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H 1 antagonists, also called H 1 blockers, are a class of medications that block the action of histamine at the H 1 receptor, helping to relieve allergic reactions.Agents where the main therapeutic effect is mediated by negative modulation of histamine receptors are termed antihistamines; other agents may have antihistaminergic action but are not true antihistamines.
Histamine receptors are proteins that bind with histamine, a neurotransmitter involved in various physiological processes. There are four main types: H1, H2, H3, and H4. H1 receptors are linked to allergic responses, H2 to gastric acid regulation, H3 to neurotransmitter release modulation, and H4 to immune system function.
H1-antihistamines are further split into three groups known as the first-generation, second-generation and third-generation antihistamines. Another type of antihistamines known as H2-antihistamines are used to treat gastrointestinal conditions caused by excessive stomach acid. [8] Mechanism
Histamine H 1 receptors are activated by endogenous histamine, which is released by neurons that have their cell bodies in the tuberomammillary nucleus of the hypothalamus. The histaminergic neurons of the tuberomammillary nucleus become active during the 'wake' cycle, firing at approximately 2 Hz; during slow wave sleep , this firing rate ...
The most common antihistamines utilized for this purpose include hydroxyzine, promethazine (enzyme induction especially helps with codeine and similar prodrug opioids), phenyltoloxamine, orphenadrine, and tripelennamine; some may also have intrinsic analgesic properties of their own, orphenadrine being an example. Second-generation ...
Histamine is a ubiquitous messenger molecule released from mast cells, enterochromaffin-like cells, and neurons. [5] Its various actions are mediated by histamine receptors H 1, H 2, H 3 and H 4. The histamine receptor H 2 belongs to the rhodopsin-like family of G protein-coupled receptors.
H 1-receptor antagonists are competitive inhibitor of histamine receptor H 1 and are used to treat allergies. This group is often referred simply as antihistamines . Wikimedia Commons has media related to H1 receptor antagonists .
Cimetidine was the prototypical histamine H 2 receptor antagonist from which later drugs were developed. Cimetidine was the culmination of a project at Smith, Kline & French (SK&F; now GlaxoSmithKline) by James W. Black, C. Robin Ganellin, and others to develop a histamine receptor antagonist that would suppress stomach acid secretion.