Histamine is a naturally occurring chemical, against which antihistamine drugs work. The reason why these medications are so popular among allergic people is that the production of histamine is the main cause of sneezing, congestion and irritation and itching of the eyes, associated with most allergies.
Histamine is released by immune cells called mast cells, or mast cells, to increase the blood supply in a lesion or respond to the presence of a foreign substance in the body.
What is histamine?
Histamine is an inflammatory chemical that occurs naturally in the body, and is also found in plants, bacteria, and the venom of insects. In humans, it is released by immune cells called mast cells, or mast cells, to increase the blood supply in a lesion or respond to the presence of a foreign substance in the body.
For people with allergies, histamine compounds can react to the presence of allergens such as dust, pollen, pet dander or mold, among others. However, histamine has a number of other functions.
It is present in most tissues of the human body and has a wide range of effects. It has been shown that:
• Involved in inflammation in the immune system • Acts as a messenger, or a neurotransmitter between neurons • Controls the secretion of gastric acid in the digestive system • Influences cell growth • Regulates contraction of soft muscles in the lungs, stomach, and uterus • Dilates blood vessels, which helps lower blood pressure and allows immune cells and fluids to travel to the lesion or infection • Increases heart rate Histamine Receptors
Histamine causes its effects on the body by joining, first, to one of the three types of receptors, which are found on the surface of cells.
Receptors are proteins that bind to messenger molecules such as histamine. When histamine binds to one of its receptors, the receptor signals the cell to act. The cell then responds according to its function. For example, a cell in the stomach with histamine receptors will respond to the presence of histamine by releasing gastric acid to aid in digestion.
H1 receptors are those attacked by over-the-counter antihistamines, also called H1 antagonists. Some examples of H1 antagonists are Zyrtec, Claritin, and Allegra. The H1 receptors are responsible for the most common symptoms of allergies and the most appropriate immune response to foreign bodies.
The H2 receptors are involved in the secretion of gastric acid and are involved in the acceleration of heart rate. H2 receptors are blocked by H2 antagonists, used as antacids (Tagamet, Zantac, Pepcid, etc.). Blocking this subtype of histamine receptor aids in the healing of peptic ulcers by decreasing the secretion of gastric acid in the stomach.
H3 receptors mediate the interactions between histamine and neurons in the brain and peripheral nervous system.
The role of histamine in the allergic response
Much of histamine is stored in special compartments, called granules, inside mast cells. It is also stored in granules of blood cells called basophils.
Substances that cause allergies such as pollen, animal dander, dust mites and mold spores cause the body to produce IgE antibodies. These antibodies recognize specific antigens. When antigen-IgE complexes bind to mast cells, the cells release excessive amounts of histamine. Histamine increases the permeability of blood vessels, allowing the fluid that contains the proteins of the blood and white cells to move to the nearest tissue.
This tissue swells and the symptoms of common allergies appear quickly (watery eyes, itching, runny nose and constricted airways).
The next time you sneeze and blow your nose during the pollen season, or observe skin rashes from a drug or food allergy, remember that histamine probably had a lot to do with the onset of these symptoms.
About the author
Boyan Hadjiev, M.D., has been a doctor for five years. He has a double certificate in Internal Medicine, (2003), and in Allergy and Immunology, (2005).
Dr. Hadjiev graduated from the University of Michigan with a bachelor's degree in biology, and an M.D. from the Western Reserve Medical School Cleveland Clinic-Case.