Dose-related effects of ethylketazocine on nociception, behaviour and autonomic responses in the horse.

The research investigates the effects of different amounts of ethylketazocine, an opioid, on pain, behaviour, and autonomic responses in horses. The study suggests that mu- and possibly kappa-receptors can mediate the actions of narcotics in horses.

Background

• The study is based on the idea that sensitive methods for measuring the analgesic, physiological and behavioural effects of opioids in horses have been developed recently. These methods have led to a deeper understanding of how narcotics work in horses.

Previous Research

• Past research indicated that Fentanyl, an example of a mu-opiate receptor agonist, caused a syndrome characterized by significant pain relief, stimulation of voluntary movement, rapid heart rate, quick breathing, and behavioural arousal.
• This study aimed to determine whether other opiate receptors mediate some of the effects of narcotic pain relievers in horses.

The Experiment

• Researchers introduced an agent with activity at kappa, and to a lesser extent mu-receptors, to a rigorous experimental protocol.
• The agent, ethylketazocine (EKC), was measured in varying doses (0.0025-0.012 mg kg-1 i.v.) to detect its effects.

Findings

• Like Fentanyl, EKC produced significant dose-related pain relief to painful thermal stimuli.
• It was reported that there were moderate dose-related increases in voluntary movement, pupil diameter and rectal temperature.
• However, unlike Fentanyl, EKC did not affect the cardiac or respiratory rates and caused behavioural sedation instead of arousal.

Conclusions

• The results of this study indicate that mu- and possibly kappa-receptors can mediate the actions of narcotics in horses.
• By using EKC, the researchers have demonstrated a different response in horses, which could lead to a better understanding of narcotics use in equine medicine.