Exposing guinea pigs to ozone for 1wk enhances responsiveness of rapidly adapting receptors

Acute exposure to ozone causes changes inbreathing pattern and lung function which may be caused in part bystimulation of rapidly adapting receptors (RARs). The consequences ofrepeated daily ozone exposure on RAR responsiveness are unknown,although ozone-induced changes in pulmonary function diminish withrepeated exposure. Accordingly, we investigated whether repeated daily ozone exposure diminishes the general responsiveness of RARs. Guineapigs (n = 30) were exposed to 0.5 parts/million ozone or filtered air (8 h/day for 7 days). The animalswere then anesthetized, and RAR impulse activity, dynamic compliance(Cdyn), and lung resistance were recorded at baseline and in responseto four stimuli: substance P, methacholine, hyperinflation, and removalof positive end-expiratory pressure. Repeated daily ozone exposureexaggerated RAR responses to substance P, methacholine, andhyperinflation without causing physiologically relevant effects onbaseline or substance P- and methacholine-induced changes in Cdyn andlung resistance. Because agonist-evoked changes in RAR activitypreceded Cdyn changes, the data suggest that repeated daily ozoneexposure enhances RAR responsiveness via a mechanism other than changes in Cdyn.