PRL, along with PLs in many species, plays a central role in ensuring successful reproduction by acting after fertilization to promote a variety of developmental, metabolic, and behavioral adaptations (Fig. 9-7). Hypothalamic DA inhibits PRL secretion and is the dominant PRL regulator in mammals but not in other species. The specialization of the mammalian life cycle to include not only maternal gestation but also postpartum nurturing of offspring has been accompanied by a wide range of physiologic adaptations. Breast milk secretion in mammals, as well as milk-like secretions that occur in certain nonmammalian vertebrates, are direct responses to PRL. PRL suppression of gonadal development and sexual drive in males and females is mediated both centrally and peripherally. The physiologic actions of PRL are pathologically exaggerated in human hyperprolactinemia.