Cholecystokinin: what it is, and effects of this hormone and neurotransmitter

Cholecystokinin (CCK) is a hormone that is secreted in the intestine. and is activated in response to the ingestion of certain foods. It is involved in processes such as digestion and appetite, generating a feeling of satiety that helps us regulate appetite.

In this article we explain in more detail what this hormone is and what functions it performs, how the effect is produced of satiety and what the latest research says about its possible role in preventing deterioration cognitive.

• Related article: "Types of hormones and their functions in the human body"

What is cholecystokinin?

Cholecystokinin is produced in the small intestine, specifically in the duodenum and jejunum, and causes contraction of the gallbladder and pancreatic secretion. This hormone is also considered as a neurotransmitter that is released in the nervous system., especially in the hypothalamus.

This hormone belongs to the group of kinins, which are formed from globulins (a group of water soluble proteins and present in animals and plants) by the enzymatic action proteolytic. Proteolysis consists of the degradation of proteins, either by specific enzymes or through intracellular degradation.

The secretion or production of cholecystokinin depends on factors such as the presence of some nutrients from food stored in the intestine, mainly fats and proteins (fatty acids and amino acids).

functions

Cholecystokinin fulfills several functions, both in its role as a gastrointestinal hormone and in its role as a neurotransmitter in the nervous system.

As a gastrointestinal hormone

Cholecystokinin, together with gastrin and secretin, constitutes one of the main hormones secreted at the gastrointestinal level. CCK secretion and its effects on gastric motility are known to depend on the fats ingested., specifically the length of the fatty acid chain.

• CCK acts as a satiety signal and once released it has multiple effects on the gastrointestinal system, performing the following functions:
• It causes the contraction of the gallbladder, facilitating the excretion of bile into the duodenum, which is involved in the digestion processes.
• Stimulates the secretion of hydrochloric acid in the stomach, to promote digestion by breaking down food.
• It regulates the pancreatic secretion of enzymes and hormones, such as insulin and glucagon, regulating hepatic and blood glucose production.
• Stimulates relaxation and the opening of the sphincter of Oddi, a muscle that opens in response to food so that bile and pancreatic digestive juices enter the duodenum and mix with food to make the digestion.

as a neurotransmitter

cholecystokinin has also been found in the brain (mainly in the cortex, but also in other areas such as the retina, hippocampus, hypothalamus and spinal cord) and plays a role as a neurotransmitter or neuromodulator, acting on the neurons of the periaqueductual gray matter, which are related to the perception of pain, and on the neurons of the medial hypothalamus, which are in charge of controlling the intake of food.

CCK levels usually rise towards the end of the meal., triggering satiety mechanisms. The presence of CCK in the amygdala and in some areas of the cerebral cortex has led researchers to suggest that this hormone could have a role related to emotions.

It has also been discovered that cholecystokinin has an anxiogenic (anxiety-causing) function in the brain, as various studies have shown that injecting agonists into one of CCK receptors produce autonomic and behavioral changes associated with sensations such as fear and anxiety, while antagonist substances cause all the contrary.

The CCK also seems to interact in synapses with another neurotransmitter, dopamine, especially in the nigrostriatal fibers that innervate the striatum and the nucleus accumbens, a brain structure involved in reward systems and responsible for integrating motivational information with emotions and actions motor.

• You may be interested in: "Types of neurotransmitters: functions and classification"

CCK and the satiety effect

Cholecystokinin (CCK) is the best-studied satiety-inducing peptide. Let's see, next, how this effect is produced.

CCK is secreted by I cells of the mucosa of the duodenum and jejunum in response to the presence of partially digested fats and carbohydrates from the stomach.

This hormone, as we have previously mentioned, causes contraction of the gallbladder, release of pancreatic enzymes, inhibition of motility and gastric emptying, thus decreasing the size of the ingested food.

Cholecystokinin secretion is activated by the presence of products derived from the breakdown of fats, peptides, amino acids and, to a lesser extent, carbohydrates in the diet; and it is inhibited by the intestinal concentration of pancreatic proteases (trypsin and chymotrypsin) and bile, after ingestion of food.

CCK causes contraction of the pylorus (the lower opening of the stomach that communicates with the small intestine), generating a gastric distension that activates the vagal afferents that take over in the nucleus of the solitary tract to, finally, stimulate the center of the satiety; a satiating effect that lasts approximately 90 minutes.

Recent research

Recent research by scientists at the University of Iowa in the United States suggests that a high level of cholecystokinin could decrease a person's chance of developing Alzheimer's disease.

The researchers carried out a study with 287 subjects and chose this hormone, which in the brain acts as a neurotransmitter, due to its high expression in the formation of a cognitive process such as memory.

Their objective was to detect whether there is a relationship between cholecystokinin levels and memory, and the state of gray matter in the hippocampus and other related brain areas.

At the same time, neuroscientists studied tau proteins (whose accumulation is related to the development of Alzheimer disease), with the aim of observing how they might interact with cholecystokinin and memory.

The results of the study concluded that as tau protein levels increased, a similarly high cholecystokinin level was no longer associated with less memory impairment.

This research highlights the importance of studying the nutritional aspect of diets, as well as their relationship with the mental health and its implication in the prevention of cognitive deterioration and neurodegenerative disorders such as Alzheimer's.