In peripheral tissues, the H1 subclass of histamine receptors mediates the contraction of smooth muscles, increase in capillary permeability due to contraction of terminal venules, and catecholamine release from adrenal medulla, as well as mediating neurotransmission in the central nervous system. Phosphorylation at sites in the second and third cytoplasmic loops independently contribute to agonist-induced receptor down-regulation. Belongs to the G-protein coupled receptor 1 family.