Corticosteroids decrease airway hyperresponsiveness in the Basenji-Greyhound dog model of asthma

Methacholine and citric acid responses were assessed before, during, and after 6 wk of oral treatment with either placebo or methylprednisolone (2 mg.kg-1.day-1) in 12 Basenji-Greyhound dogs. Bronchoalveolar lavage was performed in three dogs in each group before, during, and after pretreatment. Base-line airway resistance and dynamic compliance did not change with treatment in any of the groups. Placebo treatment had no demonstrable effect on methacholine and citric acid responsiveness. Methylprednisolone treatment abolished the constrictor response to citric acid during the 4th and 6th wk of treatment and significantly reduced methacholine responsiveness during the 3rd and 5th wk of treatment. Methylprednisolone treatment was associated with a marked reduction in the percent of eosinophils, but not mast cells, in the bronchoalveolar lavage fluid during the 7th wk. Blood eosinophil counts were also markedly reduced in the methylprednisolone-treated group compared with the placebo-treated group during the 7th wk. The decrease in numbers of eosinophils in blood and bronchoalveolar lavage fluid suggests interference with the inflammatory process as a possible mechanism for the observed reduction in airway hyperresponsiveness in the Basenji-Greyhound dog.