Methacholine hyperresponsiveness in mice with house dust mite-induced lung inflammation is not associated with excessive airway constriction ex vivo.

The role of excessive airway constriction in the hyperresponsiveness to nebulized methacholine in mice with experimental asthma is still contentious. Yet, there have been very few studies investigating whether the increased in vivo response to methacholine caused by experimental asthma is associated with a corresponding increase in ex vivo airway constriction. Herein, the responses to nebulized methacholine in vivo and airway constriction in lung slices ex vivo were studied in 8- to 10-week-old male mice of two strains, BALB/c and C57BL/6. Experimental asthma was induced by administering house dust mites (HDM) intranasally, once daily, for 10 consecutive days. Complementary ex vivo studies were conducted with excised tracheas to measure and compare isometric force. As expected, the in vivo response to methacholine, and especially the hyperresponsiveness caused by HDM, was greater in BALB/c than in C57BL/6 mice. In contrast, there were no differences in maximal airway constriction between mouse strains, and the hyperresponsiveness to nebulized methacholine caused by HDM in both mouse strains was not associated with a corresponding increase in ex vivo airway constriction. The experiments with excised tracheas demonstrated no differences in isometric force between strains and between mice with and without experimental asthma. It is concluded that the hyperresponsiveness to nebulized methacholine in an acute mouse model of asthma induced by repeated HDM exposures is not associated with excessive airway constriction ex vivo.