Histamines are simple chemical substances your immune system cells produce when reacting to an antigen, produced in response to foreign invaders like germs and bacteria. They are only produced in localized places (like wounds) and cause inflammation and a couple of other reactions.
This has some interesting effects. For instance, everyone’s had a stuffy nose from time to time. Your nasal congestion is caused by an inflammatory reaction to high blood histamines. Antihistamines, like Benadryl, can deactivate the histamines in your blood. Interestingly, vitamin C can do the same thing.
But histamines do much more than just make you miserable when you have a cold. They also regulate gastric activity and your sleep schedule, and perform numerous functions in your body that are not yet fully understood.
Histamine Receptors
Histamines are designed to seek out receptors on cells in specific parts of your body. The most common receptor is the H1 receptor, concentrated in parts of your body that might get injured – your hands and feet, your skin, muscles. Histamines occuring here cause inflammatory reactions – which is why your joints swell, your injuries turn red and heat up, or you get hives from skin irritations.
A second type of histamine is what the latest generation of stomach acid treatments target. These histamines seek out the H2 receptors, located in the stomach’s epithelial cells, which trigger the generation of stomach acid.
H3 receptors for histamine are found in the brain, where when triggered they decrease the release of serotonin, acetylcholine, and norepinephrine. This action is thought to be related to our proper sleep routine. Lately, however, it’s been found that schizophrenics tend to have lower than normal levels of histamines, leading some to wonder if this is part of the complex interaction that leads to mental illness.
A fourth type of histamine receptors, the H4, are found in the lower gastrointestinal tract and in the bone marrow. The action of these receptors is unknown.
There are also probably other types of histamine receptors. For instance, mast cells in human genitalia release histamines during sex, and a lower-than-normal release has been related to several types of sexual dysfunction.
When You Take Antihistamines
The complex actions of histamines, affecting so many parts of the body, can be blocked by specific antihistamine drugs that attack primarily the receptors histamines attach to. Tagamet and Zantac, for instance, block the action of H2 receptors, lowering the level of acid produced in the stomach. Benadryl acts primarily on H1 receptors, but also has an effect on H3 receptors, resulting in decreased allergy symptoms but also a tendency to fall asleep.
While antihistamines are necessary in some cases (such as potentially fatal allergic reactions), because histamines are not fully understood antihistamines should be taken in moderation. There is some evidence, discovered recently, that the acid-blocker antihistamines like Zantac may contribute to or worsen Alzheimer’s symptoms, probably due to a previously-unknown effect on H3 receptors.
