Canine pulmonary response to aerosol histamine: direct versus vagal effects

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Abstract
Histamine was previously shown to produce bronchoconstriction both directly and by a vagal reflex. The pulmonary response of dogs exposed to increasing doses of aerosol histamine before and after vagal blockade or vagotomy was studied. The relative contributions of aerodynamically large and small airways to overall response were determined by measurement of pulmonary resistance on sulfur hexafluoride-O2 and He-O2 mixtures. Histamine aerosol caused a similar dose-dependent increase in resistance of aerodynamically large and small airways and fall in dynamic compliance. The dose-response relationships were not consistently altered by vagal blockade or vagotomy. The following variables did not apparently alter the results: anesthesia, type of aerosol generator, control of breathing during aerosol exposure, spontaneous breathing vs. controlled ventilation after aerosol exposure and cold block of vagi vs. vagotomy. Histamine aerosol in dogs apparently caused a local dose-dependent constriction of bronchial smooth muscle, and the vagus nerve played a relatively minor role in the pulmonary response to aerosol histamine in these experiments.