Effects of dystrophy and age on hamster tracheal smooth muscle function

Pharmacological and morphometric evaluations of airway smooth muscle were performed on tracheal segments from control and dystrophic hamsters at 50, 145 and 315 days of age. An age-related change in muscle volume index (a measure of the total smooth muscle per tracheal segment) was not observed in the control group but decreased with age in the dystrophic strain. In the control strain, correlations were not observed between age and maximum pharmacological response to the drugs tested, but a change in sensitivity to carbachol and KCl was noted at 145 days. In contrast, tracheal segments of dystrophic hamsters exhibited decreased maximum responses to carbachol, KCl, histamine, and isoproterenol at 315 days of age. When maximal contractile responses were normalized by muscle volume index, only the KCl maximum tension at 315 days was less than at 50 days of age. Changes in sensitivity to carbachol and KCl were also seen in tracheal smooth muscle of the dystrophic hamster at 145 days of age. At 315 days, histamine and isoproterenol-induced relaxation was less in dystrophic than in control tracheal smooth muscle. It is not possible to ascertain whether the decreased responses of the tracheal segments from the oldest dystrophic hamsters are due to dystrophy alone, or to a combination of dystrophy and aging.