APA Dictionary of Psychology

n. a peptide hormone both synthesized and released into the bloodstream by specialized cells in the anterior pituitary gland called lactotrophs. Although generally known for its originally described role in initiating and maintaining lactation—prolactin levels rise significantly in women during pregnancy, stimulating the mammary glands to grow and subsequently produce milk—prolactin also performs many other essential reproductive, homeostatic, and behavioral functions in both sexes. These include such activities as preserving the corpus luteum and enhancing its secretion of progesterone, modulating sexual arousal and the orgasmic refractory phase, influencing spermatogenesis, regulating prostate gland development, regulating the immune response, regulating water and electrolyte concentrations (osmoregulation), modulating oligodendrocyte precursor production, and inhibiting fat metabolism. Prolactin also is associated with mammalian and avian parental behavior, with prolactin variation possibly explaining individual differences in parental choices and the initiation of parental interactions. Given such versatility of action, it is not surprising that prolactin receptors are found throughout the body, including within the hypothalamus, hippocampus, amygdala, and other areas of the central nervous system; the thymus and lymphocytes of the immune system; and the liver, kidney, prostate, testis, ovary, uterus, mammary glands, and numerous other organs. Also called lactogenic hormone; lactotropic hormone; lactotropin; luteotropic hormone (LTH); luteotropin.