The effect of adrenergic suppression induced by guanabenz administration on exercising thoroughbred horses.

The study explores the effect of an antihypertensive drug, guanabenz, on race horses under intense exercise. The research suggests that guanabenz suppresses adrenergic activity, potentially improving the horses’ endurance.

Methods

• In this study, a random crossover design was used. The 12 Thoroughbred horses that participated were exercise conditioned.
• The horses were each given guanabenz at a dosage of 0.08 mg per kg of body weight intravenously and a placebo at three-week intervals.
• One hour post-treatment, each horse underwent an incremental exercise test on a treadmill until exhaustion.
• Various metrics related to heart function and metabolism were monitored during the exercise phase. These included heart rate, oxygen consumption, carbon dioxide output, plasma lactate, catecholamines as well as adrenocorticotropic hormone (ACTH) and cortisol.
• The time taken to reach fatigue was also measured.
• A statistical analysis of the collected data was done using mixed-effects linear modelling.

Results

• It was found that the mean heart rate during exercise was lower in horses that were treated with guanabenz. The p-value for this was significant at 0.04.
• Similarly, mean plasma cortisol and adrenaline levels were lower in horses treated with guanabenz during the exercise period, with significant P values of 0.02 and 0.03 respectively.
• While average running time was slightly longer in the guanabenz treated group, the difference was not statistically significant (P value of 0.053).
• No significant differences were seen based on guanabenz treatment in relation to oxygen consumption, carbon dioxide output, plasma lactate, noradrenaline, and ACTH concentrations.

Conclusions

• The study concluded that guanabenz administration led to signs of adrenergic suppression as evidenced by lower average plasma cortisol and adrenaline levels, and heart rate.
• This might hint towards potential enhancement of endurance in horses subjected to intense exercise.
• However, the researchers pointed out that guanabenz did not completely remove the increase in hormone levels induced by intense exercise.
• The researchers suggest that further determination of a positive performance effect due to adrenaline suppression (but not noradrenaline) is required before the clinical significance of guanabenz administration in racing horses can be fully understood.