Histamine is obtained by Reproductive system and histamine

Histamine(English) histamine) is a biogenic substance formed in the body during the decarboxylation of the amino acid histidine.

Histamine. General characteristics

Histamine - chemical compound 4-(2-aminoethyl)-imidazole, or b-imidazolyl-ethylamine. The gross formula is C 5 H 9 N 3 . The molar mass of histamine is 111.15 g/mol. Under normal conditions, histamine is colorless crystalline substance. The melting point of histamine is 83.5 °C, the boiling point is 209.5 °C. Histamine is highly soluble in water and ethanol, insoluble in ether. Histamine is resistant to concentrated of hydrochloric acid and cold twenty percent aqueous solution caustic soda.

Histamine is a neurotransmitter of the most important biological processes.

Histamine in the human body is a tissue hormone, a mediator that regulates the vital functions of the body and plays a significant role in the pathogenesis of a number of disease states. Histamine in the human body is in an inactive state. With injuries, stress, allergic reactions, the amount of free histamine increases markedly. The amount of histamine also increases when various poisons, certain foods, and certain drugs enter the body.

Free histamine causes spasm of smooth muscles (including the muscles of the bronchi and blood vessels), dilation of capillaries and a decrease in blood pressure, stagnation of blood in the capillaries and an increase in the permeability of their walls, causes swelling of the surrounding tissues and thickening of the blood, stimulates the release of adrenaline and increased heart rate.

Histamine exerts its action through specific cellular histamine receptors. Currently, there are three groups of histamine receptors, which are designated H 1 , H 2 and H 3 .

The normal content of histamine in the blood is 539-899 nmol / l.

Histamine plays a significant role in the physiology of digestion. In the stomach, histamine is secreted by enterochromaffin-like (ECL-) mucosal cells. Histamine stimulates the production of hydrochloric acid by acting on the H2 receptors on the parietal cells of the gastric mucosa. Developed and actively used in the treatment of acid-dependent diseases (gastric and duodenal ulcer, GERD, etc.) a number of drugs called H 2 -blockers of histamine receptors, which block the effect of histamine on parietal cells, thereby reducing the secretion of hydrochloric acid in lumen of the stomach.

Histamine is a stimulant gastric secretion at diagnostic procedures Oh

Histamine is used as a stimulant in diagnostic procedures to evaluate functional state stomach: with fractional sounding or intragastric pH-metry. In clinical practice, either simple histamine test , or Kay's maximum histamine test . In the first case, the patient is injected subcutaneously with a 0.1% solution of histamine dihydrochloride at the rate of 0.008-0.01 mg per 1 kg of body weight, in the second case, 0.025 mg of histamine dihydrochloride is administered per 1 kg of body weight. At the same time, 45% and 90% of parietal cells are included in the work, respectively. The secretory effect of histamine begins in 7-10 minutes, reaching a maximum by 30-40 minutes and lasts 1-1.5 hours. To reduce the side effects of histamine (expansion of capillaries, an increase in the permeability of the walls of blood vessels, an increase in the tone of the smooth muscles of the bronchi), stimulation is carried out against the background of antihistamines: suprastin, diphenhydramine or tavegil, which are administered 1 ml parenterally half an hour before the introduction of histamine.

To stimulate gastric secretion in the study of the acid-producing function of the stomach, the diagnosticum "Histamine dihydrochloride", 0.1% solution for injection (production of Biomed named after I.I. Mechnikov, Moscow region, Petrovo-Far) or a similar preparation is used.

Professional medical publications concerning the use of histamine as a stimulant of gastric secretion in the study of gastric acidity:

• Rapoport S.I., Lakshin A.A., Rakitin B.V., Trifonov M.M. pH-metry of the esophagus and stomach in diseases of the upper digestive tract / Ed. Academician of the Russian Academy of Medical Sciences F.I. Komarov. - M.: ID MEDPRAKTIKA-M. — 2005. - 208


• Stupin V.A., Siluyanov S.V. Violation of the secretory function of the stomach in peptic ulcer // Russian Journal of Gastroenterology, Hepatology, Coloproctology. - 1997. - No. 4. - p. 23-28.


• Leya Yu.Ya. pH-metry of the stomach. Chapter 6 - L .: Medicine, 1987. - 144 p.


• Belmer S.V., Gasilina T.V., Kovalenko A.A. Intragastric pH-metry in pediatric gastroenterology. Methodical aspects. Second edition, revised. - M.: RGMU. - 2001. - 20 p.


• Dubinskaya T.K., Volova A.V., Razzhivina A.A., Nikishina E.I. Acid production of the stomach and methods for its determination. Tutorial. - M.: Russian Medical Academy of Postgraduate Education, 2004, - 20 p.


• Sablin O.A., Grinevich V.B., Uspensky Yu.P., Ratnikov V.A. Functional diagnostics in gastroenterology. Teaching aid. St. Petersburg. 2002

On the site in the "Literature" section there is a subsection " Secretion, digestion in the gastrointestinal tract",Containing articles for healthcare professionals on this topic.

Histamine is a drug

As a drug, histamine is currently rarely used.

Indications for the use of histamine are: polyarthritis, articular and muscular rheumatism, allergic diseases, migraine, pain caused by damage to peripheral nerves.

Dosage form: trade name "Histamine dihydrochloride", is produced (produced earlier) in the form of a solution for injection of 0.1%.

Ceplene is registered in the US with active substance histamine dihydrochloride for the treatment of acute myeloid leukemia.

Histamine is a biologically active substance involved in the regulation of many functions of the body and is one of the main factors in the development of some pathological conditions- in particular, allergic reactions.

Where does histamine come from?

Histamine in the body is synthesized from histidine - one of the amino acids, which is an integral component of the protein. In an inactive state, it is part of many tissues and organs (skin, lungs, intestines), where it is contained in special mast cells (histiocytes).

Under the influence of some factors, the transition of histamine to active form and release from cells into the general circulation, where it exerts its physiological action. Factors leading to the activation and release of histamine can be trauma, burns, stress, the action of certain drugs, immune complexes, radiation, etc.

In addition to the "own" (synthesized) substance, it is possible to obtain histamine in food. These are cheeses and sausages, some types of fish, alcoholic beverages, etc. The production of histamine often occurs under the action of bacteria, so there is a lot of it in long-term stored products, especially at insufficiently low temperatures.

Certain foods can stimulate the production of endogenous (internal) histamine - eggs, strawberries.

The biological action of histamine

Active histamine, which enters the bloodstream under the influence of any of the factors, has a quick and powerful effect on many organs and systems.

Main effects of histamine:

• Spasm of smooth (involuntary) muscles in the bronchi and intestines (this is manifested, respectively, by abdominal pain, diarrhea, respiratory failure).
• The secretion of the “stress” hormone adrenaline from the adrenal glands, which increases blood pressure and increases the heart rate.
• Increased production of digestive juices and secretion of mucus in the bronchi and nasal cavity.
• The impact on the vessels is manifested by the narrowing of large and the expansion of small blood paths, increasing the permeability of the capillary network. Consequence - swelling of the mucosa respiratory tract, hyperemia of the skin, the appearance of a papular (nodular) rash on it, a drop in pressure, headache.
• High levels of histamine in the blood can cause anaphylactic shock, in which convulsions, loss of consciousness, vomiting develop against the background of a sharp drop in pressure. This condition is life-threatening and requires emergency care.

Histamine and Allergy

A special role is given to histamine in the external manifestations of allergic reactions.

In any of these reactions, the interaction of the antigen and antibodies occurs. An antigen is a substance that has already entered the body at least once and caused hypersensitivity. Special memory cells store data about the antigen, other cells (plasma cells) synthesize special protein molecules - antibodies (immunoglobulins). Antibodies have a strict correspondence - they are able to react only with a given antigen.

The subsequent intake of the antigen into the body causes an attack of antibodies that “attack” the antigen molecules in order to neutralize them. Immune complexes are formed - an antigen and antibodies fixed on it. Such complexes have the ability to settle on mast cells, which contain histamine in an inactive form inside special granules.

The next stage of the allergic reaction is the transition of histamine to its active form and the release from the granules into the blood (the process is called mast cell degranulation). When the concentration in the blood reaches a certain threshold, the biological effect of histamine, which was mentioned above, is manifested.

Reactions involving histamine are possible, similar to allergic reactions, but they are not really allergic (they lack antigen-antibody interaction). This may be in case of admission a large number histamine c food products. Another option is the direct effect of certain products (more precisely, the substances that make up them) on mast cells with the release of histamine.

Histamine receptors

Histamine exerts its effect by influencing special receptors located on the surface of cells. Simplified, you can compare its molecules with keys, and receptors with the locks that they unlock.

There are three subgroups of receptors, the impact on each of which causes its own physiological effects.

Histamine receptor groups:

1. H 1 receptors are found in the cells of smooth (involuntary) muscles, the inner lining of blood vessels and in nervous system. Their irritation causes external manifestations of allergies (bronchospasm, swelling, skin rashes, abdominal pain, etc.). The action of antiallergic drugs - antihistamines (diphenhydramine, diazolin, suprastin, etc.) - consists in blocking H 1 receptors and eliminating the effect of histamine on them.
2. H 2 -receptors contained in the membranes of the parietal cells of the stomach (those that produce hydrochloric acid). Drugs from the H 2 blocker group are used in the treatment peptic ulcer stomach, because they suppress the production of hydrochloric acid. There are several generations of medicines(cimetidine, famotidine, roxatidine, etc.).
3. H 3 -receptors located in the nervous system, where they participate in the conduction nerve impulse. The effect on the H 3 receptors of the brain explains the calming effect of diphenhydramine (sometimes this side effect is used as the main one). Often this action is undesirable - for example, when driving a vehicle, it is necessary to take into account possible drowsiness and a decrease in the reaction after taking antiallergic drugs. Currently developed antihistamines with a reduced sedative (calming) effect or its complete absence (astemizole, loratadine, etc.).

Histamine in medicine

The natural production of histamine in the body and its intake with food play an important role in the manifestation of many diseases, especially allergic ones. Allergy sufferers have been noted to have elevated histamine content in many tissues: this can be considered one of the genetic causes of hypersensitivity.

Histamine is used as remedy in the treatment of some neurological diseases, rheumatism, in diagnostics, etc.

However, in most cases medical measures aimed at combating the undesirable effects that histamine causes.

Everyone knows what an allergic reaction is, but how histamine is associated with it remains a mystery shrouded in darkness for many. Few have at least some idea about histamine itself, which is a biologically active substance.

Histamine is involved in the regulation of most of the processes that occur in the body of any person. This substance is also a very important factor, without which the development of conditions associated with allergic reactions would not have occurred.

Histamine is synthesized in the human body from an amino acid called histidine, which is a constituent of protein. It has been scientifically proven that being in calm state, histamine is part of most tissues and organs, where it is contained in special cells.

But as soon as any allergen appears, the activation process immediately occurs, which provokes a large release of histamine into the blood. It is immediately worth noting that the amount of this substance in all people is not the same and can vary significantly among themselves.

To find out approximate quantity histamine in the body is enough to pass a simple test. In order to conduct such a test, it is not necessary to visit a specialized medical institution and take a number of tests, it can be quite easily done at home. The test is as follows - slightly scratch your arm from the elbow to the wrist. After a certain amount of time, the scratch will turn red.

It is this reaction that indicates that histamine enters the damaged area of ​​\u200b\u200bthe skin, which contributes to the elimination inflammatory process. Pronounced redness and swelling that does not go away for a long time, which remain after a scratch, indicate that the level of histamine in the body is too high. Please note that this test is designed only to find out the approximate amount of histamine, it is best to contact a specialist for a detailed and accurate result.

If during a home test you find that your histamine is too high, you should immediately contact a specialized medical institution for detailed advice from an experienced specialist. This fact should not be ignored, since high level This substance can cause anaphylactic shock. Not getting an injection of adrenaline on time can cause significant harm to your health.

You can also reduce the level of this substance in the body by following a certain diet, which involves eating the following foods:

• dairy and curd products;
• bread;
• Hercules;
• sugar;
• olive or sunflower oil;
• red meat;
• fresh vegetables, the most accurate list is better to check with a nutritionist who will make an individual diet.

As for products such as alcohol, smoked meats, cheese, seafood, coffee, marinades and citrus fruits, their use is strictly prohibited. Of course, such a ban on these products applies only if the patient has high histamine, in all other cases there is no need to keep a diet.

It is known that the level of this substance can increase with the use of certain foods due to improper storage, canning or freezing. In this case, an allergy to such products may occur even in healthy person who had never had such a reaction before.

Basically, histamine is quickly inactivated, and all solitary and not pronounced symptoms disappear on their own without the use of any medications or a visit to a specialist. Reactions can be numerous, then an antihistamine drug should be used immediately. Do not take the medicine without reading the instructions for use in advance, as misuse can lead to suffocation, convulsions and even death.

Histamine in medicine

This substance is also used in medical practice for the successful treatment of certain types of diseases, as well as for a number of studies and diagnostics. So, for example, to assess the functionality of the stomach, a solution of histamine hydrochloride is used, which is diluted in a certain proportion. The purpose of this study is to stimulate the secretion of gastric juice. The main indications for the use of histamine, which acts as medicinal product:

• Polyarthritis;
• Migraine;
• myeloid leukemia;
• Muscular and articular rheumatism;
• Radiculitis;
• Bronchial asthma;
• Pain of nervous origin.

Only in the presence of one of the above diseases, a professional specialist will make a decision and prescribe histamine as a drug to the patient. In all other cases, you should not use the drug on your own. This medicine also has contraindications, and a number of side effects, in the presence of which the use of histamine is strictly prohibited.

A complete list of contraindications can be found not only at the doctor's appointment, but also in the instructions that are attached. The drug is highly not recommended if you have dystonia, hypertension, a violation of the normal functionality of the kidneys and heart, as well as pregnancy and lactation.

As for side effects, they include: severe and continuous headache, dizziness, fainting, diarrhea, convulsions, nausea, lowering blood pressure, blurred vision. This is far from full list side effects, which is why it is so important to follow the appointment of a specialist and use only the dosage that was prescribed by him at the reception. Follow all the recommendations and instructions, then you will not have any problems with treatment.

Many of us know that with allergies, the patient is prescribed drugs that should eliminate the effect of a substance such as histamine. one of the neurotransmitters (mediators) that regulate important functions of the human body. Histamine is localized in all cells of the body and under normal conditions is inactive. When the allergen penetrates, it is activated and released into the blood in a large volume. The amount of this substance varies from person to person.

How to determine the level of histamine?

To find out the approximate content of this substance in the body, you can pass a simple test. To do this, you need to slightly scratch your hand from the elbow to the wrist. After a while, the scratch will turn red. This suggests that histamine enters the damaged area, which helps to eliminate inflammation. The stronger the redness and swelling, the higher the content of histamine in the body. If skin changes are significant and do not disappear long time, means that a person has increased histamine.

Its concentration must be reduced, since a high level of this substance in the blood can provoke. This can be done with the help of a timely injection of adrenaline.

Histamine - what is it and how to reduce its concentration in the body?

In order for the body to eliminate the undesirable properties of inflammation, it is necessary to lower the concentration of histamine in the blood. This can be done with the help of a certain diet that excludes foods with a high content of this substance, such as:

• alcoholic beverages (particularly red wine);
• smoked products;
• yeast;
• seafood;
• cocoa, coffee;
• pickled vegetables and fruits;
• Wheat flour;
• citrus.

The following products are allowed:

• milk, cottage cheese;
• bread;
• oat flakes;
• sugar, vegetable oils;
• fresh meat;
• vegetables, except for tomatoes, spinach, cabbage, pumpkin, eggplant.

Histamine as a drug

So, we learned a lot about histamine: what it is, and what role it plays in the human body. But it turns out that this substance can be a cure. Indications for its use may be polyarthritis, migraine, muscular and joint rheumatism, sciatica, allergic reactions. In the latter case, the dose of histamine is gradually increased, thereby trying to achieve a more stable state of the body to various manifestations allergies. However, there are a number of contraindications to taking this substance, these include:

• heart disease;
• dystonia;
• hypotension;
• hypertension;
• respiratory diseases;
• impaired renal function;
• pheochromocytoma;
• pregnancy;
• lactation period.

Histamine intake can cause such side effects as a severe continuous headache, dizziness, fainting, cyanosis, diarrhea, convulsions, tachycardia, nervousness, shortness of breath, nausea, vomiting, a sharp decrease in blood pressure, reddening of the skin of the face, blurred vision, pain in chest, swelling of the injection site.

We hope that now you know the answer to the question: "Histamine - what is it?"

The concept of "histamine" is well known to those people who had to deal with an allergic reaction to something in their lives and take antihistamines. Therefore, many people think that histamine is itself. However, this is a misconception.

What it is

Histamine was first synthesized in 1907. When it comes to biological matter pure form, then it is a colorless crystal that can be dissolved in water or ethanol.

In general, it is a mediator of allergic reactions. The secretion of this biologically active substance is histidine.

In its normal state, in which it is always found in the body, this component is found in almost all cells. Science named it the histiocyte. It is then that it is safe and does no harm. If some factors influence it, it is able to activate and concentrate in the blood in large quantities.

At its core, it is a tissue hormone. Its main task is to report a problem in the body if there is a threat to health. The protection mechanism itself activates many systems. Therefore, knowledge of this system will help to understand true reasons allergies caused by nervoses, intolerance to certain products, reactions to stressful situations.

Today, the cause of a number of problems is the excessive activity of this biological substance, against which diseases develop, immunity decreases. At the same time, the person feels bad, but there are no visible reasons for this.

Histamine shows its activity if there are catalysts that provoke it to action. These factors include:

• trauma;
• burns;
• frostbite;
• stress;
• exposure;
• adverse reaction from taking medications;

The presence of a synthesized tissue hormone in the blood can be observed due to the consumption of certain foods. It is also abundant in frozen foods. At low temperatures, an increased amount of a substance appears in food.

Biological action and functions in the body

If a substance in an active state enters the bloodstream, then it has a strong effect on all human organs. Changes begin from its overabundance:

• breathing becomes difficult, bronchial spasms are possible;
• there is an upset stomach;
• adrenaline is released, which causes the heart to beat faster;
• the process of digestion is accelerated;
• pressure drops, headaches begin;
• at a high concentration in the blood, anaphylactic shock can occur - the pressure drops sharply, the person loses consciousness, convulsions and vomiting are possible.

The main functions of a chemical that interacts with almost all organs are a number of important life processes:

1. Regulates blood supply in organs and tissues. If a person works hard physically, then there may be a lack of oxygen in the muscles. This is where histamine comes into play. It causes the capillaries to expand, which leads to an increase in the flow of blood and oxygen.
2. Regulates the acidity of the stomach, in the mucosa of which it acts as a mediator. Stimulates cells capable of producing hydrochloric acid.
3. Regulates inflammation in the body.
4. nervous regulation. Histamine keeps the CNS awake. During a period of relaxation or fatigue, the activity of histamine neurons decreases, and during a short sleep, they completely stop their activity. The biological substance also protects the cells of the nervous system, prevents convulsions, ischemic damage, stressful situations in the central nervous system and helps to forget unnecessary information.
5. Regulates reproductive function and sex drive. The introduction of a biological substance into the body of a man with erection problems restored it by three-quarters. Therefore, if, for example, with the help of receptor antagonists, acidity in the stomach is also reduced, then one may encounter a loss of libido or even impotence.

There are women who suffer from intolerance to this tissue hormone. This is due to its interaction with female hormones and the ability of the hormone to provoke uterine contractions.

Where does it come from in the body?

Scientists have long known that histamine is produced from histidine. If to speak plain language, histidine is an amino acid found in almost all protein foods. People use them every day. You need to understand that all protein molecules are built in a certain order from 20 different amino acids. And already their properties will depend on the order in which they stand.

It is worth noting that histamine resides in the mast cells of human organs - the skin, intestines and lungs.

Histamine and Allergy

Histamine performs a special function in the manifestation of allergies. Here, in no case can it do without two substances that react with each other.

Antigen - the human body has already met with it. He memorized it and kept the information about his "stay". This substance has already entered the tissues and caused a certain irritability in the cells. All the information in the cells is already there, but here antibodies come into play. And you need to understand that this becomes the main catalyst for the appearance of allergies.

Now that the body is familiar with the antigen, antibodies begin to attack and neutralize it, merging together and getting to where histamine is located in special granules.

This is the most First stage allergic reaction. It is now followed by the active role of biological matter. Histamine enters the active phase. After immune complexes have entered the mast cells, it begins to leave the granules into the blood. And if its concentration in the blood reaches a certain level, then the reactions that were described above begin. That is why histamine is confused with the cause of allergies. In fact, he is just a conductor. It is difficult to imagine all the vital functions in the body without it.

There are also possible reactions that are very similar to allergies, but there is no tandem in the chain - an antibody and an antigen. This happens if an increased amount of a biologically active substance enters the body with food.

Histamine receptors

To date, only three groups of specific histamine receptors have been studied.

More about each:

1. H1. The receptors of this group are found in smooth muscles, in the lining of blood vessels from the inside and in the nervous system. These receptors are subject exclusively to external stimuli. Among allergic reactions are bronchial spasms, pain in the gastrointestinal tract, edema, increased vascular permeability. The biological substance that has been released from mast cells is a conductor and contributes to the appearance of eczema, urticaria, and allergic rhinitis. The effects that the receptors of this group have are narrowing of the airway lumen and muscle contraction in the gastrointestinal tract. Therefore, it is safe to say that the substance is involved in the occurrence of asthma and food allergies. Medications that block receptors inhibit allergic reactions. Due to the fact that the process of this inhibition will occur in the brain, experts call drowsiness one of the side effects of these drugs. Therefore, people who work in jobs that require concentration should carefully use these drugs. Drivers should especially pay attention to this fact.
2. H2. These receptors are located only in the cells of the stomach, if they are activated, then the production of gastric juice - enzymes and hydrochloric acid - begins to increase. To block the receptors of this group, it is necessary to take drugs - cimetidine, roxatidine.
3. H3. The receptors of this group are located in the cells of the PNS. They are responsible for conducting impulses and regulate the period of sleep and wakefulness. If there is an overabundance, then the person has problems with sleep, there is excessive overexcitation and the impossibility of relaxation.

Why is it dangerous for humans and how does it affect the body

Of course, there is no definite answer to this question. Histamine is a substance without which the body will not fully function.

It is more dangerous when in excess. So, for example, if it comes into contact with the pollen of flowers, then mucosal edema and nasal congestion may appear. If it is in contact with a large number of chemical allergens for a long time, it can cause skin diseases.

And there are reactions that are even dangerous to human life. What is only anaphylactic shock - a sharp decrease in pressure, loss of consciousness. The body can be brought out of this state only by blocking the production of the substance.

Destruction of histamine

Leaving its permanent habitat - mast cells, histamine is partially destroyed, however, part of the substance is sent back, where it again accumulates in granules. From where it can exit again when activated.

It is destroyed only under the influence of several basic enzymes. The reaction occurs in the central nervous system, intestines and partly in mast cells.

Part of the substance is excreted from the body with urine.

Pseudo-allergic reactions

Such, at first glance, similar to the usual allergy reactions, have nothing to do with the immunological nature. The main thing here is to understand that there is an antigen in the chain that is present in true allergies. And if a foreign organism is not detected in laboratory conditions, it means that there is an excess of a biologically active substance - histamine - in the body.

It can be obtained from food, and at first glance it will seem to you that you have an allergy to something - a rash on the skin, difficulty breathing, decreased pressure, arrhythmia, indigestion may appear. So foods rich in histamine, in this case, should be consumed without enthusiasm.

Foods high in this organic compound:

• Strawberry;
• hard cheese;
• lemon;
• a pineapple;
• eggs;
• tomatoes;
• walnuts;
• chocolate;
• oranges.

Here is one of the clearest examples. As a kind of pseudo-allergy - nervous. It comes without allergens. Everything laboratory research they don’t find the cause, and as soon as a person starts to get nervous, obvious signs of an allergy immediately appear. It occurs quite often.

The use of histamine in medicine

Very rarely, a patient is prescribed histamine-containing drugs in the treatment of rheumatism and certain neurological diseases.

Usually, with such appointments, an analysis is done to detect anaphylactic reactions.

Often, a decrease in the level of histamine concentration in the body is required. Among the drugs that can do this is dihydrochloride. It is administered intramuscularly in small doses. Used for:

• rheumatism, joint diseases, radiculitis;
• allergic diseases.

However, it has a number of contraindications:

• lactation period;
• pregnancy.

If you choose the right dose and bring everything back to normal, you can get rid of diseases caused by a high level of this biological substance.

Difficult but important

It is important to understand how it works, what functions it performs and what effect this tissue hormone has on the body. It is already clear that he is involved in many processes occurring in the body. It is impossible to assess its harm or benefit. Because without it, a person simply will not be able to immerse himself in a very important physiological process - sleep.

However, most of the activities in medicine are aimed at combating the undesirable effects that histamine has.