EXPOSING GUINEA-PIGS TO OZONE FOR 1-WK ENHANCES RESPONSIVENESS OF RAPIDLY ADAPTING RECEPTORS

Acute exposure to ozone causes changes in breathing pattern and lung f unction which may be caused in part by stimulation of rapidly adapting receptors (RARs). The consequences of repeated daily ozone exposure o n RAR responsiveness are unknown, although ozone-induced changes in pu lmonary function diminish with repeated exposure. Accordingly, we inve stigated whether repeated daily ozone exposure diminishes the general responsiveness of RARs. Guinea pigs (n = 30) were exposed to 0.5 parts /million ozone or filtered air (8 h/day for 7 days). The animals were then anesthetized, and RAR impulse activity, dynamic compliance (Cdyn) , and lung resistance were recorded at baseline and in response to fou r stimuli: substance P, methacholine, hyperinflation, and removal of p ositive end-expiratory pressure. Repeated daily ozone exposure exagger ated RAR responses to substance P, methacholine, and hyperinflation wi thout causing physiologically relevant effects on baseline or substanc e P- and methacholine-induced changes in Cdyn and lung resistance. Bec ause agonist-evoked changes in RAR activity preceded Cdyn changes, the data suggest that repeated daily ozone exposure enhances RAR responsi veness via a mechanism other than changes in Cdyn.