Prolactin is a hormone released from the anterior pituitary gland that stimulates milk production in the breast. Hyperprolactinemia, or high blood prolactin, is normal in pregnancy because milk production is necessary for the nursing of a newborn. Besides pregnancy, other causes of hyperprolactinemia are abnormal. Dopamine, a neurotransmitter, or signaling molecule used for communication between brain cells, also plays a role in the regulation of prolactin.
Dopamine Studies
According to a 2001 "Endocrine Reviews" study, the interaction of dopamine with its Type 2 receptors in the brain suppresses the actions of brain cells that release prolactin. As a result, dopamine is also referred to as prolactin inhibiting hormone. Dopamine agonists, or medications that stimulate Type 2 dopamine receptors, also cause a decrease in prolactin levels, which makes them helpful when levels of natural dopamine are low, such as in Parkinson's disease. If you have Parkinson's disease, your blood prolactin levels will also be elevated due to low levels of dopamine.
Excess Prolactin
Hyperprolactinemia, or excess prolactin in the blood, interferes with functions of the reproductive systems in both sexes. In females, hyperprolactinemia inhibits the development of eggs in the ovaries, thereby resulting in loss of menstrual cycle and fertility. In males, hyperprolactinemia inhibits the production of sperm and testosterone, resulting in a low sex drive, erectile dysfunction and infertility. Also in males, there is increased development of breasts, and frequent discharge of milk from the nipples.
Conditions That Result in Abnormal Hyperprolactinemia
Prolactin may be abnormally increased if you have a brain tumor, such as a pituitary tumor. But, according to the 2001 "Endocrine Reviews" study, pituitary tumors often do not result in hyperprolactinemia because most are small and confined to a region of the pituitary gland. Other causes of abnormal hyperprolactinemia include hypothyroidism, Parkinson's disease, antiemetics -- or medications that prevent vomiting, renal failure and liver failure. Stress may also elevate prolactin levels in the blood.
Tests and Management of Hyperprolactinemia
When a pituitary tumor is suspected as the cause for abnormal hyperprolactinemia, an MRI of the brain should be taken. If your visual fields are disrupted, it may be due to a pituitary tumor, so it is therefore also useful to examine the visual fields when pituitary tumors are suspected. These tumors that cause abnormal hyperprolactinemia are treated based on their size, associated symptoms and the presence of visual field defects. Treatment is only considered when symptoms such as headaches and sexual dysfunction are present. Small pituitary tumors are treated with Type 2 dopamine agonists such as bromocriptine and cabergoline. These drugs suppress prolactin secretion by stimulating dopamine receptors. When pituitary tumors are large enough to cause visual field defects, a surgical procedure is required.
References
- "Endocrine Reviews"; Dopamine as a Prolactin Inhibitor; Nira Ben-Jonathan and Robert Hnasko; December 2001
- "Pocket Medicine"; Hyperpituitary Syndromes; Marc S. Sabatine M.D., M.P.H.; 2004
