Prolactin is a globular, secreted neuroendocrine pituitary hormone present as both glycosylated and non-glycosylated monomers. The non-glycoslyated form is expressed in the pituitary gland and stored in granules prior to being secreted. The glycosylated protein reportedly has lower biologic activity but is constitutively secreted. Prolactin binds the prolactin receptor (PRLR), which has widespread expression. Prolactin is a lactogenic protein, acting mainly on the mammary gland and promoting lactation in females during pregnancy and suckling. It also has been reported to have functions related to immunoregulation, breast and prostate cancer development, and regulation of reproductive function.