prolactin (PRL) /prōlak″tin/ [Gk, pro, before, lac, milk] , a hormone produced and secreted into the bloodstream by the anterior pituitary gland. Prolactin stimulates the development and growth of the mammary glands after the glands have been prepared by estrogen, progesterone, thyroxine, insulin, growth hormone, glucocorticoids, and human placental lactogen. After parturition, prolactin, together with glucocorticoids, is essential for the initiation and maintenance of milk production. Prolactin synthesis and release from the pituitary are mediated by the central nervous system in response to suckling by the infant. When suckling or its mechanical equivalent ceases, prolactin secretion slows and milk production ceases. Prolactin has no known function in human males. Prolactin is similar to growth hormone in its chemical structure. Prolactin excess is seen with prolactin-secreting pituitary tumors in both sexes. Also called lactogenic hormone.
