Changes in Upper and Lower Airway Resistance After Inhalation of Antigen in Sensitized Rats

Abstract

To assess the contribution of upper and lower airways to the changes in pulmonary resistance after inhalation of antigen by sensitized rats, we measured changes in upper airway resistance (Ru) and lower pulmonary resistance (Rlo) after inhalation of ovalbumin (OA) in anesthetized, spontaneously breathing, sensitized BN rats. Aerosols of antigen were inhaled through the nose and through a tracheostomy in random order; there was a 1-h recovery interval between challenges. After inhalation of OA through the nose, Ru increased from 0.441 ± 0.057 (mean ± 1 SE) to 1.342 ± 0.504 cm H₂O·ml⁻¹·s (n = 6; p < 0.05) and Rlo increased from 0.099 ± 0.017 to 0.269 ± 0.08 cm H₂O·ml⁻¹·s (p < 0.05). Changes in Ru and Rlo were strongly correlated (r = 0.938; p < 0.001). After OA was inhaled through the tracheostomy, Rlo increased from 0.089 ± 0.021 to 0.152 ± 0.041 cm H₂O·ml⁻¹·s (p < 0.05). However, Ru did not change significantly. Pretreatment of the lower airways with inhaled atropine did not affect the magnitude of the changes in Ru after inhalation of OA through the nose but significantly attenuated the response of the lower airways. We conclude that when sensitized, spontaneously breathing rats inhale antigen through the nose, (1) the predominant reaction occurs in the upper airways; (2) changes in upper airway resistance do not result from reflexes originating in the lower airways; (3) lower airway responses are mediated in part by cholinergic mechanisms.