Histamine is a molecule that is manufactured from an essential amino acid, histidine. Being an essential amino acid means that our body cannot manufacture it endogenously, therefore, it must be introduced through food. Its synthesis is carried out through a decarboxylation catalyzed by the enzyme L-histidine decarboxylase and the main cells responsible for its manufacture are mast cells and basophils, both components of the immune system.
It is the main one involved in the allergic reactions that appear before the invasion of the body itself by certain particles that are foreign to it, hence a large part of the population is medicated with antihistamines in times like autumn or spring when our immune system is look more engaged.
It acts as a neurotransmitter and will depend on the tissue in which it is released. There are 4 types of receptors, although there may be more.
H1 receptor: It is located throughout the body, in smooth muscle, in the bronchi and in the intestine, in blood vessels where it causes vasodilation and increased permeability, and in the central nervous system.
H2 receptor: it is located in the parietal cells of the stomach, whose main function is the production and secretion of hydrochloric acid, and in the lymphocytes, favoring their response and proliferation.
H3 receptor: it is a receptor with negative effects, that is, it produces an inhibition of the processes when receiving histamine.
H4 receptor: it is the last one that has been discovered and it is unknown what processes it activates. It is assumed that it could act in the recruitment of blood cells, since it is found in the spleen and thymus.
Relationship of histamine and the digestive system
The main functions of histamine are, among others, to promote the response of the immune system and to act in the regulation of gastric secretions and in the motility of the intestine.
In addition, it intervenes in the inflammatory response, generating inflammation that is nothing more than a defensive action whose purpose is to fight against basophils that contain histamine inside. These basophils need to recognize an antibody, specifically IgE, which are produced by B lymphocytes.
Inflammation is a protective mechanism that helps control infections, wound healing, therefore, inflammation is a necessary mechanism for the body, however, the situation changes when in certain situations such as reactions allergic or chronic diseases the inflammatory process becomes a pathogenic mechanism. Inflammation has two phases, acute and chronic. The acute phase has a brief course consisting of the exudation of fluid and plasma proteins and the migration of leukocytes (neutrophils). The chronic phase consists of a longer duration and is characterized by the proliferation of blood vessels, fibrosis and tissue necrosis.
When histamine cannot be metabolized by the DAO enzyme, it can lead to histaminosis, which in turn could compromise our liver, since due to intestinal permeability, many toxins would pass into the systemic circulation, and via the portal these toxins would reach the liver.
The liver is a very important organ whose functions are to filter, break down, and carry out the methylation of histamine. If there are high levels of histamine, its functional capacity will be seriously saturated and, as a consequence, stress hormones such as cortisol, histamine, estrogens will be elevated, and there will be a poor elimination of toxins from the body.