Influence of furosemide on hemodynamic responses during exercise in horses.

This study explored the effects of furosemide, at varying doses, on the hemodynamic responses of exercising horses. The drug was found to influence cardiovascular parameters such as resting right atrial pressure, carotid arterial pressure, and pulmonary arterial pressure, both at rest and during exercise, but not heart rate or lactate concentration. The furosemide effects were found to not be solely due to its diuretic properties.

Hemodynamic Measurements

• The researchers measured parameters such as carotid arterial pressure (CAP), pulmonary arterial pressure (PAP), and heart rate in horses both at rest and during high-speed treadmill exercise.
• These measurements were consistent at rest between the initial and four hours post-administration of furosemide. However, after high doses of furosemide, there were observable changes in resting right atrial pressure (RAP), with a reduction noticed four hours post-injection.

Furosemide Effects

• During exercise, as treadmill speed increased, so did RAP, CAP, PAP, and heart rate, indicating a clear correlation between physical exertion and these cardiovascular parameters.
• When furosemide was administered before exercise, both RAP and PAP decreased during exercise, with the effect being dose-dependent. However, heart rate remained unchanged.
• At the high dosage of 2 mg/kg, the drug significantly reduced the mean CAP during exercise at speeds of 9 and 11 m/s, but this effect was not observed at a treadmill speed of 13 m/s.

Post-Exercise and Recovery

• After the exercise, only RAP levels decreased with furosemide administration.
• The plasma lactate concentration, a measure often used to assess the intensity of exercise, remained unaffected by the introduction of the drug.

Other Observations

• While there were no observed changes in packed cell volume (PCV) or hemoglobin concentration at rest prior to exercise, these variables did increase in a dose-dependent manner during exercise and recovery after furosemide was administered.
• The changes in PCV and hemoglobin, however, were relatively small compared to the alterations in RAP and PAP, suggesting that the effects of furosemide extend beyond its diuretic capabilities.

Interpretation and Implications

• Furosemide may exercise its effects on the cardiovascular system, not just through promoting urination (diuresis), but potentially through vasodilatory activities as well. These activities could lower pulmonary arterial pressure directly whilst also enlarging venous capacity, therefore reducing venous return to the atria and cardiac filling.