Prolactin: What It Is, How It Is Produced, And Functions Of This Hormone
The endocrine system produces small molecules called hormones. Hormones act as messengers and influence a multitude of 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 more than 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, by allowing 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: lactation, estrogen treatment and ovulation stimulate the production of prolactin. Other tissues in the human body can also produce it, but in less significant quantities.
In this article we will talk about prolactin detailing all its functions and the problems that can occur if high levels of this hormone occur in the blood.
Prolactin (PRL), also known as lactotropin, is a hormone produced by the pituitary gland which stimulates milk production in the mammary glands and the synthesis of progesterone in the corpus luteum.
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, which weighs approximately 22,500 daltons and its chain consists of about 199 amino acids. The hormone acts in an endocrine, autocrine and paracrine way within the body and influences different systems.
The hormone is produced by different vertebrates and has different functions depending on the species ; As we know, prolactin stimulates milk production in mammals, but for example in the case of fish it is responsible for controlling the balance of salt and water in the body. There are different variants and forms of the hormone by species, in humans there are three small forms of prolactin and several large variants.
Prolactin has a multitude of 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-death factor, also participates in the growth of blood vessels, hematopoiesis and helps blood clotting. In males it relaxes the body after reaching orgasm.
How is prolactin produced?
The pituitary gland, a small gland located at the base of the brain is responsible for producing 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 a 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 (breast milk-producing cells), 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 capable of producing prolactin, the central nervous system, the immune system, the uterus and the mammary glands secrete the hormone in smaller quantities.
There are a series 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 male and female people. Furthermore, in other vertebrate species it participates in other essential tasks of the organism.
Prolactin in females
The hormones progesterone, estrogen and prolactin promote the growth of breast tissue and milk production in pregnant people
Prolactin causes the growth of a particular type of breast tissue called breast alveoli, which are part of the mammary gland. It also causes mammary alveolar cells to produce milk ingredients, increases the production of lactose, casein and other milk-producing proteins in the mammary gland cells, and lipids.
Although elevated prolactin levels are present before the baby is born, milk production does not occur until after delivery. Pregnant people produce high amounts of estrogen and progesterone which, among many other functions, inhibit milk production during pregnancy.
After giving birth, the mother’s progesterone levels drop, causing the mammary alveolar cells to increase the number of prolactin receptors This allows milk to be pumped through the nipples, allowing for breastfeeding.
Prolactin levels can rise or fall after birth, sucking the nipples increases the level of prolactin, breastfeeding stimulates the production of prolactin. If breastfeeding is stopped, 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, making this not happen. Prolactin prevents the production of gonadotropins, a group of hormones involved in regulating reproduction and the cycle.
Prolactin in males
Men also produce prolactin and values ​​considered normal are in the range of 10 to 15 ng/ml. At these levels, prolactin affects kidney function and regulates the amount of electrolytes in body fluids. Some high levels can cause breast development and galactorrhea (milk production), decreased libido and impotence
Also, prolactin would be one of the main causes of some effects of the refractory period. The refractory period is the relaxation time that occurs after ejaculation has occurred and the 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 around it. As in humans, prolactin also influences sexual maturation, reproductive cycles, care of offspring, and breeding in fish. Prolactin doesn’t just affect fish, some studies indicate that elevated levels can cause chickens to display more maternal behavior.
Research with mammals has shown that prolactin levels can affect hair growth This would also occur in birds, where prolactin would have an effect on when they begin to shed their feathers.
Pathologies associated with prolactin
Hormones have to have stable levels. Insufficient or excessive levels can cause various health problems. In the case of prolactin, an amount in the blood above normal can cause certain alterations, such as irregular periods, infertility and erectile dysfunction, among other symptoms But… What can cause these high levels of prolactin?
Certain situations, other than pregnancy and breastfeeding, can cause prolactin levels to rise slightly: e.g. certain medications to treat hyperprolactinemia, stress, epilepsy, breast stimulation, sexual relations, etc. They are factors that can increase the secretion of prolactin in different tissues. Normally, these changes in the amount of prolactin in the blood are usually mild and temporary and do not present relevant symptoms.
If prolactin levels are much higher than normal, in many cases it usually indicates that a prolactinoma, a type of tumor of the pituitary gland A prolactinoma is usually a benign tumor, but if left untreated, the tumor can damage the tissues around it.
The exact origin of prolactinomas is not known, but in some cases they may be related to genetics. Some neoplasms can potentially increase the chance 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.
Some medications that intervene in the production of dopamine, a prolactin inhibitor, can alter hormone levels and produce different symptoms in both men and women.
