The hunger-inducing hormone Ghrelin together with the hormones leptin and cortisol regulates the feeling of hunger and satiety in animals and humans. In addition, it has an influence on numerous processes in the body, such as sleep behavior, stress reduction and blood circulation. There is still a need for research into the precise relationships.
What is ghrelin?
Ghrelin is a hormone that is produced in the lining of the stomach and pancreas. It was discovered in 1999. Its name comes from English and is an abbreviation for Growth Hormone Release Inducing, in German "Growth hormone release initiating".
It is a fat-insoluble hormone with a protein structure that consists of 28 amino acids. Its main function is to regulate the feeling of hunger and satiety. If no food has been ingested for a long time, the level of ghrelin in the blood increases and increases the feeling of hunger.
After eating, the level drops again. Ghrelin also regulates the formation of the growth hormone somatropin, which is produced in the pituitary gland and ensures normal physical growth.
Production, Education & Manufacturing
Glands in the lining of the stomach are primarily responsible for the formation of ghrelin. The hormone is also produced by cells in the pancreas.
A precursor to ghrelin is also produced in the brain, namely in the hypothalamus and pituitary gland. This hormone precursor is converted into the active form by splitting off some amino acids. Apparently, not only hunger leads to an increased release of ghrelin, but also shorter and poor sleep and other stress factors.
Function, effect & properties
Ghrelin regulates food intake by increasing hunger. It also slows down the metabolism and restricts the body from burning fat. Leptin and cortisol are also involved in controlling the feeling of hunger and satiety.
Cortisol is a stress hormone that makes appetite increase. Leptin sends the message to the brain that it should decrease appetite and burn more calories. In addition to its function in food metabolism, ghrelin has numerous other properties. It acts on a receptor in the pituitary gland that controls the release of growth hormone (somatropin). This means that growth hormone is released when you are hungry.
Somatropin is important for normal growth. If the production of somatropin is reduced during adolescence or if the cells do not respond adequately to it, physical growth will stop prematurely. In adults, somatropin regulates, among other things, the percentage of body fat and muscle mass as well as bone mineral density. In addition, it is believed that ghrelin in the hippocampus in the brain affects memory and learning ability.
A low ghrelin level ensures better memory performance. This mechanism is probably responsible for making learning easier during the day than at night, as ghrelin secretion is increased during the night. Ghrelin also has an influence on sleep behavior and the deep sleep phases. It is therefore believed that people who sleep poorly or too little have a greater tendency to become overweight.
Ghrelin could also help relieve depression. The fear-reducing effect of the hormone, which is also responsible for reducing stress, has been confirmed in animal experiments. The effects of the hormone on sleep behavior, stress reduction and blood circulation are complex and have not yet been conclusively researched. There is also still a need for research into the interaction with other hormones such as leptin and cortisol.
Illnesses, ailments & disorders
Presumably, ghrelin plays a role in the development of obesity, as the ghrelin level in the blood increases when you are hungry. In the case of overweight people, contrary to expectations, it was found that they do not produce too much, but too little ghrelin. Possibly higher body weight leads to an increased sensitivity to ghrelin, so that only small amounts are necessary to trigger a feeling of hunger.
However, there is still a need for research in order to finally clarify this question. Since a lack of sleep leads to increased ghrelin secretion, poor sleep is likely to contribute to the development of obesity. Stress also leads to an increased ghrelin level and thus forms another factor in the development of obesity. It has also been found that increased ghrelin levels due to stress make the brain more sensitive to traumatic experiences, which can be linked to the development of post-traumatic stress disorder.
In addition, ghrelin has been shown to be one of the factors that contribute to the development of alcohol addiction. Animal experiments showed that mice that were injected with ghrelin drank more alcohol than other mice. In the rare Prader-Willi syndrome, there are sometimes very high ghrelin levels. This disease is associated with a lack of satiety. The cause is a genetic feature that leads to a malfunction in the diencephalon.
The excessive feeling of hunger in these patients often leads to severe obesity and consequential damage such as diabetes mellitus. As a result, they have a shortened life expectancy. Elevated values can also be found in anorexia. In this case, the high ghrelin level does not lead to an increased feeling of hunger, but the patients are apparently resistant to the hunger-inducing effects of the hormone.
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