Effect of inhaled substance P and neurokinin A on the airways of normal and asthmatic subjects.

Abstract
The neuropeptides substance P and neurokinin A are present in sensory airway nerves. Their effect on airway calibre was compared in six healthy non-smoking subjects and six asthmatic subjects. On separate days increasing concentrations (from 10-9 to 10-6 mol/ml) of each neuropeptide were administered by nebuliser and the airway response measured as charge in specific airway conductance (sGaw). Substance P and neurokinin A caused no change in sGaw in the healthy subjects. Inhalation of substances P up to the highest concentration of 10-6 mol/ml caused no change in sGaw in the asthmatic subjects. Neurokinin A, however, caused bronchoconstriction with a mean fall in sGaw of 48% (SEM 12%) after 5 .times. 10-7 mol/ml. The onset of bronchonconstriction was rapid, but sGaw had returned to baseline values within one hour in all but one patient.