Clenbuterol administration does not attenuate the exercise-induced pulmonary arterial, capillary or venous hypertension in strenuously exercising Thoroughbred horses.

The researchers explored whether giving a drug called clenbuterol to race horses could reduce high blood pressure in their lungs during intense exercise and thus lessen the occurrence of exercise-induced pulmonary haemorrhage, a condition where intense exercise can cause bleeding in the horses’ lungs. On testing, they found that the drug did not cause any significant changes in the horses’ blood pressure nor did it reduce the occurrence of the lung condition.

Research Methodology

• The team of researchers conducted thorough experiments on 6 healthy, well-trained Thoroughbred horses.
• They tested each horse under two conditions: the control condition without any medications, and after administering clenbuterol. The order of the conditions was randomised for every horse, and a gap of one week was maintained between these tests.
• The pressure in different parts of the heart and the lung was measured using specialised tools both when the horses were at rest and during strenuous exercise – specifically uphill galloping at a fast pace that resulted in the horses’ heart rate reaching its maximum level and induced exercise-induced pulmonary haemorrhage.

Key Findings

• In the control condition, the intense exercise resulted in a significant increase in pressure in different parts of the right side of the heart and the lungs, and all horses experienced the lung condition.
• Administering clenbuterol while the horses were standing did make their heart beat faster, but it did not lead to any significant changes in the horses’ blood pressure.
• Even during exercise after the drug was administered, the pressure in the heart and lungs still increased with the intensity of the exercise, similar to what was observed in the control condition.
• Crucially, administering clenbuterol did not reduce the occurrence of exercise-induced pulmonary haemorrhage.

Concluding Observations

• Since administering the drug did not affect the pressure across the lung (transpulmonary pressure) during exercise, the researchers infer that it likely does not affect the force exerted on the walls of the lung’s blood vessels.
• Overall, the recommended dosage of clenbuterol does not appear to be effective in reducing the blood pressure in the pulmonary system (lungs) of racing horses or in preventing a lung condition arising from intense exercise.