Pituitary and Brain Actions of Estrogen and Progesterone in the Regulation of Primate Prolactin Secretion

Menstrual Cycle and Pregnancy. The anterior pituitary hormone, prolactin, has important functions in mammalian reproduction. It stimulates the production of milk proteins by epithelial cells in the mammary gland for infant nourishment.1 Prolactin may also contribute to the absence of ovulation that occurs with consistent nursing.2 Included in the 80 or so other functions attributed to prolactin across the vertebrate phyla,3 is stimulation of the immune system.4 While the immune action is manifested in males as well as females, study of the steroid regulation of pituitary prolactin has focused largely on the actions of estrogen (E) and progesterone (P) in females.