Prolactin is a hormone produced by the anterior pituitary gland, a grape-sized organ found at the base of the brain. Prolactin concentrations are regulated by dopamine (a brain chemical), and the hormone is normally present in low amounts in men and non-pregnant women. Its main role is to promote lactation (breast milk production).Prolactin concentrations are usually high throughout pregnancy and just after childbirth. During pregnancy prolactin, oestrogen and progesterone stimulate breast milk development. Following childbirth, prolactin helps initiate and maintain the breast milk supply. If a woman does not breastfeed, her prolactin concentration will soon drop back to pre-pregnancy levels. If she does breastfeed, suckling by the infant plays an important role in the release of prolactin. When the baby feeds, this has an effect on the amount of prolactin secreted by the pituitary, and this in turn controls the amount of milk produced. Prolactin concentrations will continue to be high while the mother continues to breastfeed, but will eventually fall back to pre-pregnancy levels.Besides pregnancy, the most common cause of elevated prolactin concentration is a prolactinoma, a prolactin-producing tumour of the pituitary gland. Prolactinomas are the most common type of pituitary tumour and are usually benign. They develop more frequently in women but are also found in men. Problems can arise both from the unintended affects of excess prolactin, such as milk production in the non-pregnant woman (and rarely, man) and from the size and location of the tumour.If the pituitary gland and/or the tumour enlarge significantly it can put pressure on the optic nerve, causing headaches and visual disturbances; and it can interfere with the other hormones that the pituitary gland produces. In women, prolactinomas can cause infertility and irregularities in menstruation (menstrual periods); in men, these tumours can cause a gradual loss in sexual function and desire. If left untreated, prolactinomas may eventually damage tissues surrounding them.
