Morphologic changes in the airways induced by recurrent exposure of acetylcholine in the guinea pig

The morphologic changes in peripheral airways of guinea pigs derived from asthmalike breathing induced by acetylcholine (Ach) exposure were studied. In the Ach-exposed animals, the smooth muscle in the respiratory units (alveolar mouth of the alveolar duct) as well as in the peripheral airways was increased. The internal and external diameters of the peripheral airways were not significantly different between Ach-exposed and control animals. In addition, the Ach-exposed animals had higher specific diaphragm weights (diaphragm to body weight). We conclude that recurrent asthmalike breathing brings about increased smooth muscle, but the increased muscle contributes little to airway dimensions. We speculate that an increased airway wall thickness inside the outermost layer of smooth muscle may play a role in increasing airway reactivity.