Study objective: We measured tracheal mucus velocity (TMV), a marker of mucociliary clearance (MCC), in sheep before and for 12 h after treatment with salmeterol, albuterol, ipratropium, or vehicle to determine the effects on normal MCC. We also determined if these agents could reverse the depression in TMV caused by inhaled human neutrophil elastase (HNE), a model of abnormal MCC.
Methods: Study 1: TMV was measured initially and then for 6 h after metered-dose inhaler treatment with salmeterol (42 microg), albuterol (180 microg), ipratropium bromide (36 microg), or vehicle. After 6 h, the sheep in the albuterol and ipratropium treatment arms were administered a second dose of drug, whereas the salmeterol and vehicle treatment arms received vehicle. TMV was measured for another 6 h. Study 2: Six sheep inhaled HNE aerosol, which significantly reduced TMV by 2 h. At this point, the sheep were treated with either salmeterol, albuterol, ipratropium, or vehicle, and the effects on TMV were measured for another 6 h. This experiment was repeated in four sheep using only salmeterol and albuterol, but the posttreatment measurements were extended to 12 h.
Results: Study 1: Only salmeterol and albuterol increased TMV (p < 0.05) during the initial 6-h period. From 6 to 12 h only, the salmeterol-treated sheep had TMV that remained at or above the initial TMV for the entire time, although both albuterol and ipratropium showed enhancement of TMV compared to vehicle. Study 2: Salmeterol and albuterol reversed the HNE-induced depression in TMV to a similar degree over the 6-h time course. However, the protection afforded by salmeterol was more prolonged than that seen with albuterol if the posttreatment interval was extended to 12 h. Ipratropium and vehicle had no effect.
Conclusion: We conclude that salmeterol and albuterol can stimulate normal MCC and reverse HNE-induced mucociliary dysfunction and that salmeterol has a longer duration of action in these models of normal and abnormal MCC.