Effect of ascorbic acid on airway responsiveness in ovalbumin sensitized guinea pigs

The most important pathological feature of asthma is airway inflammation, which results in airway hyper-responsiveness. We hypothesized that excessive oxidation is likely to contribute to airway inflammation in asthma. The aim of this study was to evaluate the effects of both acute exposure and a 30-day administration of ascorbic acid (AA), which has an antioxidant effect, on airway responsiveness in sensitized guinea pigs.

Guinea pigs sensitized to ovalbumin (OA), were given drinking water without AA (group 2) or with AA (group 3). The responses of tracheal chains of control animals (group 1) and both groups of sensitized guinea pigs (n = 10, for all groups) to cumulative concentrations of methacholine were measured, and the effective concentrations of methacholine causing 50% of maximum response (EC50 M) were obtained. The response of tracheal chains to 0.1% OA, relative to contraction obtained with 10 micro mol/L methacholine, was also measured. The tracheal responses to methacholine and OA were measured on tissues both incubated and not incubated with AA.

The tracheal responses of group 2 tissues were significantly greater than those of groups 1 and 3 to both OA and methacholine (P < 0.05). There were no significant differences in tracheal responses to OA and methacholine between groups 1 and 3. Acute incubation of tissues caused a reduction of tracheal response to methacholine in all groups, but this was only significantly differ-ent for group 3 (P < 0.05). Acute incubation of tissues did not change tracheal response to OA significantly.

These results showed that although short-term administration of AA had no major effect on tracheal responsiveness among sensitized animals, 30-day administration of AA could lead to a decrease in airway responsiveness of sensitized guinea pigs to both OA and methacholine.