Prolactin

Prolactin is a hormone produced in the pituitary gland of humans, other mammals, and some other species. It is primarily responsible for readying the body to produce milk. However, it is linked to a number of other functions and is present in both females and males. The level of prolactin in the body can both cause health conditions and be an indicator of a health problem, particularly those related to fertility issues. It has also been found that men who are fathers have a higher level of prolactin than those who have not fathered a child.

Background

The pituitary gland is a small organ located near the base of the brain that is responsible for regulating how the body grows, how the body uses energy (metabolism), and the sexual development of the body. When a female is pregnant or has just given birth, the pituitary gland releases the hormone prolactin. The name means "prior to lactation" or "promoting lactation," which is the process of producing milk. The hormone's main function is to prepare the female to provide milk for her offspring.

The hormone is present in both females and males. However, unless the female is pregnant or nursing, the amount of prolactin produced is usually very small. Pregnancy stimulates the pituitary gland to produce more prolactin to prepare for nursing. Once the baby is born, the act of nursing stimulates the pituitary to produce more prolactin, which in turn stimulates the breasts to produce more milk. This helps regulate the supply so that the baby receives the amount of nourishment needed. As other food sources are introduced and nursing decreases, the amount of prolactin also decreases. When nursing ceases, prolactin levels decrease significantly.

Since the pituitary gland regulates other sexual functions, the production of prolactin serves as a signal to the gland to not trigger the production of some of the other hormones that regulate reproductive functions. For this reason, the menstrual cycle of a nursing mother is usually interrupted and she does not experience a monthly period until nursing begins to taper down. However, this is not a foolproof process, and it is still possible for the reproductive cycle to remain or become active; in this case, pregnancy can result even while the mother is nursing.

Overview

While its main function is to regulate the production of breastmilk, prolactin appears to play several roles in the reproductive systems of both men and women. Higher levels of prolactin during nursing curtails the woman's reproductive function and lessens the likelihood of pregnancy. This can serve as a natural way to space children. Its function in men is less clear, although twenty-first century research has indicated that men who have fathered a child produce more prolactin and less testosterone. This phenomenon has been observed not only in human fathers but in male wolves, meerkats, marmosets, emperor penguins, and pipefish, where an increase in prolactin triggers the development of a pouch the male fish uses to incubate his mate's eggs. How this works is not well understood. However, some studies have shown that interaction with his offspring affects the amount of prolactin produced by the male.

Outside of childbirth and childcare situations, the presence of higher levels of prolactin can be an indicator of a problem. The most common cause of high prolactin levels is a tumor on the pituitary gland. This usually non-cancerous growth is called a prolactinoma. It can occur in both men and women and can cause headaches and vision problems. Other symptoms in women include the production of breastmilk when not pregnant or nursing, pain during sex, increased acne, and increased facial and body hair. In men, it can cause reduced sex drive and fertility issues and a reduction in facial and body hair. In either sex, it can cause swollen breasts and the release of a milky discharge, a condition known as galactorrhea.

If a prolactinoma is suspected, the physician will order a simple blood test to measure the level of prolactin in the blood. Normal prolactin levels are 2 to 18 nanograms per milliliter for males, 2 to 29 nanograms per milliliter in non-pregnant females, and 10 to 209 nanograms per milliliter in pregnant or nursing females. If the test levels are above this, imaging tests such as magnetic resonance imaging (MRI) or computerized axial tomography (CAT) scans will be ordered to continue the diagnostic process.

A number of other conditions besides prolactinomas can also cause high prolactin levels, known as hyperprolactinemia. These include diseases of the thyroid or thalamus glands, kidney disease, other types of pituitary tumors besides prolactinoma, and injury or irritation to the chest wall that confuse the body into thinking nursing is going on. A number of different medications can also trigger higher levels of prolactin, including some antidepressants and sedatives, estrogens, oral contraceptives, some antinausea medications, some stomach acid reducers, and some blood pressure medications.

In some cases, a blood test may show a high prolactin level that goes away on its own. This is because stress, high-protein meals, certain kinds of breast stimulation, and very recent exercise can temporarily elevate prolactin levels. This type of high level is not serious.

High prolactin levels from any of these causes can alter the reproductive cycle in women and cause infertility issues, or difficulty getting pregnant. Hyperprolactinemia interferes with ovulation, or the production of eggs, and so can prevent a woman from becoming pregnant. This interference can be ongoing or can happen intermittently. High prolactin levels can also interfere with the release of another hormone, progesterone, after ovulation occurs. Progesterone is responsible for preparing the uterus for the implantation of the egg; if progesterone levels are too low, the woman may conceive but the fertilized egg will not be able to fasten itself to the uterine lining and pregnancy will not result.

High prolactin levels can be corrected by addressing the cause. This can mean surgery to remove a tumor, treatment of another health condition such as a thyroid or thalamus problem, or a change of medication that is triggering the problem.

Bibliography

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Gholipour, Bahar. "Men's Sexual Problems Linked to Low Prolactin Levels." LiveScience, 19 Nov. 2013, www.livescience.com/41322-low-prolactin-men-sexual-impairment.html. Accessed 17 Mar. 2017.

Gray, Peter B. "Prolactin Is for Men, Too." Psychology Today, 3 July 2012, www.psychologytoday.com/blog/the-evolving-father/201207/prolactin-is-men-too. Accessed 17 Mar. 2017.

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