Effects of length oscillation on the subsequent force development in swinetracheal smooth muscle

It has been shown that deep inspiration (DI) taken before application of br onchoconstricting stimuli causes a reduction in the subsequent bronchoconst riction; a fast DI has a greater inhibitory effect than a slow DI. We hypot hesize that periodic length changes imposed on a relaxed airway smooth musc le (ASM) would attenuate subsequent bronchoconstriction by disrupting the o rganization of the contractile apparatus, and this could be an important me chanism for the observed bronchoprotective effect of DI and tidal breathing . Length oscillations of different amplitude, frequency and duration were a pplied to a relaxed muscle. The effects of such perturbations on force deve lopment were then assessed. Results show that oscillations reduce the subse quent force generation and that the magnitude of force reduction is proport ional to amplitude and duration of the length oscillation. After the oscill ation, isometric force recovered to the preoscillation level in a series of isometric contractions, and the rate of recovery was facilitated by freque nt stimulation. The in vitro behavior of ASM found in this study could acco unt for the observed temporary reduction in bronchoconstriction subsequent to a DI.