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The effect of sildenafil citrate administration on selected physiological parameters of exercising Thoroughbred
P T Colahan1, C A Jackson, B Rice
1Equine Performance Laboratory, College of Veterinary Medicine, University of Florida, Gainesville, USA. colahanp@vetmed.ufl.edu
Insights
Sildenafil did not improve exercise performance or reduce pulmonary hemorrhage in horses. However, it did alter heart rate responses during intense exercise and recovery.
Area of Science:
- Equine Exercise Physiology
- Pharmacology in Animal Sports
Background:
- Sildenafil, a phosphodiesterase-5 inhibitor, is known to reduce pulmonary arterial pressure (PAP).
- Its potential to enhance athletic performance and prevent exercise-induced pulmonary hemorrhage (EIPH) in horses was investigated.
Purpose of the Study:
- To evaluate the effects of sildenafil citrate on performance metrics in horses.
- To determine if sildenafil reduces exercise-induced pulmonary hemorrhage (EIPH) in equine athletes.
Main Methods:
- A crossover study involving 13 Thoroughbred horses administered sildenafil citrate or placebo.
- Exercise tests included a step-wise test to exhaustion and a 13 m/s test to exhaustion.
- Measurements included gas exchange, lactate, heart rate, runtime, bronchoalveolar lavage (BAL) cytology, and pulmonary arterial pressure (PAP).
Main Results:
- Sildenafil did not significantly alter performance indicators like runtime or reduce EIPH.
- Pulmonary arterial pressure (PAP) was not affected by sildenafil administration.
- Heart rates were significantly altered at submaximal speeds and during recovery post-exercise.
Conclusions:
- Sildenafil citrate did not demonstrate efficacy in improving exercise performance or preventing EIPH in horses.
- The drug modulated cardiovascular responses to exercise, specifically heart rate, but this did not translate to enhanced performance outcomes.
Reasons For Performing Study:
Sildenafil, a phosphodiesterase-5 inhibitor vasodilator, increases cGMP concentrations by inhibiting enzymatic degradation. Marketed to treat erectile dysfunction in men, it also reduces pulmonary arterial pressure (PAP). Because it reduces PAP, sildenafil may enhance performance and/or prevent exercise induced-pulmonary haemorrhage (EIPH).
Objective:
To determine if sildenafil citrate administration altered commonly measured indices of performance or reduced EIPH in exercised horses.
Methods:
Thirteen athletically conditioned Thoroughbred horses (2 mares and 11 geldings, age 3-12 years) were administered sildenafil citrate or placebo in 2 crossover design exercise testing studies. In a step-wise test to exhaustion, inspired/expired gas analysis, blood lactate, heart rate, runtime and bronchoalveolar lavage (BAL) cytology were measured. In a 13 m/s test to exhaustion, blood lactate, heart rate, runtime, BAL cytology and pulmonary arterial pressure were measured. Data were analysed with paired and unpaired t tests, one-way ANOVA and Tukey's pair-wise multiple comparison and Friedman repeated measure analysis of variance on ranks.
Results:
The administration of sildenafil did not alter mean inspired/expired gas measurements, plasma lactate concentrations or acute pulmonary haemorrhage in either exercise test or pulmonary arterial pressure measurement in the 13 m/s trial. Heart rates in both stress tests were significantly different at submaximal speeds and during the early recovery period. Run time was not affected by sildenafil administration in the step-wise trial (P = 0.622) or in the 13 m/s trial (P = 0.059).
Conclusions:
Sildenafil did not alleviate pulmonary haemorrhage or enhance performance-related indices in these trials. Sildenafil administration altered cardiovascular adaptation to intense exercise as evidenced by altered heart rates at submaximal speeds and post exercise. The effect of these alterations on other performance perimeters was not evident.
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