What Is a Histamine Antagonist?

Histamine is an active amine compound. As a chemically conductive substance in the body, it can affect the response of many cells, including allergies, inflammatory reactions, gastric acid secretion, etc., can also affect nerve conduction in the brain, causing the body to want to sleep and other effects. Histamine is decarboxylated from histidine. May be a neurotransmitter in the mammalian central nervous system. ^[1]

Histamine is an important physiologically active medium that is catalyzed by the decarboxylation of L-histidine by histidine decarbox-ylasc (HDC). Not only plays an important role in allergic reactions, but also plays an important role in the host's defense response to pathogenic microorganisms and in the immune regulatory response, which can affect the response of many cells. ^[2]

Histamine is present in

Why are some people allergic to fish? Taiwan is surrounded by the sea and is rich in fisheries. People who want to eat fish can buy it everywhere. However, some people are allergic to fish. As long as they eat a little fish, allergies such as rashes and itchy skin may occur. Where is it In general, people who are allergic to fish, even if they only eat a little fish, will have allergic symptoms such as flushing of the face, itching, rashes, and headaches.

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Animal tests have shown that guinea pigs injected with healthy human serum can avoid animal deaths caused by inhalation of histamine aerosol. The results were the opposite for those injected with allergic patient serum. If histamine is combined with non-specific equine serum globulin to histamine azoprotein (Azo-protein) complex, immune guinea pigs can also have a significant protective effect against anaphylactic shock. In addition, Parrot et al. Reported that subcutaneous injection of histamine globulin in guinea pigs can also cause animals to develop resistance to histamine aerosol inhalation, while human -globulin was injected into guinea pigs alone.

antihistamines

A class of drugs that can antagonize histamine. Histamine is a medium released by mast cells during rapid allergic reactions, which can cause capillary dilatation and increased permeability, smooth muscle spasm, and enhanced secretory activity, etc .; clinically, it can cause local congestion, edema, and increased secretion. Bronchial and digestive tract smooth muscle contraction, increase respiratory resistance, abdominal cramps, and can cause uterine contractions, manifested as dysmenorrhea, abortion and so on.

Histamine must first bind to histamine receptors or zymogen substances on the cells before it can function. Histamine receptors are of two types: H1 and H2. Generally speaking, antihistamines refer to H1 receptor antagonists, which can antagonize the effects of histamine on capillaries, smooth muscle, respiratory secretory glands, salivary glands, and lacrimal glands. H2 receptor antagonists mainly inhibit gastric secretion. Commonly used H1 receptor antagonists are chlorpheniramine, diphenhydramine, desensitization, hydroxyzine, and astemazine; H2 antagonists include cimetidine, methiomiamine, and the like.

There are three known subtypes of histamine receptors: H1, H2, and H3 receptors. Histamine acts on the H1 receptor, causing smooth muscle contraction of the intestine, bronchus and other organs. It can also cause capillary dilation, leading to increased vascular permeability and local redness and itching. Histamine acts on the H2 receptor and causes increased gastric acid The excessive secretion of gastric acid is closely related to the formation of peptic ulcer; the role of H3 receptors is still being studied.

Antihistamines can be divided into H1 receptor antagonists and H2 receptor antagonists. The former is mainly used for anti-allergy. The latter is mainly used for anti-ulcer.

Histamine use

Antihistamines have a wide range of clinical uses because they are easy to make, cheap, convenient to administer, and effective against a variety of allergic diseases. In addition to treating rapid allergies, they are also commonly used to prevent drug reactions and blood transfusion reactions; most of these drugs have central inhibitory and anesthetic effects, so they are also used to help treat certain mental and neurological disorders; they have inhibitory effects on the vestibule, so It is suitable for occasions such as vertigo and motion sickness caused by Meniere's disease; in addition, it is also used as a general antipruritic, cough, analgesic, sedative, or as a pre-anesthetic medication. It has a poor antispasmodic effect on bronchial smooth muscle. This is because leukotriene contracts bronchial smooth muscle much more effectively than histamine during an asthma attack. Therefore, antihistamines are not the main drugs for the treatment of asthma. H2 receptor antagonists are mainly used to treat gastric and duodenal ulcers. Most H1 receptor antagonists have side effects that cause drowsiness, so drivers, aerial workers, and workers operating high-speed rotating machines should be used with caution. Sismin, terfenadine, etc. do not have this side effect.

Histamine pharmacological effects

Most antihistamines share a common ethylamine group with histamine: X-CH2-CH2-N. Antihistamines are classified into H1 receptor antagonists and H2 receptor antagonists based on their target cell receptors competing with histamine. There are two types of sleepiness and non-sleepiness according to whether there is central sedation. According to their chemical group types, they can be divided into amino hydrocarbon ethers, hydrocarbon amines, piperazines, ethylene diamines and phenothiazines. The antihistamine effect of various antihistamines is different, and some have other pharmacological effects, including antiacetylcholine, antiadrenaline, and anti-serotonin. Antihistamines are quickly absorbed from the gastrointestinal tract and the injection site. Most preparations take effect within 30 to 60 minutes, maintain 4 to 12 hours, are hydroxylated in the liver and combine with glucuronic acid, and are excreted in the urine within 24 hours Only a small amount is discharged in its original form.