Is there loss of a protective muscarinic receptor mechanism in asthma?

L. E. Ayala, T. Ahmed

Research output: Contribution to journalArticlepeer-review

90 Scopus citations


We investigated the hypothesis that prior airway muscarinic receptor stimulation (with aerosolized methacholine) would modify the bronchoconstrictor response to histamine, which is, in part, vagally mediated. On four different experiment days, the following combinations of methacholine and histamine inhalation challenges were performed in 15 subjects (nine normal and six asthmatic) in a random fashion: methacholine-histamine, histamine-methacholine; methacholine-methacholine and histamine-histamine. Cumulative provocative dose of each agonist which caused a 50 percent decrease in SGaw was estimated (PD50). The second challenge was performed approximately 1 hour after the first challenge, when SGaw had returned to baseline. In normal subjects, prior muscarinic stimulation with methacholine suppressed the subsequent bronchoconstrictor response to histamine (mean ± SE PD50 histamine increased from 13.7 ± 3.1 to 28.4 ± 7.2 breath units), without modifying the bronchoconstrictor response to methacholine. In asthmatic subjects, prior methacholine exposure failed to modify the bronchoconstrictor responses to histamine and methacholine. In contrast, prior challenge with histamine did not modify the subsequent bronchoconstrictor responses to histamine and methacholine in both normal and asthmatic subjects. Pretreatment with ipratropium bromide attenuated the histamine-induced bronchoconstriction, suggesting that airway effects of histamine, in part, are vagally mediated. These data suggest that prior muscarinic stimulation has a protective effect on histamine-induced bronchoconstriction in normal subjects and the absence of this inhibitory effect in asthmatic patients may represent loss of a protective muscarinic receptor mechanism.

Original languageEnglish (US)
Pages (from-to)1285-1291
Number of pages7
Issue number6
StatePublished - Jan 1 1989

ASJC Scopus subject areas

  • Pulmonary and Respiratory Medicine
  • Critical Care and Intensive Care Medicine
  • Cardiology and Cardiovascular Medicine


Dive into the research topics of 'Is there loss of a protective muscarinic receptor mechanism in asthma?'. Together they form a unique fingerprint.

Cite this