The role of histamine in allergic rhinitis.

Studies using nasal provocation followed by nasal lavage have demonstrated that histamine plays an important role in the mediation of allergic rhinitis but not of rhinovirus infection. The response to antigen challenge is often biphasic. During the early response, increases in histamine levels appear to be associated with activation of mast cells. In a subset of persons who exhibit an additional late response, however, the rise in histamine is concomitant with an increase in the number of basophils. Further evidence of the role of histamine in allergic rhinitis has emerged from nasal provocation experiments involving pretreatment with a variety of drugs known to antagonize or affect release of histamine. Nasal provocation with histamine causes sneezing, itching, rhinorrhea, and nasal congestion. Most H1 antihistamines have been found to inhibit sneezing and to lessen the increase in vascular permeability, but they do not affect histamine release. The H1 antihistamine terfenadine, however, inhibits histamine release during the early response; effects on late response remain unknown. Prednisone decreases histamine levels during the late, but not the early, response. One-week pretreatment with topical steroids, on the other hand, affects both the early and the late response.