Clenbuterol administration does not attenuate the exercise-induced pulmonary arterial, capillary or venous hypertension in strenuously exercising Thoroughbred horses.
Authors: Manohar M, Goetz T E, Rothenbaum P, Humphrey S
Journal: Equine veterinary journal
Summary
# Editorial Summary: Clenbuterol and Exercise-Induced Pulmonary Hypertension in Thoroughbreds Manohar and colleagues investigated whether clenbuterol, a β₂-adrenergic agonist commonly used in equine practice, could reduce the pulmonary hypertension that occurs during high-intensity exercise and thereby mitigate exercise-induced pulmonary haemorrhage (EIPH). Six conditioned Thoroughbreds underwent maximal exercise testing (14.2 m/s on a 3.5% uphill grade) under both control and clenbuterol-treated conditions (0.8 µg/kg i.v.), with right heart and pulmonary vascular pressures measured via catheter-tip transducers at rest, submaximal, and maximal workloads. Whilst clenbuterol produced tachycardia at rest, it failed to reduce right atrial, pulmonary arterial, capillary, or wedge pressures during exercise compared to control conditions, and EIPH continued to occur in all horses regardless of treatment. The findings suggest that clenbuterol does not alter the transmural pressure gradient across the pulmonary blood–gas barrier during exercise at the recommended clinical dosage. For practitioners managing EIPH, these results indicate that β₂-adrenergic stimulation is unlikely to be an effective strategy for reducing exercise-induced pulmonary hypertension, and alternative management approaches targeting the pathophysiology of EIPH remain necessary.
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Practical Takeaways
- •Beta2-adrenergic stimulation with clenbuterol is ineffective for preventing or reducing exercise-induced pulmonary hemorrhage in performance horses, despite theoretical benefits.
- •Clenbuterol should not be relied upon as a preventive strategy for EIPH in Thoroughbreds or similar high-performance horses undergoing strenuous training.
- •Alternative management or pharmacological approaches should be investigated for horses prone to EIPH, as this commonly used medication does not address the underlying pulmonary vascular pressure dynamics.
Key Findings
- •Clenbuterol administration caused tachycardia at rest but did not significantly alter right atrial or pulmonary vascular pressures in standing horses.
- •During high-intensity exercise (14.2 m/s uphill gallop), clenbuterol did not attenuate the progressive increases in pulmonary arterial, capillary, or wedge pressures compared to control conditions.
- •All 6 horses experienced EIPH during maximal exercise in both control and clenbuterol treatment conditions, with incidence remaining unaffected by drug administration.
- •Clenbuterol did not alter transpulmonary pressure during exercise, suggesting it does not reduce transmural force on the blood-gas barrier at recommended dosages.