Effect of furosemide on physiologic variables in exercising horses.

The study explores the impact of furosemide, a type of diuretic, on certain physiological variables in horses during exercise. It found that furosemide raises pH levels in the blood, likely affects oxygen uptake in exercising muscles, and has various impacts depending on the breed of the horse.

Research Objective and Methodology

• The purpose of this research was to examine the effects of furosemide, a medication often used in racehorses to prevent pulmonary bleeding, on the physiological variables in horses during exercise.
• The study involved twelve horses (6 Standardbreds and 6 Thoroughbreds), which received intramuscular injections of either 250 mg of furosemide or a physiologic saline solution.
• Subsequently, the horses underwent standardized exercise tests. The researchers measured blood gas values, packed cell volume (PCV), plasma lactile concentration, and heart rate during these exercises.

Key Findings

• Administering furosemide caused a significant increase in both arterial and venous blood pH values. An increase in pH signifies more alkali (less acidic) blood conditions.
• The partial pressures of oxygen (O2) and carbon dioxide (CO2) in arterial blood, and the CO2 levels in venous blood, remained unaffected by the furosemide treatment. These readings indicate the gas exchange efficiency of the respiratory system.
• However, during exercise, the venous partial pressures of oxygen were significantly less after the furosemide treatment. The researchers suggest this could indicate an increase in oxygen uptake by the exercising muscles or a change in cardiac output.

Breed Specific Effects

• The research also revealed a significant difference between Thoroughbred and Standardbred horses in terms of arterial and venous pH, PaO2, PaCO2, plasma lactate concentration, and heart rate.
• This means the impact of the drug and the body’s physiological response to exercise might vary between horse breeds. In particular, the findings suggest that Standardbreds exercised at a relatively higher work rate than Thoroughbreds.