In vivo and in vitro effects of neostigmine on gastrointestinal tract motility of horses.

This research investigates the impact of the drug neostigmine on the movement of the gastrointestinal tract in horses. It concludes that administering neostigmine to horses led to an increase in fecal production and the frequency of urination, and also stimulated contractile activity within parts of the gastrointestinal tract.

Study Design and Approach

• This research utilised a crossover study design that involved seven adult horses who received either a continuous rate infusion (CRI) of neostigmine (0.008 mg/kg/h) or a placebo. This methodology ensured that the processes remained the same for all subjects apart from the nature of the substance they were administered.
• Contractile activity within the jejunum and pelvic flexure were observed and reported upon.

Outcome Measurement

• Gastric emptying was assessed via the acetaminophen test. This test involves checking the time taken for plasma acetaminophen concentration to reach its peak and the rate of absorption.
• Throughout the experiment, data was collected on the number of times the horses defecated and urinated, along with the consistency and weight of their feces.

Key Findings

• The researchers found no variation between the impact of neostigmine and the placebo on the time needed to reach the top plasma acetaminophen concentration or absorption rate constant.
• The CRI of neostigmine was seen to elevate the fecal production and the frequency of urination in horses.
• Neostigmine led to a dose-related increase in contractile amplitude within the jejunum and pelvic flexure muscle strips.

Effects Following Incubation with Different Substances

• Incubation of muscle strips with muscarinic receptors antagonists (atropine and DAU 5884) inhibited response to acetylcholine and neostigmine.
• When smooth muscle strips from the jejunum were incubated with an acetylcholinesterase inhibitor (edrophonium), it heightened the response to acetylcholine but did not affect the response to neostigmine.

Study Conclusion

• The study revealed that administering neostigmine to horses escalated fecal production and urination frequency.
• It also showed that neostigmine does not reduce gastric emptying within horses.
• The research concluded that neostigmine successfully stimulated contractile activity within the jejunum and pelvic flexure smooth muscle strips in an in vitro environment.