Prolactin is a hormone secreted by the anterior portion of the pituitary gland (sometimes called the "master gland"). Its role in the male has not been demonstrated, but in females, prolactin promotes lactation, or milk production, after childbirth.
The prolactin test is used to diagnose pituitary dysfunction that might be caused by a tumor called an adenoma. In some circumstances, the test is also used to evaluate absence of menstrual periods (amenorrhea), or spontaneous production of milk (galactorrhea) by a woman who is not pregnant or lactating.
Prolactin is also known as the lactogenic hormone or lactogen. It is essential for the development of the mammary glands for lactation during pregnancy, and for stimulating and maintaining lactation after childbirth. Like the human growth hormone, prolactin acts directly on tissues, and its levels rise in response to sleep and to physical or emotional stress. During sleep, prolactin levels can increase to the circulating levels found in pregnant women (as high as ten to twenty times the normal level).
Prolactin secretion is controlled by prolactin-releasing and prolactin-inhibiting chemicals (factors) secreted by an area of the brain called the hypothalamus. Another hormone, thyroid-releasing hormone, or TRH, can also stimulate prolactin.
Tumors of the pituitary, called adenomas, are the most common cause of excessive levels of prolactin. Depending on the type of cell involved, these tumors are also called prolactin-secreting pituitary acidophilic or chromophobic adenomas. Moderately high prolactin levels are found to a lesser extent in women with secondary amenorrhea, galactorrhea, low thyroid, anorexia, and a disorder known as polycystic ovary syndrome, a disease whose cause is not well-known.
Because high prolactin levels are more likely due to pituitary adenoma than other causes, the prolactin level is used to diagnose and monitor this type of tumor. Several stimulation and suppression tests, with TRH or levodopa, respectively, have been designed to differentiate pituitary adenoma from other causes of prolactin overproduction.
Janis O. Flores, The Gale Group Inc., Gale, Detroit,