Index
It is a hormone produced by the pancreas and is involved in digestion.
Pancreatic polypeptide is secreted along with insulin, the growth hormone from glucose produced by the pancreas.
The pancreas rapidly releases pancreatic polypeptide after a meal, and its levels remain elevated for 4 to 6 hours. Its secretion is stimulated more strongly by eating protein and fat.
Production of pancreatic polypeptide
Pancreatic polypeptide is secreted by the pancreas along with enzymes and hormones involved in digestion .
Hormones are produced in regions of the pancreas called islets of Langerhans. These islets contain five different types of cells (alpha, beta, delta, epsilon, and PP or gamma), each of which produces a different hormone involved in blood sugar levels .
PP cells produce pancreatic polypeptide.
Hormones produced by the pancreas are released into the bloodstream, where they circulate and affect your target organs.
Function
The pancreatic polypeptide targets many organs. First, it works in the brain through the vagus nerve, which connects the brain to the lungs, heart, and digestive system. This sends information about hunger and satiety to the brain.
Pancreatic polypeptide causes satiety in several ways. In the brain, it reduces appetite. In the digestive system, it slows the rate at which food moves through the digestive system. This makes the feeling of fullness last longer.
This polypeptide also affects various organs in the digestive system. The pancreatic polypeptide relaxes the gallbladder. This stops the release of bile from the gallbladder and slows down digestion.
It also reduces the secretion of other substances, such as digestive enzymes and pancreatic bicarbonate, by the pancreas.
Finally, the polypeptide controls the rate at which food moves through the digestive system.
The pancreatic polypeptide sends signals through different receptors, including Y1, Y2, Y4, and Y5. The Y1 and Y5 receptors stimulate appetite, while the Y2 and Y4 receptors suppress it.
Motilin and pancreatic polypeptide
Motilin is a peptide produced in the small intestine. Like pancreatic polypeptide, motilin is a hormone that controls the digestive system.
Motilin is the opposite of pancreatic polypeptide in several ways. First, its levels decrease after eating, while pancreatic polypeptide is released after eating.
Pancreatic polypeptide causes the gallbladder to relax; motilin causes the gallbladder, stomach, and intestine to contract.
Motilin directly affects the pancreatic polypeptide. In dogs, it stimulates the release of pancreatic polypeptide. Pancreatic polypeptide does not affect motilin release.
The brain-gut axis
Pancreatic polypeptide is one of the hormones involved in the brain-intestine axis. Other hormones include insulin, histamine, and cholecystokinin.
These hormones act on the organs of the digestive system, but they do not do so directly. On the gut-brain axis, hormones produced in the digestive system use nerves and the brain to send signals to the digestive system.
Many of the hormones in the gut-brain axis have opposite effects.
For example, a hormone called leptin causes a feeling of fullness, while insulin stimulates the release of a hormone that causes hunger.
The levels of pancreatic polypeptide and other hormones are controlled by a system of feedback loops, or controls that ensure that food is consumed at the right time and digestion is carried out at the correct rate.
Benefits of high levels of pancreatic polypeptide
Pancreatic polypeptide prevents obesity
One benefit of having high levels of pancreatic polypeptide is the tendency to maintain a lower body weight.
Hormones in the blood control appetite and food intake. These hormones either work long-term by regulating body weight over weeks or months or short-term by affecting appetite within a day.
Pancreatic polypeptide works in the short term. Although this means that the polypeptide only directly affects appetite over the course of a day, eating many days of food combined can cause long-term effects.
When pancreatic polypeptide was injected directly into the stomachs of mice, their food intake decreased and they used more energy. This prevented obesity.
Similarly, mice that produced excess pancreatic polypeptide consumed less food and had less body weight.
Diseases associated with high levels of pancreatic polypeptide
High levels of PP can cause anorexia
People with anorexia experience increased feelings of fullness and reduced hunger. This is caused by abnormal hormone signaling (transmission). In anorexia, food takes longer to pass through the digestive system.
This increased digestion time is a result of transmission of the pancreatic polypeptide. Causes a greater sense of fullness.
In a study of 13 anorexic women, they had increased levels of pancreatic polypeptide. This was true whether or not the people with anorexia were lean, meaning it was not simply a result of weight loss or malnutrition.
The abnormally high levels of pancreatic polypeptide did not decrease after the anorexic patients began eating normally again. This could be a cause of the high relapse rates in people with anorexia.
High levels of PP are associated with acute pancreatitis
Acute pancreatitis is an inflammatory disease of the pancreas. In acute pancreatitis, the pancreas’ own digestive enzymes destroy parts of the pancreas ( self-digestion ).
Early diagnosis is important so that the disease can be treated before complications occur.
To quickly diagnose this disease, there must be a marker that:
- Change soon after pancreatitis starts.
- Stay changed as the disease progresses.
Pancreatic polypeptide can be a good marker for the diagnosis of acute pancreatitis. In animals, blood levels of pancreatic polypeptide rise rapidly after disease begins and remain elevated.
However, there is some debate as to whether this is true in humans.
Furthermore, it appears that pancreatic polypeptide could be useful in the treatment of acute pancreatitis. Hormone secretion outside the pancreatic duct significantly worsens pancreatitis, and pancreatic polypeptide reduces this secretion.
High levels of PP are associated with neuroendocrine tumors
Pancreatic neuroendocrine tumors are cancerous tumors that affect the cells of the pancreas that produce hormones. These tumors can be of two types: functional and non-functional.
Functional tumors have symptoms that are caused by abnormal hormone secretion. Non-functioning tumors may also have abnormal levels of hormones, but the hormones do not cause symptoms.
Different tumors have different hormonal abnormalities. Pancreatic polypeptide is one of the biomarkers used to differentiate the different pancreatic tumors.
High levels of pancreatic polypeptide are seen in various neuroendocrine tumors, such as carcinoid tumors and pancreatic polypeptides. Carcinoid tumors are a group of neuroendocrine cell tumors that can appear in various organs, especially the lungs and digestive tract.
Meanwhile, pancreatic polypeptides are tumors that produce large amounts of pancreatic polypeptide but have few other symptoms.
One review determined that pancreatic polypeptide can be used to identify a tumor when combined with other tumor markers.
High levels of PP are linked to other cancers
Other pancreatic tumors that are not involved with the hormonal system are also associated with elevated levels of pancreatic polypeptide, as are bile duct tumors.
Tumors outside the digestive system also show differences in pancreatic polypeptide levels. For example, patients with other advanced cancers, such as lung cancer, have elevated levels of pancreatic polypeptide.
The pancreas may secrete more pancreatic polypeptide in response to cancer. However, it is also possible that the tumors themselves produce the pancreatic polypeptide.
The presence of pancreatic polypeptide in different tumors means that the polypeptide could be used as a new marker for the diagnosis of tumors. This would increase the speed and accuracy in diagnosing cancer.
Studying pancreatic polypeptide could even lead to new cancer treatments.
High levels of PP are linked to arthritis
Arthritis is inflammation of the joints and causes pain, swelling, and other symptoms. Rheumatoid arthritis is also associated with higher death rates and heart problems.
Pancreatic polypeptide levels are elevated in 54% of people with rheumatoid arthritis, as well as in people with similar diseases, such as scleroderma, mixed connective tissue disease, and temporal arteritis. The magnitude of the increase corresponds to the severity of the inflammation.
Not only does the amount of pancreatic polypeptide increase in people with rheumatoid arthritis, it also increases in people who are at risk for the disease.
Hormones like pancreatic polypeptide may be linked to heart problems experienced by people with rheumatoid arthritis. Pancreatic polypeptide levels are elevated in people with heart disease.
However, not all similar diseases are related to the pancreatic polypeptide. Systemic sclerosis, a connective tissue disease like arthritis, did not cause a change in pancreatic polypeptide levels in fifteen patients.
High levels of pancreatic polypeptide are linked to watery diarrhea syndrome
People with watery diarrhea syndrome may also have hypokalemia (low potassium in the blood), hyperglycemia (high blood sugar), hypercalcemia (high calcium in the blood), and low blood pressure.
Watery diarrhea syndrome itself is a symptom of hormone-secreting tumors.
A case study described a patient with watery diarrhea syndrome and a pancreatic tumor that produced pancreatic polypeptide, insulin, and other hormones.
Another case study involved a person who did not have a pancreatic tumor but had many more pancreatic polypeptide-producing cells than normal.
In an additional study of four people with pancreatic tumors and watery diarrhea syndrome, three of the patients’ tumors had cells that produced the pancreatic polypeptide.
However, in rats, pancreatic polypeptide does not have an effect on the amount of water or electrolytes that are absorbed from the intestines. This suggests that the levels of pancreatic polypeptide do not cause the watery diarrhea syndrome.
Benefits of low levels of pancreatic polypeptide
Having low levels of pancreatic polypeptide in the blood means that a person probably does not have acute pancreatitis or one of several types of hormonal tumors.
Since the secretion of pancreatic polypeptide reduces hunger, having low levels of this polypeptide means that a person is less likely to be malnourished or have symptoms of anorexia.
Diseases related to low levels of pancreatic polypeptide
Low PP levels are linked to chronic pancreatitis and diabetes
Chronic pancreatitis is a long-term inflammation of the pancreas. It does not heal over time and can get worse and lead to complications, such as pancreatogenic diabetes and glucose intolerance.
Diabetes in pancreatitis occurs because inflammation destroys the cells that make insulin. In pancreatogenic diabetes, the cells that make pancreatic polypeptide and other hormones are also destroyed.
It is important to be able to distinguish pancreatogenic diabetes from type 1 or type 2, as the treatment is different.
This is done by testing pancreatic polypeptide levels: low pancreatic polypeptide levels means pancreatogenic diabetes.
Low levels of PP and obesity
Prader-Willi syndrome is a complex disorder that causes, among other symptoms, an insatiable appetite. People with this disorder tend to be obese, and many die from complications of obesity.
People with Prader-Willi syndrome release less pancreatic polypeptide after eating than people without the disorder. One study showed smaller increases or no increases in pancreatic polypeptide levels after eating in six of the seven people with Prader-Willi syndrome.
Failure to experience fullness is caused by a deficiency in pancreatic polypeptide release.
Furthermore, even obese people without this disorder have a reduced pancreatic polypeptide response after eating.
In contrast, peripheral administration (injection into veins) of pancreatic polypeptide to 16 obesity-prone individuals suppresses the tendency to gain excess weight by reducing food consumption by 12% in human patients.
Pancreatic Polypeptide and bone density
The body always builds bones and then breaks them down again. It is important to maintain a balance between this production and the destruction of bone tissue. If more bone is destroyed than is created, the bones will be brittle and break easily.
Cells that form bone are called osteoblasts, while cells that reabsorb bone are called osteoclasts. Both cells are controlled by hormones, and pancreatic polypeptide is one of those hormones.
Pancreatic polypeptide affects the creation of bone-producing cells, which in turn could increase the number of these cells.
Some studies suggest that preventing the pancreatic polypeptide from functioning reduces the number of bone-producing cells. However, this has been contradicted in other studies.
Increased pancreatic polypeptide
One way to increase pancreatic polypeptide release is to exercise. Exercise results in an energy deficit, which in turn stimulates the release of the pancreatic polypeptide. In thirteen obese people, pancreatic polypeptide levels increased by 38% after 15 days of exercise.
Histamine injection temporarily increases pancreatic polypeptide levels by 86% in humans.
Histamine is a chemical that is released by the body in response to injury or inflammation.
However, excess histamine can cause symptoms similar to an allergic reaction. Congestion, headache, and elevated heart rate can be caused by too much histamine.
Increased pancreatic polypeptide with cholecystokinin
Cholecystokinin is a hormone produced in the intestine. It causes the gallbladder to contract and stimulates secretion from the pancreas. Like pancreatic polypeptide, cholecystokinin increases fullness and reduces food intake.
Some research has shown that cholecystokinin causes the release of pancreatic polypeptide. In 6 healthy volunteers, after cholecystokinin infusion, blood pancreatic polypeptide levels were significantly higher than normal.
Levels returned to normal 45 minutes after infusion.
However, another study involving eighteen healthy people showed no changes in pancreatic polypeptide levels after injecting cholecystokinin into the blood.
Decrease pancreatic polypeptide
Some people, such as those with anorexia, may benefit from a reduction in pancreatic polypeptide levels.
One way to lower the amount of pancreatic polypeptide in the blood is with atropine.
Atropine is a drug naturally produced by the belladonna plant.
In humans, atropine blocks the release of the pancreatic polypeptide while reversing the effects that the pancreatic polypeptide has on the digestive system.
However, atropine can cause side effects including altered mental status, elevated heart rate, and the inability to sweat.
Pancreatic polypeptide tests
Pancreatic polypeptide blood test
The pancreatic polypeptide test measures the levels of pancreatic polypeptide in the blood. The level is high if the patient has a pancreatic tumor, diabetes, duodenal ulcer, or has recently eaten.
This test is used primarily in the diagnosis of pancreatic tumors. Because of this, it is mostly done in people who have yellowish (jaundiced) skin, weight loss, or stomach pain, as these are symptoms of pancreatic tumors.
Vagal nerve function test
Some stomach surgeries run the risk of damaging the vagus nerve, which carries information between the brain and the heart, lungs, and digestive system.
Damage to the vagus nerve can cause swelling, pain, and other symptoms, so it’s important to be able to test its function.
Traditionally, vagus nerve damage has been proven by stimulating the activity of the nerve or by injecting insulin into the patient, but the former method is invasive and the latter can lead to dangerous complications.
A safer and easier way to test for vagus nerve problems is to measure pancreatic polypeptide levels. After chewing food, the amount of pancreatic polypeptide in the blood should increase.
If the level does not rise, or only rises slightly, then the vagus nerve has been damaged.
