Relaxing effects of clenbuterol, ritodrine, salbutamol and fenoterol on the contractions of horse isolated bronchi induced by different stimuli.

This research investigates the comparative effects of β-adrenoceptor agonists, such as clenbuterol, ritodrine, salbutamol, and fenoterol, on bronchial contractions in horses. The study found that fenoterol and salbutamol were more effective than commonly-used clenbuterol in relaxing these contractions.

Study Design and Methods

• The researchers examined four selective β agonists, known to counteract bronchoconstriction: clenbuterol, ritodrine, salbutamol, and fenoterol.
• They studied the effects of these drugs on contractions of isolated bronchial muscle in horses using different stimuli, including electrical field stimulation (EFS), carbachol, histamine, and KCl.

Results and Findings

• All the β agonists reduced the amplitude of contraction induced by the different stimulants, but the efficacy and potency varied.
• Fenoterol and salbutamol were more effective than clenbuterol in countering bronchial contractions induced by EFS and histamine.
• Fenoterol and salbutamol were also able to completely end contractions induced by carbachol, unlike clenbuterol and ritodrine.
• Potency values (pEC) were measured for each agonist and stimulant, showing different levels of impact, with fenoterol and salbutamol generally showing higher pEC values, indicating higher efficacy.
• Clenbuterol, despite its usual use in clinical practice, showed relatively low efficacy despite good potency. This may be due to being a partial agonist.
• Ritodrine displayed lower or not significantly different efficacy and potency when compared to the other agonists.

Implications and Conclusions

• The higher efficacy of salbutamol and fenoterol in relaxing horse bronchial muscle suggests they may be more effective bronchodilators than clenbuterol.
• The researchers recommend further clinical evaluation of the efficacy of fenoterol and salbutamol in treating horses with asthma. They could potentially be more effective bronchodilators compared to clenbuterol.