In vivo, in vitro correlation of acetylcholine airway responsiveness in sensitized guinea pigs. The role of modified epithelial functions

Abstract

Many attempts have failed to correlate in vivo airway responsiveness with in vitro airway smooth muscle functions. We have reexamined this relation by taking account of airway epithelial functions in guinea pigs sensitized with inhaled ovalbumin (OA). In vivo responses were assessed by the provocative concentration of acetylcholine (ACh) required to double the airway opening pressure (PC200) under mechanical ventilation. In vitro responses were measured in a perfused whole-tracheal preparation. The negative logarithm of the molar concentration of ACh required to produce a 10% reduction in diameter was calculated both for epithelial-side stimulation (PC10(in)) and for serosal-side stimulation (PC10(out)). OA-sensitized guinea pigs showed significantly smaller log PC200 than control animals (0.51 +/- 0.07 and 0.81 +/- 0.10, respectively, p < 0.01). In in vitro study, there were variable differences in PC10(in) and PC10(out) in each animal. The difference in sensitivity between epithelial- and serosal-side stimulation (PC10(in-out)) showed a significant correlation in PC10(in) (r = 0.82, n = 9, p < 0.01) but not to PC10(out) (r = 0.39, p > 0.1), indicating that the variation in PC10(in-out) resulted from the changes in PC10(in). For in vivo-in vitro correlation, log PC200 correlated significantly with PC10(in) (r = 0.68, n = 9, p < 0.05) but not with PC10(out) (r = 0.18, p > 0.1). These results indicate that the sensitization by inhalation of OA produces increased airway responsiveness to ACh in vivo and that this airway responsiveness may be related, at least in part, to the altered airway epithelial functions.