Stretch-induced myogenic responses of airways after histamine and carbachol

The purpose of the study described here was to determine the possible role of a myogenic response of bronchial smooth muscle in deep inspiration (DI)-induced bronchoconstriction. Model experiments were performed on sheep tracheal strips. The effect of sudden stepwise elongation on isometric tension of tracheal muscle was studied in the absence and presence of the bronchoconstrictors carbachol (10(-8) M) and histamine (10(-4) M). In control strips tension increased rapidly with stretch and was followed by stress relaxation which corresponds to creep or bronchial dilatation. In histamine- and carbachol-treated strips a reactive contraction with a rhythmic pattern interrupted the process of stress relaxation. These responses appeared after only 20% elongation and were characteristic of a myogenic contraction which in the in vivo situation would correspond to a bronchoconstriction. These findings are interpreted as a functional transformation of multiple- to single-unit smooth muscle due to the influence of carbachol and histamine. This suggests that stretching (DI) of bronchial smooth muscle in the presence of carbachol and histamine induces a protracted myogenic contraction, which may explain bronchoconstriction after DI in severe asthma.