Airway responsiveness to adenosine 5' monophosphate following inhalation of hypertonic saline

We wished to determine whether the refractory period after hypertonic saline (HS) challenge is due to mast cell mediator depletion. Therefore, the airway responsiveness to adenosine 5' monophosphate (AMP), which induces bronchoconstriction via mast cell histamine release, was determined after the inhalation of HS aerosol. Nine asthmatic subjects attended the laboratory on three occasions. On day 1 HS challenge was performed followed one hour later by a second HS challenge. On day 2 an AMP challenge was performed. On day 3 an HS challenge was performed followed one hour later by an AMP challenge. Airway responsiveness (PD35 sGaw) to an initial HS challenge ranged from 12 to 315 l of aerosol (mean 47 l). Airway responsiveness to a second HS challenge ranged from 8 to 800 l (mean 102 l p = 0.035, n = 9). Airway responsiveness to AMP increased from 0.44 to 14.0 mumol (mean 2.37 mumol) at baseline to 0.3 to 15.5 (mean 1.3 mumol) (p = 0.05) after HS challenge. There was a linear correlation between baseline AMP responsiveness and baseline HS responsiveness (r = 0.911, p = 0.001). There was no correlation between the degree of refractoriness and the change in AMP responsiveness (r = 0.1, p = 0.9). Thus airway responsiveness to AMP increased significantly after inhalation of HS aerosol and this increase was independent of refractory behaviour. Our results suggest that the refractory period to HS is not due to mediator depletion.