Understanding prolactin and the prolactin test Prolactin is produced by the pituitary gland in the brain. It’s also known as PRL or lactogenic hormone. Prolactin is mainly used to help women produce milk after childbirth. It’s important for both male and female reproductive health. The specific function of prolactin in men is not well-known. However, prolactin levels have been used to measure sexual satisfaction in both men and women. A prolactin level test can reveal other issues caused by the hormone. Find an obstetrician, gynecologist, or endocrinologist near you. » Women with prolactinoma symptoms may need the test. Prolactinoma is a noncancerous tumor on the pituitary gland that produces high levels of prolactin. Symptoms of prolactinoma in women include:
The test is usually performed on people with prolactinoma to keep track of the tumor’s response to treatment. In addition, the prolactin test may be needed if you’re having fertilityproblems or irregular periods. The test can also rule out other pituitary gland or hypothalamus problems. MenMen may need the test if they display symptoms of prolactinoma. Symptoms of prolactinoma in men include: The test may also be used to:
A prolactin test is just like a blood test. It takes a few minutes at your doctor’s office or in a lab. You don’t need to prepare for it. The sample is typically collected three to four hours after waking up in the morning. Blood is drawn from a vein in your arm. There’s very little pain. You may only feel a slight pinch when the needle goes in and some mild soreness afterward. Some birth control pills, high blood pressure drugs, or antidepressants can affect the test results. Tell your doctor about any medications you’re taking before the test is done. Sleeping problems, high stress levels, and strenuous exercise before the test can also influence the results. The prolactin test carries little risk of complications. You might get a small bruise at the puncture site after blood is drawn. Keep pressure on the site for a few minutes after the needle is removed to help reduce bruising. You may feel faint or lightheaded. In rare cases, the vein can become inflamed after the test, in a condition known as phlebitis. Treat phlebitis with a warm compress applied to the site several times a day. You may face continued bleeding if you have a bleeding disorder. Also, if you’re taking blood-thinning medications like aspirin or warfarin, tell your doctor before the test is performed. Your doctor will assess whether your results are normal based on many factors, including your general health. Prolactin values can vary slightly among different labs. Normal results usually look like the following (ng/mL = nanograms per milliliter): Low levels of prolactin are usually not a concern in women or men. However, very high levels of prolactin, known as hyperprolactinemia, can indicate a deeper issue. About 10 percent of the population has hyperprolactinemia. High levels of prolactin are normal during pregnancy and after childbirth during nursing. However, hyperprolactinemia can also be caused by anorexia nervosa, liver disease, kidney disease, and hypothyroidism. Hypothyroidism can cause enlargement of the pituitary gland, which is treatable with thyroid hormone replacement therapy. High levels of prolactin can also be caused by pituitary tumors. These tumors can be treated medically or surgically. Certain medications can cause high prolactin levels. Psychiatric drugs such as risperidone and haloperidol can increase your levels. Metoclopramide can also raise your prolactin levels. This medication is normally used to treat acid reflux or nausea caused by cancer drugs. Some common stressors can also raise prolactin levels. These stressors include low blood sugar, strenuous exercise activities, and even mild forms of discomfort. If you find out that your prolactin levels are high, you may need to find ways to reduce your stress and keep your blood sugar at consistent levels. Red clover, fenugreek, or fennel can raise your prolactin levels. Avoid eating anything with these ingredients if you find out you have high prolactin levels. In some cases, high prolactin levels can lead to infertility. Prolactinoma tumors can put pressure on your pituitary gland and stop the production of hormones. This condition is known as hypopituitarism. In men, this causes a lower sex drive and a loss of body hair. In women, it can lead to infertility. Hyperprolactinemia can make it difficult for a woman to get pregnant. High prolactin levels can interrupt the normal production of the hormones estrogen and progesterone. This can cause the ovaries to release eggs irregularly or stop altogether. Medications and other prolactinoma treatments help restore fertility in most women. If you find out you have high prolactin levels or prolactinoma tumors, talk to your doctor right away about treatments. You can also ask about removing or reducing tumors. Dopamine agonists such as bromocriptine (Parlodel and Cycloset) are the most common treatment for high levels of prolactin. These medications help the brain produce dopamine to control high prolactin levels. They can also shrink prolactinoma tumors. Your doctor may recommend that you take cabergoline. Cabergoline is a newer prolactinoma treatment with milder side effects than other common prolactinoma medications. Talk to your doctor about cabergoline if you face severe side effects from other treatments, including bromocriptine. Not everyone’s prolactin levels will respond well to dopamine agonists. Your doctor may suggest radiotherapy if those medications don’t help your prolactin levels or prolactinoma. Your doctor may suggest surgery if medication doesn’t shrink your tumor. Surgery can be performed through the nose or the upper skull. Surgery and medication together can bring your prolactin levels back to normal. Other steps you can take to lower your prolactin levels include:
Vitamin B-6 is part of the dopamine production process, and higher levels can reduce prolactin levels. Vitamin E naturally prevents rises in prolactin levels. Talk to your doctor or nutritionist before changing your intake of vitamins or other supplements. Read more about the B vitamins » Your doctor will likely refer you to an endocrinologist if you have a condition related to high prolactin levels. An endocrinologist can help guide you through treatment or surgeries. Your doctor may request an MRI scan to check if a prolactinoma tumor is causing your prolactin levels to rise. Your doctor will prescribe medication to shrink any existing tumor. Sometimes there’s no specific cause for your high prolactin levels. This is known as idiopathic hyperprolactinemia. It usually goes away without treatment after several months. If your prolactin levels do not go down, your doctor will likely prescribe medication. It’s possible to get pregnant while you receive treatment for high prolactin levels. If this happens, tell your doctor or endocrinologist right away. They may tell you to stop taking your medication. However, don’t stop taking your medication until you’re told to do so. Prolactinoma and hyperprolactinemia are not life-threatening. The worst side effects of medications usually go away after treatment. Infertility caused by high prolactin levels can be reversed once prolactin levels return to normal. Your quality of life will remain high even if you need long-term treatment.
Prolactin is a single-chain protein hormone closely related to growth hormone. It is secreted by so-called lactotrophs in the anterior pituitary. It is also synthesized and secreted by a broad range of other cells in the body, most prominently various immune cells, the brain and the decidua of the pregnant uterus. Prolactin is synthesized as a prohormone. Following cleavage of the signal peptide, the length of the mature hormone is between 194 and 199 amino acids, depending on species. Hormone structure is stabilized by three intramolecular disulfide bonds. Physiologic Effects of ProlactinThe conventional view of prolactin is that its major target organ is the mammary gland, and stimulating mammary gland development and milk production pretty well define its functions. Such a picture is true as far as goes, but it fails to convey an accurate depiction of this multifunctional hormone. It is difficult to point to a tissue that does not express prolactin receptors, and although the anterior pituitary is the major source of prolactin, the hormone is synthesized and secreted in many other tissues. Overall, several hundred different actions have been reported for prolactin in various species. Some of its major effects are summarized here. Mammary Gland Development, Milk Production and Reproduction In the 1920's it was found that extracts of the pituitary gland, when injected into virgin rabbits, induced milk production. Subsequent research demonstrated that prolactin has two major roles in milk production:
The critical role of prolactin in lactation has been confirmed in mice with targeted deletions in the prolactin gene. Female mice that are heterozygous for the deleted prolactin gene (and produce roughly half the normal amount of prolactin) show failure to lactate after their first pregnancy. Prolactin also appears important in several non-lactational aspects of reproduction. In some species (rodents, dogs, skunks), prolactin is necessary for maintainance of corpora lutea (ovarian structures that secrete progesterone, the "hormone of pregnancy"). Mice that are homozygous for an inactivated prolactin gene and thus incapable of secreting prolactin are infertile due to defects in ovulation, fertilization, preimplantation development and implantation. Finally, prolactin appears to have stimulatory effects in some species on reproductive or maternal behaviors such as nest building and retrieval of scattered young. Effects on Immune Function The prolactin receptor is widely expressed by immune cells, and some types of lymphocytes synthesize and secrete prolactin. These observations suggest that prolactin may act as an autocrine or paracrine modulator of immune activity. Interestingly, mice with homozygous deletions of the prolactin gene fail to show significant abnormalities in immune responses. A considerable amount of research is in progress to delineate the role of prolactin in normal and pathologic immune responses. It appears that prolactin has a modulatory role in several aspects of immune function, but is not strictly required for these responses. Control of Prolactin SecretionIn contrast to what is seen with all the other pituitary hormones, the hypothalamus tonically suppresses prolactin secretion from the pituitary. In other words, there is usually a hypothalamic "brake" set on the lactotroph, and prolactin is secreted only when the brake is released. If the pituitary stalk is cut, prolactin secretion increases, while secretion of all the other pituitary hormones fall dramatically due to loss of hypothalamic releasing hormones. Dopamine serves as the major prolactin-inhibiting factor or brake on prolactin secretion. Dopamine is secreted into portal blood by hypothalamic neurons, binds to receptors on lactotrophs, and inhibits both the synthesis and secretion of prolactin. Agents and drugs that interfere with dopamine secretion or receptor binding lead to enhanced secretion of prolactin. In addition to tonic inhibition by dopamine, prolactin secretion is positively regulated by several hormones, including thyroid-releasing hormone, gonadotropin-releasing hormone and vasoactive intestinal polypeptide. Stimulation of the nipples and mammary gland, as occurs during nursing, leads to prolactin release. This effect appears to be due to a spinal reflex arc that causes release of prolactin-stimulating hormones from the hypothalamus. Estrogens provide a well-studied positive control over prolactin synthesis and secretion. The increasing blood concentrations of estrogen during late pregnancy appear responsible for the elevated levels of prolactin that are necessary to prepare the mammary gland for lactation at the end of gestation. Disease StatesExcessive secretion of prolactin - hyperprolactinemia - is a relatively common disorder in humans. This condition has numerous causes, including prolactin-secreting tumors and therapy with certain drugs. Common manifestations of hyperprolactinemia in women include amenorrhea (lack of menstrural cycles) and galactorrhea (excessive or spontaneous secretion of milk). Men with hyperprolactinemia typically show hypogonadism, with decreased sex drive, decreased sperm production and impotence. Such men also often show breast enlargement (gynecomastia), but very rarely produce milk. Updated 2018. Send comments to |