The pituitary hormone (see PITUITARY GLAND) which initiates lactation (the production of breast milk). If lactation does not occur in a woman who has just given birth, or fails, it may be started by injection of prolactin.

The secretion of prolactin is normally inhibited by the secretion of DOPAMINE by the HYPOTHALAMUS into the portal capillaries of the pituitary stalk to reach the anterior pituitary cells. Drugs that deplete the brain stores of dopamine or antagonise dopamine at receptor level will cause HYPERPROLACTINAEMIA so may result in the secretion of milk from the breast and AMENORRHOEA. METHYLDOPA depletes brain stores of dopamine and the PHENOTHIAZINES act as dopamine antagonists at receptor level. The most common cause of hyperprolactinaemia is a pituitary tumour. These may be minute and are then called microadenomas, or may actually enlarge the pituitary fossa and are then called macroadenomas. The patient may present with infertility – because patients with hyperprolactinaemia do not ovulate – or with amenorrhoea and even GALACTORRHOEA.

BROMOCRIPTINE is a dopamine agonist. Treatment with bromocriptine therefore controls hyperprolactinaemia, restoring normal menstruation and ovulation and suppressing galactorrhoea. If the cause of hyperprolactinaemia is an adenomatous growth in the pituitary gland, surgical treatment might be offered.