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Causes
By Mayo Clinic staff
The pituitary and your endocrine system
The pituitary gland is a small bean-shaped gland located at the base of your brain. Despite its small size, the pituitary gland influences nearly every part of your body. Its hormones help regulate important functions such as growth, blood pressure and reproduction.
The pituitary gland is part of your endocrine system, which consists of other glands that produce hormones that regulate many processes throughout your body. Besides the pituitary gland, the endocrine system includes the thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries (in females) and testicles (in men).
Pituitary tumors
Prolactinoma is one type of tumor that develops in the pituitary gland. Some pituitary tumors may produce hormones in excess (functioning pituitary tumors), but most don't (nonfunctioning pituitary tumors).
The cause of pituitary tumors remains unknown. Although these pituitary tumors are almost always noncancerous (benign), which means they don't spread to other parts of your body, they can increase in size. Because they grow in such limited space, they can compress and damage the normal pituitary tissue, interfering with hormone production. A tumor can also compress your optic nerves, slowly causing a loss of vision.
Other causes of prolactin overproduction
Overproduction of prolactin can result from causes other than a prolactinoma, including:
Medications. The secretion of prolactin in your pituitary gland normally is suppressed by the brain chemical dopamine. Drugs that block the action of dopamine in your pituitary gland or that decrease the amount of dopamine that's produced and stored in your brain may cause excess prolactin production, including:
- Tranquilizers, such as trifluoperazine and haloperidol
- Anti-nausea and gastroesophageal reflux disease (GERD) drugs, such as metoclopramide (Reglan)
- High blood pressure (hypertension) medications, such as methyldopa and reserpine.
Other pituitary tumors. Other tumors in or near your pituitary gland, such as nonfunctioning tumors and those that can cause overproduction of growth hormone (acromegaly) or the hormone cortisol (Cushing's disease), may block the flow of dopamine from your brain to your pituitary gland.
Hypothyroidism. Excess production of prolactin may occur in people with severe and long-standing hypothyroidism — insufficient hormone production by your thyroid gland.
Pregnancy, breast-feeding and breast stimulation. During pregnancy, a woman's prolactin level normally increases to prepare her breasts for milk production. After delivery, the prolactin level returns to normal, but increases again each time a baby feeds. Breast stimulation unrelated to pregnancy or breast-feeding also may cause breast discharge and a mild increase in the prolactin level.
