The Role of Mediators in the Response of the Canine Peripheral Lung to 1 ppm Ozone

We tested the hypothesis that the in vivo response of the canine peripheral lung to 1 ppm ozone is mediated, in part, by histamine and cyclooxygenase and lipoxygenase products of arachidonic acid metabolism. Ozone was delivered for 5 min to lobar segments through a wedged bronchoscope and resulted in a mean (+/- 1 SE) increase in collateral system resistance (Rcs) of 220.7 +/- 13.8% immediately after exposure. Four 5-min exposures of ozone to the same segments over a 3-h period yielded reproducible Rcs responses, i.e., tolerance to the exposure regimen was not exhibited. Analyses of bronchoalveolar lavage fluid obtained from the isolated segment 1 min after a single exposure to ozone indicated significant increases, compared with control, in mean concentrations of PGD2 (135.3 +/- 33.3 pg/ml versus 47.8 +/- 16.0; p less than 0.025) and histamine (1.43 +/- 0.19 ng/ml versus 1.18 +/- 0.17; p less than 0.05). Additionally, a molecule that exhibited high reactivity with LTB4 antibody was found in greater concentrations in ozone-exposed segments compared to controls (821.5 +/- 206.7 pg/ml versus 437.5 +/- 78.8; p less than 0.05). In contrast, the concentration of TxB2 was not significantly greater in ozone-exposed segments compared to controls (37.2 +/- 6.6 pg/ml versus 33.7 +/- 10.3; p less than 0.05). Cyclooxygenase inhibition (indomethacin, 5 mg/kg, IV) significantly inhibited the Rcs response by 32% (p less than 0.05) and histamine H1-receptor blockade (chlorpheniramine maleate, 5 mg/kg, IV) reduced the response by 30% (p less than 0.05). However, blockade of thromboxane synthetase (UK-37,248, 3 mg/kg, IV) had no significant effect on the ozone-induced response.(ABSTRACT TRUNCATED AT 250 WORDS)