Motilin - An Overview

Introduction

Gastrointestinal hormones play an important part in the proper functioning of the gastrointestinal tract. Hormones are peptides released into the portal system, which targets specific body cells. Motilin is a 22 amino acid oligopeptide released by the Mo cells or the enteroendocrine cells and is mainly present in the mucosal epithelium of the duodenum. They are released cyclically after eating, drinking water, and fasting. Bile acids and duodenal acidification control the cyclic release of motilin, mainly during the fasting state.

What Is Motilin?

Motilin is a hormone produced by the intestinal cells of the gastrointestinal tract. The body releases the hormone to help move the food from the small intestine to the large intestine. This food movement is called the migrating motor complex (MMC). The main function of the motilin hormone is to facilitate movements and empty the stomach by stimulating muscle contractions. The body releases the motilin hormone throughout the day. Motilin hormone production also increases during sleep, fasting, or between meals when a person is not eating. Its level also varies on the food that a person eats. For example, motilin levels are seen as low with fatty or sugary foods.

What Are the Phases of Migrating Motor Complex (MMC)?

Migrating motor complex begins from the upper gut region and is characterized by four phases.

• Phase I is when the smooth muscles are inactive.

• Phase II increases the digestive tract's peristaltic activity (sequence of muscle contractions).

• Phase III is the characteristic phase of MMC and has the most contractions. In the third phase, the pylorus remains open, allowing undigested food into the small intestine.

• In phase IV, a decrease in activity and its return to the baseline occurs.

The vagus nerve, part of the parasympathetic nervous system, controls the migrating mortal complex in the stomach. The vagus nerve does not control motilin levels; however, it regulates other digestive hormones like pancreatic enzymes and gastrin.

Where Are the Receptors of Motilin Located?

The motilin receptors are G protein couple receptors located along the digestive tract (the stomach, small intestine, and colon). Motilin receptors are more concentrated in the pyloric antrum, a narrow part of the stomach. The pyloric antrum is the beginning portion of the pylorus which is the opening between the stomach and the small intestine. The activation of motilin receptors leads to the contraction of smooth muscles.

What Are the Functions of Motilin?

• The primary function of the motilin hormone is to move food through the gastrointestinal tract.

• When the motilin hormone is released from the body, it gets bound to cells called the motilin receptors. This binding causes the muscles in the small intestine to contract.

• Motilin also stimulates the motility of the stomach and small intestine; these muscle contractions help in the movement of food to the large intestine.

• It stimulates the release of other hormones like somatostatin and pancreatic polypeptide and helps produce a stomach enzyme called pepsin. Pepsin is a stomach enzyme that helps in the digestion process by helping the body digest protein.

• Motilin increases the actions of the neurotransmitter acetylcholine. This neurotransmitter is responsible for the contraction of intestinal muscles in the gut.

• Motilin also regulates the migrating motor complex.

• The migrating motor complex ensures that neither the bacteria nor any leftover food will block the absorption of the nutrients. MMC also performs various functions like transporting the digested food from the small intestine to the large intestine, moving the bacteria present in the small intestine to the large intestine to prevent an overgrowth of bacteria, and preventing the bacteria from traveling backward from the large intestine towards the end portion of the small intestine.

• The motilin hormone also helps empty the gallbladder, release insulin from the pancreas, and trigger hunger signs.

• Together the motilin hormone and the ghrelin hormone stimulate gastric emptying. Gastric emptying is a process of food movement from the stomach to the duodenum (the first part of the small intestine).

Which Conditions Affect the Motilin Levels?

Certain conditions cause variations in motilin levels. They are:

1. Low Motilin Levels - Low levels of motilin in the body are also known as hypomotility; it can cause decreased contractions of muscles and movements in the digestive tract. Conditions associated with hypo-motility include:

• Gastroparesis occurs when the movement of the stomach muscles reduces, or it stops working, thus preventing the stomach from emptying its contents.

• Irritable bowel syndrome is a condition of the digestive system associated with symptoms like abdominal pain, bloating, and diarrhea.

• Intestinal pseudo-obstruction is a rare condition characterized by intestinal obstruction.

• Chronic constipation

• Functional dyspepsia is a type of chronic indigestion.

Low levels of motilin are also noted during pregnancy. Low levels cause heartburn and constipation in pregnant women.

2. High Motilin Levels - High levels of motilin in the body are called hypermotility and they can cause increased intestinal contractions and faster food movements. Conditions that cause hypermotility include ulcerative colitis and diabetes. Ulcerative colitis is a condition characterized by inflammation and the formation of ulcers in the digestive tract.

How to Maintain Motilin Levels and Keep the Digestive System Healthy?

The digestive system and hormones can be kept healthy by adopting healthy lifestyle habits. Some of the habits include:

• At least seven to eight hours of sleep is required every night.

• Drink about three to four liters of water daily; the quantity can vary depending on the size, gender, and physical activity a person performs.

• Ensure to include fruits, vegetables, and whole grains in the diet.

• Try exercising daily.

• Avoid drinking alcohol, excessive caffeine intake, smoking, and processed foods.

• Avoid the overuse of antibiotics and take them only when needed.

Conclusion

Motilin is a gastrointestinal hormone produced by the intestines. It facilitates movements and emptying of the digestive system by stimulating muscle contractions of the intestine. These hormones are mainly produced after meals and while fasting. Low levels of motilin are noted in conditions like chronic constipation, chronic indigestion, and irritable bowel syndrome; high levels of motilin are noted in conditions like diabetes and ulcerative colitis. An appropriate level of motilin is essential for the proper functioning of the digestive tract. Adequate lifestyle modifications like drinking enough water, avoiding smoking and drinking, sleeping well, and exercising regularly can help maintain the motilin level and keep the digestive system healthy.