Exercise induced hormonal and metabolic changes in Thoroughbred horses: effects of conditioning and acepromazine.

This study investigated the effects of conditioning and the administration of acepromazine on various hormonal and metabolic changes in Thoroughbred horses during exercise. The results indicated that conditioning does not significantly affect plasma potassium, erythrocyte potassium, insulin, or glucose levels. However, exercise leads to a surge in plasma potassium, glucose, and cortisol levels. Furthermore, acepromazine administration was found to reduce L-lactate concentration post-exercise and delay the return of erythrocyte potassium concentration to baseline levels.

Hormonal and Metabolic Changes in Thoroughbred Horses

• The study involved nine Thoroughbred horses and recorded changes in their insulin, glucose, cortisol, plasma potassium, and erythrocyte potassium levels during a conditioning period and following maximum exercise.
• Conditioning did not show any significant trends in altering these levels. However, serum cortisol increased from the first week but fell after the fifth week, suggesting a possible adaptation to the stress of training.
• The study found that maximal exercise increased glucose, cortisol, and plasma potassium levels in horses. At the same time, insulin and erythrocyte potassium levels decreased.
• Post-exercise measurements revealed that while potassium levels returned to normal within thirty minutes, glucose and cortisol continued to increase. Insulin levels also showed a post-exercise surge.

Effect of Acepromazine

• Acepromazine administration did not affect the levels of adrenaline and noradrenaline before or two minutes after the exercise. These hormones are typically released during stressful situations, implicating that the drug did not alter the stress response to exercise.
• Interestingly, when the horses were given acepromazine, lower concentrations of L-lactate were observed two and thirty minutes after exercising. L-lactate is an indicator of anaerobic metabolism, suggesting that acepromazine could potentially reduce the physiological stress of exercise.
• Moreover, the return of erythrocyte potassium concentration to baseline levels was delayed following exercise after acepromazine administration. This observation may indicate an effect of acepromazine on post-exercise recovery in horses.

Future Research Directions

• The study noted the need for further investigations to understand the implications of low erythrocyte K concentrations in performance horses better.
• Additionally, the beneficial role of acepromazine in limiting signs of exertional rhabdomyolysis (muscle breakdown due to extreme exercise) should be evaluated. The drug could potentially play an essential role in managing exercise-related physiological stress in horses.