Effects of caffeine and promazine hydrochloride on plasma catecholamines in thoroughbreds at rest and during treadmill exercise.

The research investigates the impact of caffeine and promazine hydrochloride (PRZ), substances often used for ‘doping’ in sport, on adrenaline (Ad) and noradrenaline (NA) levels in Thoroughbreds at rest and during exercise.

Experimental Procedure

• The study involved administering caffeine or PRZ intramuscularly to Thoroughbreds and then analyzing the effects on the plasma levels of Ad and NA both at rest and during exercise.
• Prior to exercise, the effects were compared to a saline control, while the exercise was undertaken on a treadmill an hour after the drug administration.

Caffeine Results

• Researchers found that an administration of 5mg/kg body weight (bwt) of caffeine significantly raised plasma levels of both Ad and NA, while the lower dose of 2.5mg/kg bwt did not have the same effect.
• The peak levels of Ad and NA following caffeine administration were approximately three and 2.5 times higher than the control values, respectively.
• The lower dose of caffeine also lead to a significant increase in Ad and NA during exercise.

PRZ Results

• Both 1.0mg and 1.5mg/kg bwt PRZ doses were found to lower plasma Ad to below the detection threshold and significantly brought down plasma NA.
• The 1.5mg/kg bwt PRZ dosage was found to lower plasma Ad during exercise, but the result was not statistically significant.
• Interestingly, PRZ led to a significant increase in plasma NA when compared to the saline control.

Conclusion

• Overall, the study demonstrates that the plasma responses to both caffeine and PRZ were indeed altered by exercise, likely due to the exercise-induced activation of the sympathetico-adrenal axis of the horses.
• While the effect of the drugs in raising the levels of Ad and NA at rest and during exercise was significant, it should be noted that the used doses were quite high in comparison to what would be typically used in a sporting context.