Prolactin: role, dosage, properties, breastfeeding

What is the definition of the hormone prolactin?

Prolactin is a natural hormone, that is to say a chemical substance produced by the body, which exerts a specific action on the functioning of one or more organs. 

Prolactin is a hormone secreted by the anterior part of the pituitary gland, a gland located at the base of the brain.

The main and most well-known role of prolactin is to trigger and maintain the lactation process after childbirth. But prolactin is also involved in reproduction, growth, behavior, or even immunity.

Prolactin has an effect mammotrope, that is, it leads to the growth of mammary glands, an effect lactogène, that is to say that stimulates the production of milk, and a on libido and sexual desire. It is said to participate in libidinal balance with other sex hormones (estrogen, progesterone, testosterone).

Prolactinemia: why take a blood test?

Certain pathologies and conditions can cause the level of prolactin in the blood to vary abnormally, which can have consequences, in particular on reproduction or lactation. 

Le determination of prolactin in the blood (or prolactinemia) is indicated when there is a suspicion of hyperprolactinémie, that is to say a prolactin level that is too high, or conversely hypoprolactinemia, when the level is too low (more rare).

For example, a dosage of prolactin is indicated in the event of a problem related to the reproductive system (absence of periods or amenorrhea, infertility, erectile disorders, drop in libido, irregular menstrual cycle, anovulation, etc.).

When the breasts produce milk after a pregnancy or childbirth (we speak of galactorrhea) or en the absence of rise of milk, a determination of prolactin is also indicated. In humans, a gynecomastia, or breast development, may also be an indication.

It should be noted that there are benign tumors of the pituitary gland, in particular prolactin adenoma, which may require an assay for prolactinemia to monitor its evolution (see below).

The determination of prolactin in the blood may or may not be associated with that of other pituitary hormones.

Why do you have to be at rest before taking a prolactin test?

Stress and physical activity may interfere with the results of the blood test, inducing an increase in prolactin. That is why it is advisable to be at rest about ten minutes before the blood sample. 

Note also that the prolactin level fluctuates during the same day, with a peak during the night and another after the meal.

The sample is then taken with an empty stomach, usually in the crease of the elbow.

On what day of the cycle to perform the dosage?

Although it is possible to measure prolactin at any time during the cycle, it is generally advised totake the blood test at the start of the cycle, that is to say before ovulation, during the follicular phase (from D1 first day of menstruation to D14 for a 28-day cycle).

In all cases, the laboratory generally asks for the date of the last period or the number of weeks of amenorrhea in the event of pregnancy. As some medications can also affect your results, it may be helpful to report all your treatments in the laboratory for a better interpretation of the results.

What is the normal level of prolactin?

Prolactin levels are considered to be normal when they are between 5 to 15 ng / mL in men, and between 5 and 20 ng / mL in women.

Note that the reference values ​​are sometimes expressed and mUI / L60 to 450 mIU / L is then equivalent to 5 to 15 ng / mL. Depending on the reagents used, the value of 1 ng / mL corresponds to 22 to 36 mIU / L. The “pathological” threshold is set at 900 mIU / L, ie above 41 ng / mL.

At the end of pregnancy, the prolactin level can reach 250 ng / mL (or ug / L). And when breastfeeding, the rate can vary from 40 to 300 µg / L (or ng / mL), with peaks during feedings (from the time of breastfeeding, to peak at the highest 40 minutes after feeding).

Hyperprolactinemia: when prolactin is too high

We generally speak of hyperprolactinemia when the level of prolactin exceeds 15 ng / mL in men and 20 to 25 ng / mL in women, confirmed by several assays.

What are the causes and symptoms of hyperprolactinemia?

In women, hyperprolactinemia is manifested by menstrual cycle disorders, with in particular a amenorrhea and difficulties or even an absence of ovulation causing infertility. It can also cause secretion of milk (galactorrhea), on one or both breasts, spontaneously, or only with stimulation of the nipple.

In humans, hyperprolactinemia can cause erectile dysfunction as well as a decrease in libido, and also a galactorrhée. More rarely, it can manifest itself by gynecomastia, in other words an excessive development of the mammary gland.

There are several possible causes of hyperprolactinemia, one of which is pituitary gland tumor, benign or not, another disease of the pituitary gland, the taking of certain drugs (antidepressants, morphine, neuroleptics, anti-emetic, etc.), a metabolic disorder (hypothyroidism or renal failure).

Pituitary adenoma: the benefit of the prolactin assay

A pituitary adenoma is a benign tumor located in the pituitary gland. It is also called prolactinoma or prolactin adenoma when this tumor causes too much secretion of prolactin, or hyperprolactinemia.

A pituitary adenoma may be discovered due to symptoms of hyperprolactinemia (galactorrhea, menstrual disorders, erectile disorders, etc.) or due to headache or blurred vision due to compression of brain structures near the pituitary gland.

Regular determinations of prolactin make it possible to observe the evolution of the pituitary adenoma, in particular when drug treatment is undertaken as a first resort, before opting for possible surgery.

The role of prolactin during pregnancy and lactation

Along with other hormones, prolactin is necessary for the proper development of breast cells responsible for milk production, during the first pregnancy. Prolactin also stimulates the synthesis of lipids, carbohydrates and proteins in milk, and lactose. During lactation, she promotes the maintenance of secretory cells and the stability of the junctions between breast cells. Sucking the baby while breastfeeding stimulates the secretion of prolactin.

According to the Leche League France, the level of prolactin increases from 10 weeks of pregnancy, to peak around 150 to 250 µg / L during the 3rd trimester of pregnancy. From the first two days after childbirth, the prolactin level gradually drops over several months. However, peaks of secretion occur during breastfeeding, during and after each feeding. In detail, the level of prolactin increases within minutes of breastfeeding, reaching a maximum approximately 40 minutes after breastfeeding. This sucking response decreases over the months of breastfeeding. It is estimated that when the milk secretion is well launched, the amount of milk produced is not related to the level of prolactin.

Note that physiological hyperprolactinemia that occurs after childbirth contributes to the absence of ovulation in the early postpartum period. This supports the argument of a “contraceptive effect” linked to exclusive breastfeeding.

Prolactin too low: causes and symptoms

Rare, hypoprolactinemia, or abnormal decrease in the level of prolactin, can notably be encountered in the event of hypopituitarism, that is to say a deficiency in one or more pituitary hormones. It can also result from excessive secretion of factors that inhibit prolactin production, cerebral inflammation (meningitis, encephalitis, etc.), cranial trauma or brain tumors. Certain drugs can also be responsible for this phenomenon.