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

The researchers undertook a study to determine if furosemide, a diuretic often used to treat horses, affected the properties of blood flow, along with serum and red blood cell (RBC) electrolyte concentrations in thoroughbreds during submaximal treadmill exercise. The findings suggest that any beneficial effects of furosemide in reducing the severity of exercise-induced pulmonary hemorrhage in horses cannot be explained by improved blood flow properties.

Research Methodology

• The researchers selected five healthy thoroughbreds who had raced within the past year, but showed no history of exercise-induced pulmonary hemorrhage.
• The horses were then subjected to submaximal treadmill exercise, a level of exercise that was less than their maximum effort, both with and without treatment of furosemide.
• The dose of furosemide given was 1mg per kg of body weight, and was administered intravenously.
• Blood samples were taken at various intervals: before exercise, at treadmill speeds of 9 and 13 m/s, and ten minutes after exercise. The researchers then determined the results of hemorheologic (the study of blood flow) and electrolyte tests.

Research Findings

• The administration of furosemide led to a range of hemorheologic changes. 60 minutes after administration, there was an increase in PCV, plasma total protein concentration, whole blood viscosity, mean RBC volume, and RBC potassium concentration. There were also decreases in serum potassium concentration, serum chloride concentration, and RBC chloride concentration.
• Furosemide treatment also had an effect on changes associated with exercise. It attenuated the exercise-associated changes in RBC size, serum sodium concentration, serum potassium concentration, RBC potassium and chloride concentrations, and RBC density.
• The treatment also exacerbated exercise-associated increases in whole blood viscosity.
• However, the treatment did not have any effect on RBC filterability (the rate and ease with which red blood cells pass through small capillaries).

Conclusions

• Overall, the authors concluded that the hemorheologic effects of furosemide were likely due to changes in total body fluid and electrolyte balance and changes across the membrane of the red blood cells. These would not improve the properties of blood flow.
• 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.