Hyperresponsiveness of airway muscle to acetylcholine in asthmatic and non-asthmatic subjects

Despite a long-standing recognition, the bronchial hyperresponsiveness (BHR) of airway smooth muscle, in asthmatic and non-asthmatic subjects is still under investigation.

In order to better understand the mechanism regulating the airway function, some results obtained with cellular physiology techniques are compared, for some non-asthmatic without BHR subjects and other subjects suffering from real bronchial asthma.

Eighteen subjects without chronic or acute bronchopathy and seven patients with a typical history of bronchial asthma were considered. All of them were non-smokers, with a wide range of in vivo hyperresponsiveness to Acetylcholine (ACh). Owing to neoplastic lesions, all patients underwent a thoracic surgery.

In vitro hyperresponsiveness of airway-smooth-muscle chains was assessed with isotonic contractions to incremental doses of ACh, in accordance with a non-cumulative dose-response technique. Regression between muscle contractions and ACh doses was studied for both groups, and it turned out to be linear in both cases. The slopes and elevations of the regression lines of the two groups were statically identical. There was no correlation between in vivo hyperresponsiveness (as PD20-ACh-FEV1) and in vitro responses (as EC50), for both asthmatic and non-asthmatic group.

(i) in vitro, the same BHR of smooth-muscle resulted, for both asthmatic and non-asthmatic subjects, (ii) in vivo, a different BHR of the former group resulted. This can be explained with the peculiarity of the micro-environmental surrounding the bronchial tissue, not with an intrinsic defect of the isolated bronchial tissue.