Protective effects of inhaled aminophylline on methacholine-induced airway responses in greyhound dogs

Aminopylline can be delivered as a heated aerosol via an air-powered small-volume nebulizer. We tested the hypothesis that inhaled aminophylline could attenuate the effects of inhaled methacholine on the airways. Five greyhound dogs were anesthetized, intubated, and ventilated. An esophageal balloon and flow transducer were placed in the ventilator circuit and connected to a BICORE CP-100 respiratory monitor. We measured mean lung resistance, lung dynamic compliance, and work of breathing. Each dog was pretreated for 30 minutes with three different formulations given randomly on separate days: aerosolized saline and intravenous saline, aerosolized aminophylline and intravenous saline, and aerosolized saline and intravenous aminophylline. The dogs were then exposed to a series of five inhalations of methacholine of increasing concentrations given at 15-minute intervals. The results demonstrated a significant reduction in the work of breathing and lung resistance and significantly increased compliance after treatment with aerosolized aminophylline but not with intravenous aminophylline. These findings support our hypothesis that aerosolized aminophylline has a protective effect against methacholine-induced bronchospasm. The results further suggest the possible use of aerosolized aminophylline for the treatment of obstructive lung disease.