lactogens

Lactogens are hormones and related factors that stimulate the production and development of milk in the mammary glands. In most mammals, the principal lactogenic hormone is prolactin, a peptide produced by the anterior pituitary. Placental lactogens, produced by the placenta during pregnancy, also contribute to lactation readiness and mammary gland development. In some species, members of the growth hormone–prolactin family can have lactogenic activity, illustrating the broader concept of lactogenic signaling beyond prolactin alone.

Prolactin acts on the mammary gland through the prolactin receptor (PRLR). Binding activates intracellular pathways such as JAK2-STAT5, leading to transcription of milk-related genes and the synthesis of milk components, including caseins and lactose. Prolactin also promotes the differentiation and maintenance of milk-producing cells in the mammary alveoli. Secretion of prolactin is increased by suckling, while dopamine acts as a major inhibitory regulator; withdrawal of dopamine inhibition after birth supports lactation. Estrogen and progesterone, high during pregnancy, promote gland development but antagonize milk secretion, with lactation typically commencing after hormonal withdrawal in the postpartum period.

Placental lactogens, including human placental lactogen (hPL), are produced by the placenta and share structural similarity with prolactin and growth hormone. They support mammary gland development during pregnancy and also influence maternal metabolism to favor fetal nutrient supply. Their lactogenic effects are mediated in part through prolactin receptors and related signaling pathways.

Clinical considerations include hyperprolactinemia, which can impair reproductive function and cause galactorrhea, and insufficient prolactin signaling, which can impede lactation. Dopamine antagonists and certain pituitary disorders can alter lactogen levels and lactation. See also Prolactin and Placental lactogen.