. Pregnancy, stress, hypothyroidism, medications (dopamine antagonists, certain antidepressants), and pituitary tumors (prolactinomas) are common causes. Diagnosis relies on serum prolactin measurement and pituitary imaging if indicated. Treatment includes dopamine agonists such as cabergoline or bromocriptine; some tumors may require surgery or radiotherapy. Prolactin deficiency is rare and usually of pituitary/hypothalamic origin.