From the Guidelines
The H1 (histamine 1) receptor plays a crucial role in mediating allergic responses, particularly in the context of anaphylaxis and allergic rhinitis.
Key Functions of H1 Receptors
- Mediate allergic responses, including symptoms such as pruritus, flushing, and urticaria 1
- Involved in the pathophysiology of anaphylaxis, with H1 receptors being the most clinically relevant 1
- Play a key role in nasal obstruction in allergic rhinitis, inducing symptoms such as sneezing, nasal discharge, and nasal obstruction 1
H1 Receptor Antagonists
- First-generation H1 antihistamines, such as diphenhydramine, hydroxyzine, and chlorpheniramine, are effective in treating allergic symptoms but have limitations due to sedation and anticholinergic effects 1
- Second-generation H1 antihistamines, such as fexofenadine, loratadine, and desloratadine, are preferred due to their longer duration of action, less sedation, and fewer anticholinergic effects 1
Clinical Implications
- H1 receptor antagonists are often used as adjunctive therapy for anaphylaxis, but should not be administered before or in place of epinephrine 1
- In allergic rhinitis, H1 receptor antagonists can be used as monotherapy or in combination with other agents, such as intranasal corticosteroids, to manage symptoms 1
From the Research
Role of the H1 Receptor
The H1 receptor is a type of histamine receptor that plays a crucial role in various physiological and pathophysiological conditions. Some of the key functions of the H1 receptor include:
- Mediating the central effects of histamine on alertness and wakefulness 2
- Regulating the expression of pruritic factors, such as nerve growth factor and semaphorin 3A, in skin keratinocytes via histamine H1 receptor (H1R) 3
- Inducing pro-inflammatory effects on T cells, B cells, monocytes, and lymphocytes 4
- Mediating the bronchoconstrictive effects of histamine and increasing vascular permeability in the lung 4
Therapeutic Applications
The H1 receptor is a target for various therapeutic applications, including:
- Treatment of allergy and insomnia with H1 receptor antagonists 2, 5
- Relief of symptoms of allergic rhinitis with H1-receptor antagonists 4
- Potential treatment of atopic dermatitis with next-generation antihistaminic agents possessing H1R and H4R antagonistic actions 3
Mechanism of Action
The mechanism of action of the H1 receptor involves:
- Binding of histamine to the H1 receptor, which triggers a response 5
- Inverse regulation of the H1 receptor by antihistamines, which utilize a shared phenyl group to block the movement of the toggle switch residue W4286.48 5
- Potential introduction of new derivative groups to generate newer antihistamines through a secondary ligand-binding site in H1R 5