Ureteral ligation prevents the haemodynamic effect of frusemide in pentobarbitol anaesthetised horses.
Authors: Hubbell J A E, Hinchcliff K W, Grosenbaugh D A, Beard W L, Beard L A
Journal: Equine veterinary journal
Summary
# Editorial Summary: Ureteral Ligation Study on Frusemide Haemodynamics Frusemide is widely used in equine practice to reduce pulmonary vascular pressures both at rest and during exercise, yet the precise mechanism behind these beneficial effects remained unclear—specifically, whether the drug's haemodynamic benefits depend on actual fluid loss (diuresis) or operate through other pathways. Hubbell and colleagues investigated this question using 24 anaesthetised horses assigned to four groups: frusemide with normal ureteral function, frusemide with surgically ligated ureters (preventing urine formation), saline placebo with ligated ureters, and frusemide combined with phenylbutazone in ligated-ureter horses. When horses retained normal renal function, frusemide (1 mg/kg IV) significantly reduced mean right atrial, pulmonary artery and aortic pressures whilst increasing plasma total protein concentration, indicating fluid mobilisation; however, when ureteral ligation prevented diuresis, frusemide produced no significant haemodynamic changes, and the addition of phenylbutazone actually reversed this, increasing pressures. These findings definitively demonstrate that frusemide's haemodynamic benefits in horses depend entirely on diuresis and are attributable to reduction in circulating blood volume rather than direct pharmacological effects on the vasculature. For equine practitioners, this underscores that frusemide's efficacy in managing conditions such as exercise-induced pulmonary haemorrhage or pulmonary oedema relies fundamentally on the drug's ability to promote fluid excretion, suggesting that adequate hydration status and renal function are critical prerequisites for therapeutic success.
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Practical Takeaways
- •Frusemide's beneficial effects on pulmonary pressures in horses depend on urine production; any condition that impairs renal function may reduce its therapeutic efficacy
- •Concurrent use of phenylbutazone with frusemide in horses may have adverse haemodynamic effects and should be monitored carefully
- •Understanding that frusemide works through volume reduction rather than direct pressure modulation helps explain variable responses in clinical cases
Key Findings
- •Frusemide reduced mean right atrial, pulmonary artery, and aortic pressures and increased plasma total protein concentration only in horses with intact ureters
- •Frusemide had no significant haemodynamic effect in horses with ligated ureters, demonstrating diuresis is necessary for its haemodynamic benefits
- •Phenylbutazone combined with frusemide in ligated-ureter horses increased mean right atrial, pulmonary artery, and aortic pressures, suggesting interaction between NSAIDs and diuretics
- •The haemodynamic effects of frusemide in horses are attributable to reduction in plasma and blood volume rather than direct cardiovascular effects