Effect of Clenbuterol on Tracheal Mucociliary Transport in Horses Undergoing Simulated Long-Distance Transportation

BackgroundPneumonia is observed in horses after long-distance transportation in association with confinement of head position leading to reduction in tracheal mucociliary clearance rate (TMCR). Hypothesis/ObjectivesClenbuterol, a beta-2 agonist shown to increase TMCR in the horse, will ameliorate the effects of a fixed elevated head position on large airway contamination and inflammation in a model of long-distance transportation model. AnimalsSix adult horses. MethodsA cross-over designed prospective study. Horses were maintained with a fixed elevated head position for 48hours to simulate long-distance transport, and treated with clenbuterol (0.8g/kg PO q12h) or a placebo starting 12hours before simulated transportation. TMCR was measured using a charcoal clearance technique. Data were collected at baseline and 48hours, and included TMCR, tracheal wash cytology and quantitative culture, rectal temperature, CBC, fibrinogen, and serum TNF, IL-10, and IL-2 levels. There was a 18-21day washout between study arms, and data were analyzed using regression analysis and Wilcoxon rank-sum tests. ResultsTracheal mucociliary clearance rate was significantly decreased after transportation in both treatment (P=.002) and placebo (P=.03) groups. There was a significant effect of treatment on TMCR, with the treatment group showing half the reduction in TMCR compared with the placebo group (P=.002). Other significant differences between before- and after-transportation samples occurred for serum fibrinogen, peripheral eosinophil count, quantitative culture, tracheal bacteria, and degenerate neutrophils, though no treatment effect was found. Conclusions and Clinical ImportanceTreatment with clenbuterol modestly attenuates the deleterious effects of this long-distance transportation model on tracheal mucociliary clearance.