Responsiveness of isolated tracheal smooth muscle in a canine model of asthma.

Abstract

Mongrel dogs were exposed to aerosols ofAscaris suum antigen and classified as aerosol antigen reactive or nonreactive on the basis of pulmonary resistance changes. Two weeks later the same dogs were anesthetized and strips of canine trachealis airway smooth muscle were prepared for in vitro studies. Low concentrations of methacholine caused significantly stronger isometric contractions of strips from aerosol reactive animals than of control strips. Contractile responses to maximal concentrations of methacholine were identical in both groups. Strips were precontracted with a half-maximal effective concentration of methacholine. Cumulative isoproterenol concentration-response curves were then run and strips from control dogs relaxed to a significantly greater degree than those from aerosol reactive dogs. The results indicate that the in vitro pharmacological responsiveness of the trachealis muscle can be correlated with the in vivo responsiveness of these animals to Ascaris suum aerosol bronchial provocation.