Lack of vagal influence on pulmonary visco-elasticity in puppies

We recently demonstrated that most of the change in lung function following inhaled histamine in 8-10 week old puppies was due to changes in the tissue visco-elastic properties and argued that vagally-mediated reflexes may be responsible for this phenomenon (Sly and Lanteri, J. Appl. Physiol. 1990; 68: 1562-1567). To test this hypothesis we compared 5 puppies treated with inhaled lignocaine prior to histamine challenge and 5 puppies with bilateral cervical vagotomy prior to histamine challenge with 5 control animals, not pre-treated priot to histamine challenge. Treatment with inhaled lignocaine or bilateral cervical vagotomy did not alter baseline pulmonary mechanics and there were no differences in the response to histamine challenge between the three groups. These results show that vagal reflexes, mediated via the central nervous system, are not involved in the response of the pulmonary tissues to inhaled histamine, but do not exclude the possible involvement of local axonal reflexes