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

Abstract

Abstract Objectives To determine whether IV administration of furosemide (250 mg) to horses before maximal exercise affected maximal oxygen consumption (V⃙o2max), breathing mechanics, or gas exchange during exercise. Animals 7 healthy, well-conditioned Thoroughbred horses. Procedures 5 horses initially performed an incremental treadmill exercise test to determine V⃙o2max 4 hours after IV administration of furosemide (250 mg IV) or placebo (saline [0.9% NaCl] solution). Time to fatigue and distance run were recorded. All 7 horses were then used to determine the effects of furosemide on gas exchange and breathing mechanics at 40, 60, 80, and 100% of V⃙o2max. Horses were weighed immediately before exercise. Results Furosemide treatment significantly increased mass-specific V⃙o2max (5.3%), but absolute V⃙o2max was not significantly altered. In the 2 parts of the study, body weights were 2.9 and 2.5% higher when horses were given placebo than when they were given furosemide. Time and distance run at speeds ≥ 11.0 m/s were significantly greater following furosemide administration. Furosemide treatment had no effect on breathing mechanics or gas exchange. Conclusions and Clinical Relevance Previous studies have suggested that prerace 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 V⃙o2max but not to improvements in breathing mechanics or gas exchange. Most of the increase in mass-specific V⃙o2max appeared to be attributable to weight loss associated with diuresis induced by furosemide. (Am J Vet Res 1999;60:1415–1422)