Histamine is one of the most important elements in the world of medicine, and its use is common when treating health problems, especially allergic reactions.
Throughout this article we will see what exactly histamines are and its effects on the human body.
Histamine is a molecule that acts in our body both as a hormone and a neurotransmitter, to regulate different biological functions.
It is present in significant quantities in both plants and animals, and It is used by cells as a messenger In addition, it has a very important role both in allergies and in cases of food intolerance and in the processes of the immune system in general. Let’s see what its secrets and most important features are.
History of the discovery of this imidazole amine
Histamine was first discovered in 1907 by Windaus and Vogt, in an experiment where they synthesized it from imidazole propionic acid, although they did not know that it existed naturally until 1910, when they saw that the ergot fungus manufactured it.
From this they began to study its biological effects. But It was not until 1927 when it was finally discovered that histamine is found in animals and the human body This occurred when physiologists Best, Dale, Dudley and Thorpe managed to isolate the molecule from a fresh liver and lung. And this is when it received its name, since it is an amine that is significantly found in tissues (histo).
histamine synthesis
Histamine is a B-amino-ethyl-imidazole, a molecule that is manufactured from the essential amino acid histidine, i.e. This amino acid cannot be generated in the human body and must be obtained through diet The reaction used for its synthesis is a decarboxylation, which is catalyzed by the enzyme L-histidine decarboxylase.
The main cells that produce histamine are mast cells and basophils, two components of the immune system that store it inside granules, along with other substances. But they are not the only ones that synthesize it, the enterochromaffin cells of both the pylorus region and the neurons of the hypothalamus area also do so.
Mechanism of action
Histamine is a messenger that acts as both a hormone and a neurotransmitter, depending on which tissue it is released in. As such, The functions it activates will also be carried out thanks to the action of histamine receptors Of the latter there are up to four different types, although there may be more.
This type of receptor is distributed throughout the body. It is located in the smooth muscle of the bronchi and intestine, where the reception of histamine causes bronchoconstriction and increased bowel movements, respectively. It also increases mucus production by the bronchi.
Another location of this receptor is found in the cells that form blood vessels, where it causes vasodilation and an increase in permeability. Leukocytes (that is, cells of the immune system) also have H1 receptors on its surface, which serve to target the area where histamine has been released.
In the Central Nervous System (CNS), histamine is also captured in different areas by H1, and this stimulates the release of other neurotransmitters and acts in different processes, such as sleep regulation.
2. H2 Receiver
This type of histamine receptor It is located in a group of specific cells in the digestive tract, specifically the parietal cells of the stomach Its main function is the production and secretion of gastric acid (HCl). Taking the hormone stimulates the release of acid for digestion.
TIt is also located in cells of the immune system, such as lymphocytes, favoring its response and proliferation; or in the mast cells and basophils themselves, stimulating the release of more substances.
3. H3 Receiver
This is a receptor with negative effects, that is, it inhibits processes when receiving histamine In the CNS, the release of different neurotransmitters, such as acetylcholine, serotonin or histamine itself, decreases. In the stomach it inhibits the release of gastric acid, and in the lung it prevents bronchoconstriction. Thus, as is the case with many other elements of the organism of the same type, it does not fulfill a fixed function, but rather has several and these depend largely on its location and the context in which it works.
4. H4 Receiver
It is the last histamine receptor discovered, and It is not yet known what processes it activates There are indications that it presumably acts in the recruitment of blood cells, since it is found in the spleen and thymus. Another hypothesis is that it participates in allergies and asthma, since it is located in the membrane of eosinophils and neutrophils, cells of the immune system, as well as in the bronchus, so that it is exposed to many particles that arrive from outside and can generate a chain reaction in the body.
Main functions of histamine
Among its performance functions we find that it is essential for promote the response of the immune system and work at the level of the digestive system regulating gastric secretions and intestinal motility. Also acts on the central nervous system by regulating the biological rhythm of sleep among many other tasks in which she participates as a mediator.
Despite this, histamine is well known for another, less healthy reason, as it It is the main one involved in allergic reactions These are reactions that appear when the organism itself is invaded by certain particles foreign to it, and one can be born with this characteristic or it can be developed at some specific moment in one’s life, after which it rarely disappears. . A large part of the Western population suffers from allergies, and one of their main treatments is taking antihistamines.
We will now go into more detail about some of these features.
1. Inflammatory response
One of the main known functions of histamine occurs at the level of the immune system with the generation of inflammation, a defensive action that helps isolate the problem and fight it In order to initiate it, mast cells and basophils, which store histamine inside, need to recognize an antibody, specifically Immunoglobulin E (IgE). Antibodies are molecules produced by other cells of the immune system (B lymphocytes), and are capable of bind to elements unknown by the body, the so-called antigens
When a mast cell or basophil finds an IgE bound to an antigen, it initiates a response against it, releasing its contents, including histamine. The amine acts on nearby blood vessels, increasing blood volume through vasodilation and allowing fluid to escape to the detected area. In addition, it acts as chemotaxis on other leukocytes, that is, it attracts them to the place. All of this results in inflammation with its redness, heat, edema and itching, which are nothing more than an unwanted consequence of a process necessary to maintain a good state of health, or at least try to.
2. Sleep regulation
Histaminergic neurons, that is, those that release histamine, are located in the posterior hypothalamus and tuberomammillary nucleus. From these areas, they extend to the prefrontal cortex of the brain.
As a neurotransmitter, histamine prolongs wakefulness and reduces sleep, that is, it acts in the opposite way to melatonin. It has been shown that when you are awake, these neurons activate rapidly. During moments of relaxation or fatigue they work to a lesser extent and are deactivated during sleep.
To stimulate wakefulness, histamine uses H1 receptors, while to inhibit it it uses H3 receptors. So, H1 agonist and H3 antagonist drugs are a good way to treat insomnia And conversely, H1 antagonists and H3 agonists can be used to treat hypersomnia. This is why antihistamines, which are H1 receptor antagonists, have drowsy effects.
3. Sexual response
It has been seen that During orgasm there is a release of histamine in the mast cells located in the genital area Some sexual dysfunctions are associated with the lack of this release, such as the absence of orgasm in the relationship. Therefore, excess histamine can cause premature ejaculation.
The truth is that the receptor used to carry out this function is currently unknown and is a subject of study; It is probably a new one and about which more will have to be learned as research along this line progresses.
Major disorders
Histamine is a messenger that is used to activate many tasks, but It is also involved in anomalies that affect our health
Allergy and histamines
One of the main disorders and most commonly associated with histamine release is type 1 hypersensitization, a phenomenon better known as allergy
The allergy It is an exaggerated response to a foreign agent, called an allergen, which in a normal situation should not cause this reaction. It is said to be exaggerated, because very little amount is needed to generate the inflammatory response.
The typical symptoms of this abnormality, such as breathing problems or a drop in blood pressure, are due to the effects of histamine on H1 receptors. Thus, Antihistamines act at the level of this receptor, not allowing histamine to bind to them
Alimentary intolerance
Another anomaly associated with histamine is food intolerance. In this case, The problem occurs because the digestive system is unable to degrade the messenger found in food due to the absence of the enzyme that carries out this task, DiAmine Oxidase (DAO). This may have been deactivated by a genetic or acquired dysfunction, in the same way that dairy intolerance occurs.
Here The symptoms are similar to those of allergies, and it is believed that they occur due to an excess of histamine in the body. The only difference is that there is no presence of IgE, since mast cells and basophils do not participate. Histamine intolerance can occur more frequently if you suffer from diseases related to the digestive system.
Conclusions
Histamine is a substance that has effects far beyond its role in the inflammatory processes linked to allergies. However, in practice, one of its most interesting and useful applications is its ability to mitigate allergy events; For example, a relatively small histamine pill can make skin redness and itching caused by allergies fade away.
However, it must be taken into account that, as with all pharmacy products, It is advisable not to abuse these histamine pills, and that in certain severe allergy processes, it is necessary to resort to other types of treatments to solve them, such as injections; always, yes, in the hands of health personnel duly accredited to practice.
