Differences between inhaled and intravenous carbachol in detecting O3-induced airway effects ☆

Abstract The response of specific lung resistance (SR L ) to inhalation of 5 and 10 mg/ml carbachol was compared with the response of SR L to intravenous infusion of 2 and 5 μg/kg carbachol before and after a 2-day exposure to 0.5 ppm ozone (O 3 ) in eight conscious sheep. Airway reactivity was defined as the slope of the dose-response curve and airway sensitivity as the largest increase in SR L after carbachol challenge. O 3 exposure did not alter mean airway reactivity or mean airway sensitivity as determined by inhalation challenge. In contrast, O 3 exposure significantly increased mean airway reactivity by 34% ( P P 3 exposure to enhance responsiveness to inhaled carbachol may have been related to decreased airway penetration of the aerosol, possibly due to mucus hypersecretion. However, O 3 exposure may have had a direct effect on the airway smooth muscle, thereby explaining the increased response to infused carbachol.