Prolactin facts for kids

Kids Encyclopedia Facts

Prolactin is a natural chemical messenger, or peptide hormone, found inside living bodies. Most people know it because it helps mother mammals make milk to feed their babies, which is called lactation. However, this tiny helper does hundreds of other jobs too. Scientists have discovered that prolactin plays a role in more than 300 different bodily actions across many kinds of animals. It is a special kind of protein made by a tiny control center in the brain called the pituitary gland.

Prolactin acts in many ways, including like a cytokine, helping cells talk to one another. It helps balance metabolism, supports the immune system, and aids early organ growth. It also helps control how cells grow and multiply. It can even stop cells from dying off before they are supposed to, an action related to preventing early cell death or apoptotic breakdown. Whether helping an animal grow strong or caring for its young, prolactin is a truly busy hormone.

How Scientists Discovered Prolactin

Early Animal Discoveries

Scientists first uncovered clues about prolactin in animals around the year 1930. An American biologist named Oscar Riddle was studying how animals care for their young. He noticed that a particular substance from the brain caused birds to feed their chicks. He also noticed that it caused mother animals to produce milk. Riddle chose the name prolactin because the hormone promoted lactation.

Finding Prolactin in Humans

For many years, scientists wondered if humans made the exact same chemical. In 1970, a Canadian researcher named Henry Friesen proved that the human body makes its own prolactin. He showed that it is distinct from human growth hormone. The instructions to build this hormone come from a specific code in our DNA called the PRL gene.

What Does Prolactin Do in Humans?

Making Milk for Babies

The most famous job of prolactin is helping new mothers feed their newborns. When a mother becomes pregnant, her mammary gland tissues grow and change. Prolactin levels rise significantly during this time. While baby is still developing, high amounts of other body chemicals like progesterone and estrogen hold prolactin back from making milk right away. Once the baby arrives, those other chemicals drop rapidly. Prolactin then takes over to fill the breast tissues with nourishing milk.

Protecting and Guiding Maternal Behavior

Prolactin does more than just prepare food. It also influences feelings and parental instincts, supporting maternal behavior. When a mother cuddles and feeds her newborn, nerve signals travel along her spinal cord directly up to her brain. These signals prompt the pituitary gland to release steady pulses of prolactin. Prolactin also helps mother animals develop strong protective bonds with their offspring.

Helping the Growing Brain and Nerves

Prolactin protects the nervous system in amazing ways. Inside the central nervous system, long nerve fibers called axons need special protection to carry electrical signals quickly. Prolactin encourages cells called oligodendrocyte precursor cells to divide and flourish. These young cells turn into adult oligodendrocytes. These specialized helpers wrap nerve fibers in a protective fatty blanket called myelin.

Prolactin also helps make brand-new brain cells, a special process known as neurogenesis. It encourages this new cell growth in both the mother's brain and the developing fetal brain. Furthermore, near the end of development before birth, prolactin helps the unborn child's lungs make pulmonary surfactant. This slippery fluid keeps tiny air sacs in the lungs from sticking shut during breathing. Prolactin also teaches the mother's body to welcome the baby through natural immune tolerance.

Regulating Blood and Tissues

Prolactin acts as a versatile building coordinator for the bloodstream. It influences hematopoiesis, which is how the body makes fresh red and white blood cells inside bone marrow. It also helps manage angiogenesis, the creation of new blood vessels when tissues repair themselves. In addition, it helps regulate how blood clots form to seal tiny scrapes and cuts.

Moods and Feelings

Scientists studying music psychology think prolactin may help explain why people sometimes enjoy listening to sad songs. When someone feels sad or moved by gentle music, prolactin levels rise slightly. This small increase can create a comforting, soothing feeling in the brain. Prolactin helps smooth out tense emotions and brings a sense of calm rest after stressful events.

Prolactin in Animals Across the World

Water and Salt Balance in Fish

Mammals are not the only creatures that rely on prolactin. In fish, prolactin performs an entirely different main job called osmoregulation. Osmoregulation is the art of balancing water and salt inside the body. A freshwater fish needs to keep its body from absorbing too much plain water, while a saltwater fish must keep from drying out. Prolactin signals the gills, kidneys, and gut of the fish to keep salt levels perfectly balanced.

Some fish also use prolactin for childcare. In the rivers of South America, parents of the discus fish make a nourishing slime on their skin. Prolactin tells their skin cells to produce this healthy coating, which the tiny young fry eat until they are large enough to hunt on their own.

Amazing Feathers and Crop Milk in Birds

In the bird kingdom, prolactin helps manage how feathers grow and shed during moulting. Prolactin also triggers deep parenting habits in birds. For example, it encourages a mother hen to sit patiently on her nest of eggs for weeks to keep them warm.

Some birds feed their chicks a special fluid called crop milk. Pigeons, bright pink flamingos, and even the hardy male emperor penguin make this nutrient-rich food inside their throats. Prolactin tells the bird's digestive lining to thicken and release this milky food so the newly hatched chicks can grow strong.

Fur Growth in Mammals

Prolactin also tells hair and fur when to grow and when to rest. The hormone works inside hair follicles in mammalian skin. When prolactin levels rise during certain seasons, it can slow down hair growth or trigger shedding. In farm animals like cattle, a genetic mutation in the prolactin system can produce very short, shiny hair known as a "slick" coat. This short fur helps cows stay cool during hot summer days.

How the Body Controls Prolactin

Brain Signals and the Pituitary Gland

The body must keep prolactin levels carefully balanced. Deep in the center of the brain lies the hypothalamus. A small group of nerve cells in the arcuate nucleus uses the tuberoinfundibular path to release a chemical messenger called dopamine. Dopamine connects with the D2 receptor on milk-making cells called lactotrophs in the anterior pituitary. When dopamine docks there, it tells the gland to stop releasing prolactin. Dopamine is the primary brake pedal for prolactin.

When prolactin is needed, dopamine production drops. Other brain chemicals can gently press the gas pedal. One helper is thyrotropin-releasing hormone, which asks the pituitary gland to release prolactin into the bloodstream. Scientists have also looked for a direct prolactin-releasing hormone, testing substances like prolactin-releasing peptides and VIP. During nursing, signals also prompt the release of oxytocin from the posterior pituitary gland, helping milk flow smoothly.

Daily Rhythms and Natural Changes

Prolactin levels do not stay the same throughout the day. Instead, they follow a natural diurnal daily rhythm. Prolactin levels climb while people sleep, especially during dreaming stages, and peak in the early morning hours. Levels can also temporarily jump after hard physical exercise, after eating high-protein meals, or during emotional stress.

How Prolactin Delivers Messages to Cells

Prolactin travels through the bloodstream like a letter carried in an envelope. To deliver its note, it must find a matching prolactin receptor on the surface of a target cell. These receptors are located in the heart, lungs, liver, kidneys, spleen, thymus, adrenal glands, uterus, skeletal muscle, and skin.

When prolactin touches its receptor, two receptors join together, which scientists call forming a dimer. This pairing turns on a helper protein inside the cell called Janus kinase 2. This helper switches on a chemical highway called the JAK-STAT pathway. It also activates helpful cell enzymes like mitogen-activated protein kinases and Src kinase. These internal signals tell the cell's nucleus which proteins to make.

The Shapes and Sizes of Prolactin

The basic prolactin molecule is a folded chain built of 199 amino acids. It keeps its tidy shape using three internal bonds called disulfide bonds. Its shape looks very similar to other messenger proteins, such as human growth hormone and placental lactogen.

Inside the blood, prolactin can appear in several sizes:

Little prolactin: This is the most common form. It has a tiny molecular weight of about 23 kilodaltons (kDa). It does almost all the hormone's daily work.
Big prolactin: This middle-sized form weighs around 48 kDa. It is formed when a few prolactin units stick together, but it does not have much biological activity.
Macroprolactin: This extra-large bundle weighs around 150 kDa. It floats through the bloodstream harmlessly without carrying out normal prolactin tasks.
Other small variants: The body can also break prolactin down into tiny 14, 16, or 22 kDa pieces for special jobs.

Why Doctors Test Prolactin Levels

Checking Hormone Health

Doctors sometimes measure prolactin to see how well the brain's endocrine glands are communicating. If prolactin levels become unusually high, a condition known as hyperprolactinemia occurs. Too much prolactin can block other brain signals like gonadotropin-releasing hormone, follicle-stimulating hormone, and luteinizing hormone. This blockage can disrupt healthy adult reproduction and cause unexpected milk production, called galactorrhoea.

High prolactin levels can be caused by a small, benign lump in the pituitary gland called a prolactinoma. When doctors discover a prolactinoma, they often give medicines that mimic dopamine, like bromocriptine or cabergoline. These medicines tell the pituitary gland to shrink the lump and slow down prolactin release.

Prolactin and Seizures

Doctors also use prolactin tests to learn more about sudden nerve events. During an epileptic seizure, intense bursts of electrical activity spread across the brain. This electrical surge usually causes the pituitary gland to pour extra prolactin into the blood right away. By checking blood prolactin soon after an event, doctors can tell whether a patient experienced an epileptic event or another condition.

Measuring Units in the Laboratory

Scientists measure prolactin in blood samples using several types of laboratory units. They might express concentrations as mass concentration, like nanograms per millilitre (ng/mL) or micrograms per liter (μg/L). They may also use molar concentration units like nanomoles per liter (nmol/L).

To ensure every laboratory gets matching answers, the WHO Expert Committee on Biological Standardization created international reference samples. Laboratories calibrate their tools against these freeze-dried or lyophilized human prolactin samples. This careful system helps doctors worldwide read blood tests accurately.

Summary of Prolactin's Wonder

Prolactin is one of the most versatile hormones in the animal kingdom. From balancing salt inside freshwater fish to protecting bird eggs and helping human mothers nourish their babies, prolactin touches life across the globe. By constantly sending vital signals to the immune system, brain cells, and organs, this tiny protein helps keep living creatures healthy, balanced, and ready to care for future generations.