How is histamine formed from the amino acid histidine?
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antihistamine
Antihistamines such as Benadryl (diphenhydramine) and Claritin (loratadine) can be purchased without prescriptions. Both of those agents act by blocking H1 receptors. However, whereas Benadryl binds to those receptors in the central nervous system (CNS), causing drowsiness, Claritin does not readily enter the CNS and thus does not normally cause drowsiness.
In the human body, histamine is formed from the amino acid histidine through a chemical process known as decarboxylation.12
Decarboxylation involves the removal of a carboxyl group from the histidine molecule. Once synthesized, histamine is stored primarily in the granules of mast cells and basophils, where it remains until it is released to participate in various physiological processes, including immune responses and neurotransmission.2