Effect of furosemide and the equine nasal strip on exercise-induced pulmonary haemorrhage and time-to-fatigue in maximally exercising horses

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Furosemide (FUR) and the equine nasal strip (NS) decrease exercise-induced pulmonary haemorrhage (EIPH) compared with control (CON) conditions in the Thoroughbred horse during near-maximal running trials. As FUR and NS have potential performance-enhancing properties, we studied Thoroughbreds running to fatigue to test the hypothesis that time-to-fatigue (TTF) would be increased, yet EIPH reduced, in FUR and NS compared with CON. Thoroughbred geldings (n = 6) were run to volitional fatigue on a level treadmill (1 m s−1 increment per minute from an initial trot) every two weeks (order randomized) under CON, NS, FUR (1 mg kg−1; 4 h prior) and FUR+NS conditions. Pulmonary arterial pressure (Ppa) and pulmonary gas exchange were measured throughout exercise, while arterial blood gases were sampled at the end of each 1-min stage. EIPH severity was quantified via bronchoalveolar lavage (BAL) at 30 min post-exercise. TTF was increased for all experimental conditions (i.e. an additional 20±13, 28±8 and 40±6 s for NS, FUR and FUR+NS, respectively; P < 0.05) compared with CON. Peak mean Ppa was significantly reduced (P < 0.05) for FUR (93.6±6.3 mmHg) and FUR+NS (95.4±5.1 mmHg), yet unchanged with NS (98.0±5.8 mmHg; P > 0.05) compared with CON (100.5±4.9 mmHg). All three experimental conditions exhibited a significant reduction in EIPH compared with CON (64.1±36.8× 6 red blood cells (RBCs) ml−1); however, no significant difference was noted between these conditions (×106 RBCs ml−1: 29.1±16.8, 20.9±13.1 and 26.7±19.8 for NS, FUR and FUR+NS, respectively). Furthermore, no differences for either end-exercise cardiorespiratory (i.e. V˙O2 or V˙CO2) or blood-borne metabolic (i.e. blood gases, lactate or pH) variables were observed. These findings demonstrate that both FUR and NS enhance TTF and reduce EIPH to a similar degree during high-speed treadmill running to fatigue.

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