Effects of exercise, furosemide, blood depletion, and reinfusion on body fluid compartment volumes in horses

High pulmonary blood pressure contributes to exercise-induced pulmonary hemorrhage. The objective of this study was to use bioimpedance spectroscopy to assess body fluid compartment volumes under 3 conditions in 6 racehorses: i) Pre- and post-supramaximal treadmill exercise (control); ii) Exercise 4 hours after furosemide (0.5 mg/kg body weight, IV); iii) Exercise, removal of ~14 L of blood and subsequent reinfusion of the blood. Statistical analysis used linear mixed effects models. Body compartment volumes did not change during the control runs. Total body water (TBW) ( = 0.007, = 0.007), extracellular fluid (ECF) ( = 0.003, = 0.003), and intracellular fluid (ICF) volumes ( = 0.04, = 0.04) decreased pre- and post-exercise following furosemide administration. The ICF trended to decrease ( = 0.07) after slow removal of blood. Blood reinfusion increased TBW ( = 0.02, = 0.02) and ICF ( = 0.005, = 0.005) pre- and post-exercise.