histamine H1 receptor HRH1 Bphs protein A histamine receptor that is a translation product of the human HRH1 gene or a 1:1 ortholog thereof. IUPHARobj:262 HH1R Category=gene. Note: The preferred ligand is histamine. This receptor mediates smooth muscle contraction, NO formation, increased vascular permeability, and other diverse effects. [PMID:9311023] PR:000001422 H1R H1 histamine receptor PIRSF:PIRSF038644 histamine receptor