Changes in airway permeability and responsiveness after exposure to ozone

The purpose of this investigation was to examine the relationship between airway responsiveness and the permeability of histamine through the airways in conscious sheep after exposure to ozone (O₃). Airway responsiveness was assessed by measuring the change from baseline in mean pulmonary flow resistance following a controlled 2-min inhalation challenge with 1% histamine, containing 200 μCi/ml of [³H]histamine. The rate of appearance of the [³H]histamine in the plasma during inhalation challenge was used to estimate airway permeability. To perturb the airways, conscious sheep were exposed to either 0.5 or 1.0 ppm O₃ for 2 hr via an endotracheal tube. Airway responsiveness and airway permeability were measured prior to and 1 day after exposure. In six sheep exposed to 0.5 ppm O₃, increased airway responsiveness and airway permeability were observed 1 day after exposure. Four of seven sheep exposed to 1.0 ppm O₃ had enhanced airway responsiveness and airway permeability, while the remaining three sheep showed corresponding decreases in airway responsiveness and airway permeability. Since the O₃-induced directional changes in airway responsiveness paralleled the directional changes in airway permeability in both the positive and negative directions, it was concluded that changes in airway responsiveness to inhaled histamine following exposure to O₃ may be related to concomitant changes in airway permeability to this agent.