FUROSEMIDE REDUCES ACCUMULATED OXYGEN DEFICIT IN HORSES DURING BRIEF INTENSE EXERTION

We theorized that furosemide-induced weight reduction would reduce the contribution of anaerobic metabolism to energy expenditure of horses during intense exertion. The effects of furosemide on accumulated O-2 deficit and plasma lactate concentration of horses during high-intensi ty exercise were examined in a three-way balance randomized crossover study. Nine horses completed each of three trials: 1) a control (C) tr ial, 2) a furosemide-unloaded (FU) trial in which the horse received f urosemide 4 h before running, and 3) a furosemide weight-loaded (FL) t rial during which the horse received furosemide and carried weight equ al to the weight lost-after furosemide administration. Horses ran for 2 min at similar to 120% maximal O-2 consumption. Furosemide (FU) incr eased Og consumption (ml . 2 min(-1). kg(-1)) compared with C (268 +/- 9 and 257 +/- 9, P < 0.05), whereas FL was not different from C (252 +/- 8). Accumulated O-2 deficit (ml O-2 equivalents/kg) was significan tly (P < 0.05) lower during FU (81.2 +/- 12.5), but not during FL (96. 9 +/- 12.4), than during C (91.4 +/- 11.5). Rate of increase in blood lactate concentration (mmol . 2 min(-1). kg(-1)) after FU (0.058 +/- 0 .001), but not after FL (0.061 +/- 0.001), was significantly (P < 0.05 ) lower than after C (0.061 +/- 0.001). Furosemide decreased the accum ulated Oz deficit and rate of increase in blood lactate concentration of horses during brief high-intensity exertion. The reduction in accum ulated O-2 deficit in FU-treated horses was attributable to an increas e in the mass-specific rate of O-2 consumption during the high-intensi ty exercise test.