hormoneprolactin

Prolactin is a peptide hormone produced by the anterior pituitary gland's lactotroph cells. In humans it is encoded by the PRL gene and secreted as a single-chain polypeptide of approximately 199 amino acids, with several glycosylated isoforms that influence its half-life. Prolactin receptors (PRLR) are widely distributed, including in the mammary gland, hypothalamus, immune cells, and various other tissues, enabling a broad range of physiological actions.

Its best-known role is to promote lactation: prolactin stimulates milk protein synthesis and mammary gland development during pregnancy, and maintains lactation after birth. Critically, milk ejection is driven by oxytocin, while prolactin drives production. Beyond lactation, prolactin participates in reproductive regulation, immune modulation, osmoregulation, metabolism, and neurobehavioral processes, with PRLR signaling influencing glandular function, immune cell activity, and neuroendocrine interactions.

Secretion is tightly controlled by hypothalamic signals. Dopamine acting through D2 receptors inhibits PRL release, generating tonic suppression; suckling, stress, and some estrogens can relieve this inhibition and raise prolactin. Thyrotropin-releasing hormone and estrogen can also stimulate PRL release. PRL displays pulsatile secretion with circadian variation, often peaking during sleep.

Clinical significance: excess prolactin (hyperprolactinemia) can cause galactorrhea, menstrual disturbances, and infertility in women and reduced libido or hypogonadism in men. Causes include pituitary adenomas (prolactinomas), hypothalamic disease, and medication effects (notably dopamine antagonists). Treatments include dopamine agonists such as cabergoline or bromocriptine; surgical or radiotherapeutic options for resistant cases. Low prolactin levels can indicate pituitary damage or certain metabolic conditions.