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8 February 2021

Histamine: the key to effective allergy treatment

The histamine molecule controls all kinds of bodily processes and plays the leading role in allergic reactions. It causes sneezing, tears and shortness of breath, in all degrees. In rare cases it can even lead to a fatal drop in blood pressure.

In 1907 the structure of histamine was discovered, and it had become clear that it must be a breakdown product of the amino acid histidine. Biochemist Henry Hallett Dale knew from animal experiments that a very small dose of histamine could cause a rapid and dangerous drop in blood pressure in some animals.

Sometimes it is also a bee sting, the stimulus that causes an overdose of histamine and then urgent action is required. Fortunately, this phenomenon is very rare. Besides a drop in blood pressure, histamine can also have many other effects. In the skin it causes redness, swelling and itching. In the airways it leads to sneezing, coughing, breathlessness and mucus formation. In the stomach it causes an increase in the amount of stomach acid. It is clear that histamine plays the leading role in all allergic reactions, be it nickel allergy, latex allergy, milk protein allergy or allergy to house dust. No matter how differently each allergy develops, the last step is always the same: histamine is released.

Lock and key
How can a signal substance such as histamine actually cause an effect at all? This has to do with certain proteins on the cell wall. Some of those proteins – the receptors – act like a switch. For example, they cause a muscle cell to contract, a stomach wall cell to produce stomach acid, or a nerve cell to transmit a stimulus.

Such a molecular switch does not look like a light switch, but more like a lock that can only be operated with the correct key. A receptor is switched by a molecule of a signal substance, which acts as a key. That molecule must have two properties: it must be able to anchor itself well to the receptor and then it must activate the receptor. In other words: the key must first fit into the keyhole, and then be able to turn, so that the lock opens.

With their knowledge of the mechanism of action of histamine, chemists have been looking for substances that block the receptor protein and thus counteract the action of histamine. Just as you can block a keyhole with chewing gum or the wrong key, you can block a receptor with a suitable molecule. That molecule must adhere well but not activate the receptor. A substance that can block the action of the signal substance histamine in this way is called an antihistamine. With such an antihistamine you can counteract the effects of histamine in the body (such as itching and asthma). At the moment, therefore, nobody has to suffer from the consequences of a hay fever attack. Use an antihistamine in time and the worst symptoms of hay fever are suppressed.

*Source: NEMO Kennislink