Effects of enkephalins versus opiates on locomotor activity of the horse.

This research examines the effect of enkephalins and opiates on the locomotive behavior of horses, indicating that high dosages of enkephalins might increase locomotor activity but could also have potential negative side effects.

Introduction

• The study revolves around enkephalins – small neurotransmitter molecules believed to be used in racing horses. The researchers intended to evaluate their impact on the locomotor activity of horses.

Methodology

• The enkephalins D-Ala2-Metenkephalinamide and leucine enkephalin were administered to the horses through two methods – intravenous injection (IV) and intracisternal (IC).
• The doses of leucine enkephalin administered were 0.01 mg/Kg or less. The doses of methionine enkephalinamide given were 0.002 and 0.008 mg/kg via IV, and 0.005-.011 mg/Kg through IC method.
• On the other hand, the opiate fentanyl was administered IV (0.01 mg/Kg) or IC (0.0002 mg/Kg).

Findings

• Leucine enkephalin showed little effect on the horses’ locomotive activity, regardless of the injection method – IV or IC.
• Methionine enkephalinamide, an enzyme-resistant enkephalin analog, did not display significant effects when administered through IV. Administering it intracisternally at higher dosage, however, led to a number of physiological responses, including increased locomotor activity, rise in temperature, increase in blood pressure, hyperventilation, and noticeable rapid eye blinking reflex, lack of coordination, and quivering.
• On the contrary, the use of fentanyl caused a tenfold increase in locomotor activity, with no accompanying negative clinical symptoms.

Conclusion

• The study suggested that massive doses of IV-administered enkephalins or their analogs might enhance locomotor activity, but they may also incite several less desirable side effects. Further research is needed to study these effects and investigate potential ways to mitigate them.