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Related Experiment Videos

Methacholine causes reflex bronchoconstriction

E M Wagner1, D B Jacoby

  • 1Divisions of Pulmonary and Critical Care Medicine and of Physiology, The Johns Hopkins University, Baltimore, Maryland 21224, USA. wagnerem@welchlink.welch.jhu.edu

Journal of Applied Physiology (Bethesda, Md. : 1985)
|January 14, 1999
PubMed
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Methacholine causes reflex airway smooth muscle constriction, mediated by the vagus nerve. This challenges the assumption that methacholine responses solely reflect direct smooth muscle effects.

Area of Science:

  • Pulmonary Physiology
  • Respiratory Medicine

Background:

  • Methacholine is commonly used to assess airway hyperresponsiveness.
  • Its effects are often assumed to be direct on airway smooth muscle.

Purpose of the Study:

  • To investigate if methacholine induces vagally mediated reflex bronchoconstriction.
  • To differentiate direct vs. reflex effects of methacholine on airway smooth muscle.

Main Methods:

  • Methacholine was administered to sheep via bronchial artery or aerosol.
  • Trachealis smooth muscle contraction and airway resistance were measured.
  • The impact of bilateral vagotomy on these responses was assessed.

Main Results:

  • Bronchial artery and aerosolized methacholine caused dose-dependent trachealis contraction and increased airway resistance.

Related Experiment Videos

  • Bilateral vagotomy significantly attenuated these methacholine-induced responses.
  • Trachealis smooth muscle tension increased by 186% and airway resistance by 183% with highest methacholine dose.

    • Conclusions:

    • Methacholine induces significant reflex contraction of airway smooth muscle.
    • The assumption that methacholine responses are solely direct effects on smooth muscle may be invalid.