Secreted mainly by anterior pituitary. Structurally homologous to growth hormone.

Stimulates milk production in breast; inhibits ovulation in females and spermatogenesis in males by inhibiting GnRH synthesis and release.- Excessive amounts of prolactin associated with ↓ libido.

Prolactin secretion is tonically inhibited by dopamine from tuberoinfundibular pathway of hypothalamus. Prolactin in turn inhibits its own secretion by ↑ dopamine synthesis and secretion from hypothalamus. TRH ↑ prolactin secretion (eg, in 1° or 2° hypothyroidism).

Dopamine agonists (eg, bromocriptine) inhibit prolactin secretion and can be used in treatment of prolactinoma.Dopamine antagonists (eg, most antipsychotics) and estrogens (eg, OCP, pregnancy) stimulate prolactin secretion.