Effect of butorphanol on equine antroduodenal motility.

This research investigates how butorphanol, an analgesic drug usually used for pain management, affects the stomach and upper intestine (antroduodenal) movements in horses. The experiment finds that a standard analgesic dose of butorphanol resets these movements without causing any perceived negative effect, potentially providing improved gastrointestinal comfort for treated horses.

Experiment Methods

• This study was conducted on six healthy horses aged six to eight months. To monitor gut motion, Ag bipolar electrodes were surgically implanted onto the gastric antrum and duodenum, two sections of the horses’ gut. Wires from the electrodes were then brought out of the body from an incision in the side (flank) of the horse.
• The horses were mildly restrained and the electrode wires attached to a physiograph. This device was used to record the electrical signals associated with stomach and intestinal muscle contraction and relaxation – the antroduodenal myoelectrical activity.

Drug Administration and Results

• Each horse was given an intravenous dose of 0.05 mg/kg of butorphanol, an opioid drug that acts both as an agonist and antagonist. This drug dose is known to effectively manage pain in horses suffering from colic, a common gastrointestinal disorder in horses.
• Within 2 to 3 minutes of the butorphanol injection, the researchers registered a normal period of frequent spike activity (phase III) of the migrating motor complex (MMC) in the duodenum.
• This spike activity was followed by a period of no observable spike activity (phase I), then resumption of less frequent, intermittent spike activity (phase II). The latter two phases are also constituents of a normal MMC cycle. The MMC is a pattern of electrical activity and associated muscular movement that in sequence, perform the ‘housework’ of your gut like propelling indigestible substances.

Further Tests and Conclusions

• To investigate the mode of action of butorphanol, the experimenters pre-treated the horses with naloxone, a non-selective opioid antagonist, and tolazoline, an alpha 2-adrenergic antagonist. Neither drug was able to block the myoelectrical response to butorphanol, suggesting that butorphanol’s action may not involve a2-adrenergic or opioid receptors, or at least not in a conventional way.
• The researchers concluded that a dose of butorphanol known to provide effective pain relief in horses doesn’t adversely affect gut movement. However, further research is required to fully understand how butorphanol is able to reset the MMC activity, considering their investigations of its interaction with known receptor systems.