Effects of furosemide on hemorheologic alterations induced by incremental treadmill exercise in thoroughbreds.

OBJECTIVE

To determine whether furosemide treatment altered the blood flow properties and serum and RBC electrolyte concentrations of Thoroughbreds during submaximal treadmill exercise.

DESIGN

Thoroughbreds were subjected to submaximal treadmill exercise with and without treatment with furosemide (1 mg/kg of body weight, IV).

ANIMALS

5 healthy Throughbreds that had raced within the past year and had no history of exercise-induced pulmonary hemorrhage.

PROCEDURE

Venous blood samples were obtained before exercise, at treadmill speeds of 9 and 13 m/s, and 10 minutes after exercise, and hemorheologic and electrolyte test results were determined.

RESULTS

Hemorheologic changes 60 minutes after furosemide administration included increased PCV, plasma total protein concentration, whole blood viscosity, mean RBC volume, and RBC potassium concentration, and decreased serum potassium concentration, serum chloride concentration, and RBC chloride concentration. Furosemide treatment attenuated the exercise-associated changes in RBC size, serum sodium concentration, serum potassium concentration, RBC potassium and chloride concentrations, and RBC density; exacerbated exercise-associated increases in whole blood viscosity; and had no effect on RBC filterability.

CONCLUSIONS

The hemorheologic effects of furosemide probably occurred secondary to total body and transmembrane fluid and electrolyte fluxes and would not improve blood flow properties.

CLINICAL RELEVANCE

The beneficial effects of furosemide treatment in reducing the severity of bleeding in horses with exercise-induced pulmonary hemorrhage cannot be explained by improved blood flow properties.