Effect of intravenous administration of furosemide on mass-specific maximal oxygen consumption and breathing mechanics in exercising horses

Objectives-To determine whether IV administration of furosemide (250 mg) to horses before maximal exercise affected maximal oxygen consumption ((V) ov er dot O-2 max), breathing mechanics, or gas exchange during exercise. Animals-7 healthy, well-conditioned Thoroughbred horses. Procedures-5 horses initially performed an incremental treadmill exercise t est to determine (V) over dot O-2 max 4 hours after IV administration of fu rosemide (250 mg IV) or placebo (saline [0.9% NaCl] solution). Time to fati gue and distance run were recorded, Ail 7 horses were then used to determin e the effects of furosemide on gas exchange acid breathing mechanics at 40, 60, 80, and 100% of (V) over dot O-2 max. Horses were weighed immediately before exercise, Results-Furosemide treatment significantly increased mass-specific (V) over dot O-2 max (5.3%), but absolute (V) over dot O-2 max was not significantl y altered, In the 2 parts of the study, body weights were 2.9 and 2.5% high er when horses were given placebo than when they were given furosemide. Tim e and distance run at speeds greater than or equal to 11.0 m/s were signifi cantly greater following furosemide administration. Furosemide treatment ha d no effect on breathing mechanics or gas exchange, Conclusions and Clinical Relevance-Previous studies have suggested that pre race administration of furosemide may have a positive effect on performance , Results of this study indicate that this may be attributable, in part, to an increase in mass-specific (V) over dot O-2 max but not to improvements in breathing mechanics or gas exchange. Most of the increase in mass-specif ic (V) over dot O-2 max appeared to be attributable to weight loss associat ed with diuresis induced by furosemide.