H1reseptorin

The H1 receptor, also known as the H1 receptor (HRH1), is a histamine receptor that belongs to the family of G protein-coupled receptors. It binds histamine and mediates many physiological responses related to allergy and inflammation, as well as roles in the central nervous system.

Signaling and function

H1 receptors predominantly couple to Gq/11 proteins, activating phospholipase C. This leads to production of inositol trisphosphate and diacylglycerol, resulting in increased intracellular calcium and downstream signaling. In the brain, H1 receptors influence arousal, attention, and other features of CNS activity. In peripheral tissues, receptor activation contributes to endothelial relaxation, increased vascular permeability, smooth muscle contraction, and itch sensation.

Distribution and physiological roles

H1 receptors are expressed on vascular endothelial cells, vascular smooth muscle, various immune and nerve cells, and neurons in the CNS. In the endothelium, H1 activation promotes nitric oxide–mediated vasodilation and increased permeability. In the airways, receptor activation can cause bronchoconstriction and mucus production. In the skin, H1 signaling mediates itch and inflammatory responses. In the brain, they participate in wakefulness, appetite regulation, and other neural processes.

Pharmacology and clinical relevance

H1 antagonists block histamine binding and are used to treat allergic rhinitis, urticaria, conjunctivitis, and other allergic conditions. First-generation antagonists (for example, diphenhydramine) cross the blood-brain barrier and can cause sedation, while second-generation agents (such as cetirizine and loratadine) are less sedating. Some H1 antagonists also possess antiemetic properties. Genetic variations in HRH1 can influence receptor function and drug responses.

Notes

The H1 receptor is a seven-transmembrane GPCR encoded by the HRH1 gene and is a key target in antihistamine therapy.