Airway responsiveness to methacholine and airway smooth muscle in the guinea pig

The purpose of this study was two-fold: (1) to examine the relationship between the amount of airway smooth muscle and the airway responsiveness to inhaled aerosolized methacholine (MCh) in guinea pigs, and (2) to characterize the distribution of airway narrowing following MCh.In summary: (1) the quantity of airway smooth muscle (ASM) does not appear to determine differences in maximal bronchoconstriction among normal guinea pigs; the lack of a correlation between responsiveness and amount of ASM may be explained by the heterogenous distribution of bronchoconstriction among the airways studied or the modality of challenge; (2) the sensitivity to MCh appears to be related to differences in the amount of ASM in intraparenchymal cartilaginous airways; (3) variability in the EC$ sb{50}$ may also reflect differences in airway cross-sectional area; (4) lung resistance appears to be a good measure of constriction since the morphometric measure of airway narrowing correlated well with resistance; (5) the heterogeneity of airway narrowing does not appear to be determined by differences in ASM