Evaluation of the effects of the opioid agonist morphine on gastrointestinal tract function in horses.
OBJECTIVE
To evaluate the effects of morphine administration for 6 days on gastrointestinal tract function in healthy adult horses.


METHODS
5 horses.


METHODS
Horses were randomly allocated into 2 groups in a crossover study. Horses in the treatment group received morphine sulfate at a dosage of 0.5 mg/kg, IV, every 12 hours for 6 days. Horses in the control group received saline (0.9% NaCl) solution at a dosage of 10 mL, IV, every 12 hours for 6 days. Variables assessed included defecation frequency, weight of feces produced, intestinal transit time (evaluated by use of barium-filled spheres and radiographic detection in feces), fecal moisture content, borborygmus score, and signs of CNS excitement and colic.


RESULTS
Administration of morphine resulted in gastrointestinal tract dysfunction for 6 hours after each injection. During those 6 hours, mean +/- SD defecation frequency decreased from 3.1 +/- 1 bowel movements in control horses to 0.9 +/- 0.5 bowel movements in treated horses, weight of feces decreased from 4.1 +/- 0.7 kg to 1.1 +/- 0.7 kg, fecal moisture content decreased from 76 +/- 2.7% to 73.5 +/- 2.9%, and borborygmus score decreased from 13.2 +/- 2.9 to 6.3 +/- 3.9. Mean gastrointestinal transit time was also increased, compared with transit times in control horses.


CONCLUSIONS
Morphine administered at 0.5 mg/kg twice daily decreased propulsive motility and moisture content in the gastrointestinal tract lumen. These effects may predispose treated horses to development of ileus and constipation.
Boscan
Pedro
P
Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Van Hoogmoed
Linda M
LM
Farver
Thomas B
TB
Snyder
Jack R
JR
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D018592:Cross-Over Studies; D005243:Feces / Q000737:chemistry; D005766:Gastrointestinal Contents / Q000187:drug effects; D041981:Gastrointestinal Tract / Q000187:drug effects* / Q000502:physiology*; D005772:Gastrointestinal Transit / Q000187:drug effects*; D006736:Horses / Q000378:metabolism*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D014867:Water / Q000032:analysis
D000701:Analgesics, Opioid; D014867:Water; D009020:Morphine