What is Histamine?

You must have heard the term “antihistamines” whenever someone is having an allergic reaction. Antihistamines suppress the effects of histamines, which give you the itchy feeling when something wrong enters your body. This is because they work to regulate your body’s immunity. Apart from being involved in the immune system,these substances also form components of the nervous and endocrine systems of your body. 

The term “amine” present in its name refers to the -NH₂, or “amino” group. This group is important in the classification of several biochemicals and the kinds of chemical reactions they carry out. Most of these substances are synthesized in certain immune cells called “basophils.” Others are synthesized in the thalamus and certain endocrine cells in the stomach. Based on their site of synthesis, histamines carry out the functions of that particular system.

Responsibilities:

Physically, histamines have a tiny structure, consisting of only 17 atoms. Despite this, they can efficiently work in key physiological systems. Moreover, their small structures make them more flexible, bind easily with specific receptors, and pass through membranes easily. Let’s look at the different functions carried out by these tiny molecules.

  • Neurotransmitters

Histamine is produced in the neurons of hypothalamus. Here, they work as neurotransmitters, which are chemical messengers that carry a nerve response. The hypothalamus, as we know, controls the sleep cycle. In this region, the histamines promote wakefulness. They are found at their highest concentration in an alert and awake state and at their lowest during the deep sleep stage. That is why, when antihistamine is given to a person, they feel drowsy.

  • Immune system messengers

Whenever a foreign particle, i.e., an allergen, enters the body, several cells of the immune system need to be activated. Chemical messengers carry this information to other cells. Histamine is one of these messengers. It binds to the epithelial cells, normally present at the inner lining of any organ, here blood vessels. These cells then contract, resulting in dilated blood vessels, which in turn decrease the blood pressure. Dialated blood vessels mean leakage of fluid in the tissues. Hence, you have typical reactions to allergy like runny nose, watery eyes, sneezing, etc.

  • Gastric acid release

As mentioned earlier, histamines are also produced in the stomach. Here, they trigger the production of stomach acid by binding to certain receptors. You must be familiar with antacid drugs like rantidine. These drugs block the histamine receptor, thus preventing more acid from being released in the stomach.  

How does It Work?

If you carefully observe the working of histamines, you will find that they work as messengers in all the systems. They bind to a particular receptor, which triggers an action. Depending on the required function, these receptors are numbered from 1-4. The functions of these groups are listed below:

  • H1- causes allergic response via the peripheral nervous system
  • H2- releases digestive acid and causes a decrease in the immune response.
  • H3- it is found in the central nervous system and regulates other neurotransmitters.
  • H4- it is found in immune cells and is related to allergic reactions.

As you saw in this blog, these little molecules control important aspects, including the nervous system. Just by altering their levels, they can cause significant changes, which can either be harmful or beneficial. Hence, there must be a correct balance of histamines in your body.