Both inhaled histamine and hypertonic saline increase airway reactivity innon-sensitised rabbits

Background: Asthmatics react with bronchoconstriction upon a variety of sti muli, i.e. exercise and hypertonic aerosol challenge. We have previously sh own that hy perventilation with dry gas in a rabbit model resulted in a cha nge of the ion content of the tracheal wall. This was followed by a hyperre active response to histamine. Objective: We hypothesised that nebulisation with 3.6% hypertonic saline will be accompanied by a hyperreactive response to histamine in a rabbit model. Methods: Anaesthetised rabbits were given histamine after nebulisation with hypertonic saline. In addition, repeat ne bulisation with hypertonic saline was given with or without histamine betwe en these nebulisations. Results: There was a different response to histamin e 10mg.ml(-1) whether hypertonic saline had been given or not (p < 0.001). Histamine nebulisation, given after hypertonic saline, caused an increase f rom baseline in resistance of 65 +/- 12 cm H2O litre-ls (mean I SEM, p < 0. 001) and a decrease in compliance of 2.3 +/- 0.4 ml cm H2O-1 (P < 0.001). T he corresponding values for the control animals were 10 +/- 0.4 ml. cm H2O litre(-1)s (n.s.) and 1.7 +/- 0.2 ml cm H2O-1 (p < 0.001). At a second nebu lisation with hypertonic saline, with a histamine challenge 30 min before, the resistance increased from baseline by 35 +/- 10 cm H2O litre(-1)s (p < 0.01). This was not observed when no histamine had been given between the h ypertonic saline nebulisations. Conclusions: This study in rabbits shows th at hypertonic solutions cause an increase in the responsiveness to histamin e and that histamine causes an increase in responsiveness to hypertonic sal ine. This is similar to the response of asthmatics to hypertonic saline.