Clenbuterol plasma concentrations after repeated oral administration and its effects on cardio-respiratory and blood lactate responses to exercise in healthy Standardbred horses.

The research finds that the drug clenbuterol does not significantly alter cardio-respiratory or blood lactate parameters in healthy Standardbred horses after submaximal exercise.

Objective of the Study

• The study was designed to investigate the effects of clenbuterol, a beta 2-adrenergic agonist, on the cardio-respiratory parameters and blood lactate levels in relation to exercise tolerance in healthy Standardbred horses.

Methodology

• The researchers performed standardized exercise tests on horses on a high-speed treadmill, before and after administering clenbuterol.
• Six healthy Standardbreds were given the drug at a dosage of 0.8 micrograms/kg body weight twice a day for 5.5 days.
• Each horse underwent testing twice, once with a respiratory mask and once without, during two consecutive days.
• A week elapsed between the baseline tests without the drug and the tests with clenbuterol treatment, with each horse serving as its own control.

Results

• The results showed an unchanged heart rate response to exercise 2 hours after the last clenbuterol administration.
• There were no significant differences in the blood lactate response and the arterial oxygen tension during exercise before and after drug treatment.
• The work load performed relative to oxygen uptake and pulmonary ventilation was essentially unaffected by clenbuterol administration.
• The arterial pH during exercise significantly increased following clenbuterol treatment.
• The plasma levels of clenbuterol reached their highest 2 hours after administration, with values between 0.45 and 0.75 ng/ml, and the plasma half-life of elimination was 10.4 hours.

Conclusions

• The study concluded that clenbuterol did not cause major effects on the tested cardio-respiratory and blood lactate parameters in healthy horses performing submaximal exercise tolerance tests.