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. Involved in circadian rhythm of locomotor activity and exploratory behavior. Also involved in responsiveness to pertussis toxin through its control of susceptibility to histamine hypersensitivity and enhancement of antigen-specific delayed-type hypersensitivity responses. Phosphorylation at sites in the second and third cytoplasmic loops independently contribute to agonist-induced receptor down-regulation. Strains C3H/HeJ and CBA/J are resistant to vasoactive amine sensitization elicited by histamine (VAASH) which is induced by pertussis toxin. Belongs to the G-protein coupled receptor 1 family.