The relationship between plasma histamine concentrations and bronchial obstruction to antigen challenge in allergic rhinitis.

Antigen activation of pulmonary mast cells causes mediator release and airway obstruction in allergic patients with asthma. Concomitant measurements of airway mediators and pulmonary function are technically difficult, even with bronchoalveolar lavage. Thus, a procedure was developed to evaluate further the relationship between mediator release, as measured by plasma histamine concentrations, and airway obstruction in patients with allergic rhinitis challenged with inhaled ragweed antigen. At an initial challenge, the cumulative antigen dose to decrease the FEV1 by approximately 20% was determined. Approximately 4 weeks later, the entire predetermined cumulative antigen dose to decrease the FEV1 by approximately 20% was administered in five consecutive inhalations with simultaneous monitoring of plasma histamine. We found the percent fall in FEV1 (24.3 +/- 2.3 versus 30.4 +/- 4.0; p greater than 0.05; n = 7) was similar whether antigen was administered by a cumulative or single-dose challenge. With the single-dose antigen challenge and monitoring blood samples frequently, we found plasma histamine (picograms per milliliter) values to increase from 73 +/- 17 to 1071 +/- 377 (p = 0.022) with peak value 5 minutes after challenge. Furthermore, we found that the intensity of airway obstruction to antigen corresponded to both the patient's baseline airway responsiveness to histamine and the absolute changes in plasma histamine after antigen challenge. Thus, the degree of airway obstruction to inhaled antigen is determined by both the intensity of the allergic reaction (as reflected by the plasma histamine value) and bronchial responsiveness.