Effects of amitraz, several opiate derivatives and anticholinergic agents on intestinal transit in ponies.

The research explores the impact of various medical compounds on the digestive process in ponies, demonstrating that several substances—including amitraz, atropine, glycopyrrolate, and morphine—noticeably slow down digestion. Interestingly, the research also identifies that these effects might be achieved through different mechanisms depending on the drug, and may have potential applications in treating symptoms of gastrointestinal disorders in horses.

Substances and their effects

• The researchers evaluate a variety of substances, including amitraz (an insecticide), several opiate derivatives (including morphine and its variants meperidine, oxymorphone, and butorphanol), glycopyrrolate (a medication used to reduce saliva production), atropine (a medication used for a range of applications including dilating pupils), and loperamide (an anti-diarrhea medication).
• All of these substances, with the exception of morphine’s derivatives and loperamide, delayed intestinal transit in the ponies tested, which was observed through the use of a non-absorbable marker, polyethylene glycol (PEG).
• Despite all causing a delay in digestion, it is noted that the mechanisms causing these delays may differ widely between the substances.

Loperamide’s impact on intestinal transport

• Loperamide stood out in the research as it affected intestinal transport (the movement of fluid through the digestive system) rather than delaying the physical journey of food through the system.
• No significant delay in PEG transit was observed, indicating that although loperamide affects the intestine, it does not hinder the overall speed of digestion like the other substances.

Possible treatments and interventions

• The action of amitraz, which disrupts smooth muscle coordination and enhances absorption, was found to be linked to an alpha 2 adrenergic component, which is susceptible to yohimbine, a substance commonly used to reverse the effects of sedation in dogs and deer.
• The opiate antagonist naloxone did not influence the impacts of amitraz, but it was observed to stimulate the return of intestinal sounds and defecation after a refractory period in ponies dosed with morphine.
• The observed effects of these substances suggest potential clinical applications in horses, such as using loperamide for diarrhea therapy, alpha 2 adrenergic antagonists for obstructions and ileus (a disruption in the normal movement of the digestive system), and potentially amitraz-like agents for reducing fluid losses in cases of diarrhea.