The endocrine system produces small molecules called hormones. Hormones act as messengers and influence many important processes in the body: they help maintain blood pressure, regulate sexual desire, and control hunger, among other essential tasks. The same hormone can have different functions.
Prolactin is a protein hormone responsible for over 300 different processes in vertebrates, including humans. It is best known for its role in breast growth and milk production during pregnancy and after childbirth. In addition, to allow breastfeeding, it helps regulate the immune system, intervenes in the regulation of our metabolism and allows the development of the pancreas.
This hormone is secreted by the pituitary gland in response to different events: breastfeeding, estrogen treatment and ovulation stimulate the production of prolactin. Other tissues of the human body can also produce it, but in less quantity.
In this article we will talk about prolactindetailing all its functions and the problems that can arise with high levels of this hormone in the blood.
What is prolactin?
Prolactin (PRL), also known as lactotropin, is a hormone produced by the pituitary gland which stimulates the production of milk in the mammary glands and the synthesis of progesterone in the yellow body.
Prolactin is a peptide hormone, encoded by the PRL gene. In 1970, Henry Friesen confirmed its existence in humans; however, the hormone had already been discovered in other animals in 1930. It is a polypeptide that weighs about 22,500 daltons and its chain consists of 199 amino acids. The hormone acts endocrine, autocrine and paracrine in the body and influences different systems.
The hormone is produced by different vertebrates and has different functions in different species; as we know, prolactin stimulates milk production in mammals, but for example in the case of meat, it is responsible for controlling the balance of salt and water in the body. There are different variants and forms of the hormone per species, in humans there are three small forms of prolactin and several large variants.
Prolactin has many functions in the body. In the human species, it not only stimulates breast growth and milk production during pregnancy and after childbirth, it also plays a role in the immune system and has multiple functions related to the cell cycle, acting as a growth factor, differentiator and anti-mortality factor, also participates in the growth of blood vessels, hematopoiesis and helps in blood clotting. Males relax the body after reaching orgasm.
How is prolactin produced?
The hypophysis or pituitary gland, a small gland located at the base of the brainis responsible for the production of prolactin in response to different stimuli such as ovulation.
The hypothalamus contains cells that control the secretion of many hormones, including prolactin. The tuberoinfundibulum is part of the arcuate nucleus of the hypothalamus and contains nerve cells that secrete dopamine, also known as the prolactin inhibiting hormone. These neurons control D2 receptors in lactotrophs (cells that produce breast milk), reducing prolactin secretion. Another group of neurons in the hypothalamus, called thyrotropin-releasing factor neurons, increase prolactin secretion. Although prolactin is the only pituitary hormone whose primary control is inhibitory, it is not the only hormone regulated by these endocrine neurons.
Although most of the prolactin in the body is secreted by the pituitary gland. Other organs and systems of the human body are able to produce prolactin, the central nervous system, the immune system, the uterus and the mammary glands secrete the hormone in smaller quantities.
There are a number of factors that can stimulate prolactin production in any of the above tissues, including: nipple stimulation, exercise and stress.
Its functions in the body
Prolactin has a wide variety of functions. However, its effects vary between men and women. Moreover, in other species of vertebrates, it participates in other essential tasks of the organism.
Prolactin in women
The hormones progesterone, estrogen and prolactin they promote breast tissue growth and milk production in pregnant women.
Prolactin causes the growth of a special type of breast tissue called the mammary alveoli, which are part of the mammary gland. It also causes the production of dairy ingredients by the mammary alveolar cells, increases the production of lactose, casein and other milk-producing proteins in the cells of the mammary gland and lipids.
Although high levels of prolactin are present before the baby is born, milk production does not occur until after birth. Pregnant women produce large amounts of estrogen and progesterone which, among many other functions, inhibit milk production during pregnancy.
After childbirth, the mother’s progesterone levels drop, causing the alveolar cells in the breast to swell increase the number of prolactin receptors. This allows milk to be pumped through the nipples, allowing breastfeeding.
Prolactin levels can rise or fall after birth, nipple sucking increases prolactin levels, breastfeeding stimulates prolactin production. If you stop breastfeeding, milk production decreases and prolactin levels return to normal one or two weeks after the child is weaned.
It has been shown that high levels of prolactin can interfere with the menstrual cycle, which does not happen. Prolactin prevents the production of gonadotropins, a group of hormones involved in reproductive and cycle regulation.
Prolactin in men
Men also produce prolactin and the values considered normal are around 10 to 15 ng/ml. At these levels, prolactin affects kidney function and regulates the amount of electrolytes in body fluids. High levels they can cause breast enlargement and galactorrhea (milk production), decreased libido and impotence.
Also, prolactin would be one of the main causes of certain effects of the refractory period. The refractory period is the time of relaxation that occurs after ejaculation and loss of erection after intercourse, it is characterized by a decrease in sexual appetite and genital hypersensitivity that are accompanied by a state of relaxation and drowsiness, the latter effect would be induced by prolactin.
Functions in other vertebrate species
Prolactin has a multitude of functions in fish, mainly in homeostasis, that is, in the exchange of water and salts between a fish and the sea that surrounds it. As in humans, prolactin also influences parts, sexual maturation, reproductive cycles, care of offspring, and breeding. Prolactin doesn’t just affect chunks, some studies indicate that high levels can cause hens to show more maternal behavior.
Research on mammals has shown that prolactin levels they can affect hair growth. This would also happen in birds, where prolactin would have an effect on when they start changing feathers.
Pathologies associated with prolactin
Hormones must have stable levels. Insufficient or excessive levels can cause different health problems. In the case of prolactin, an amount in the blood greater than normal can cause certain alterations, such as irregular menstruation, infertility and erectile dysfunction, among other symptoms. But… What can cause these high prolactin levels?
Certain situations, apart from pregnancy and breastfeeding, can cause a slight increase in prolactin levels: fear Example, certain medications to treat hyperprolactinemia, stress, epilepsy, breast stimulation, sexual relations, etc. are factors that can increase prolactin secretion in different tissues. Normally, these changes in the amount of prolactin in the blood are usually mild and temporary and do not show relevant symptoms.
If prolactin levels are much higher than normal, in many cases this usually indicates that it has developed a prolactinoma, a type of tumor of the pituitary gland. A prolactinoma is normally a benign tumor, but if left untreated, the tumor can damage surrounding tissue.
The exact origin of prolactinomas is not known, but in some cases they can be linked to genetics. Certain neoplasms can potentially increase the possibility of developing this type of tumor. In terms of prevalence, women are more likely to develop prolactinoma than men, and diagnosis usually occurs between the ages of 25 and 34.
Certain drugs that are involved in the production of dopamine, a prolactin inhibitor, can alter hormone levels and produce different symptoms in men and women.
- Al-Chalabi, M., et al. (2021). Physiology, prolactin.
- Elgellaie, A., et al. (2021). Plasma prolactin is higher in major depressive disorder and in women, and associated with anxiety, hostility, somatization, psychotic symptoms, and heart rate.
- Yatavelli, RK, et al. (2021). Prolactinoma.