title: Evaluation of the effect of ranitidine on gastroduodenal contractile activity and gastric emptying in horses.
abstract: OBJECTIVE
  To determine the effect of ranitidine on gastric emptying in horses.
  
  
  METHODS
  11 adult horses.
  
  
  METHODS
  In vitro, isolated muscle strips from the pyloric antrum and duodenum of 5 horses were suspended in baths and attached to isometric force transducers. Once stable spontaneous contractions were observed, ranitidine or diluent was added at cumulative increasing concentrations. Isometric stress responses were compared. In vivo, 6 horses were assigned to a group in a prospective randomized crossover study design with a wash-out period of 2 weeks between trials. Ranitidine (2.2 mg/kg) or saline (0.9% NaCl) solution was administered IV, and 15 minutes later, acetaminophen (20 mg/kg), diluted in 400 mL of water, was administered via nasogastric tube to evaluate the liquid phase of gastric emptying. Serum acetaminophen concentration was measured at several time points for 3 hours by use of liquid chromatography tandem mass spectrometry. Frequency of defecation was recorded during the 3 hours of the study.
  
  
  RESULTS
  Ranitidine increased the contractile activity of the pyloric antrum smooth muscle at a concentration of 10(-4) M. No significant effect of ranitidine on plasma kinetics of acetaminophen was identified. Frequency of defecation did not differ between groups.
  
  
  CONCLUSIONS
  Ranitidine did increase gastric motility in vitro, but no effect on liquid phase gastric emptying was identified in healthy horses by use of the acetaminophen absorption model. Results do not support the use of ranitidine to promote gastric emptying.
authors.affiliation: Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
authors.forename: Omar
authors.initials: O
authors.lastname: Maher
authors.forename: Jorge E
authors.initials: JE
authors.lastname: Nieto
authors.forename: Scott D
authors.initials: SD
authors.lastname: Stanley
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Dore
authors.forename: Jack R
authors.initials: JR
authors.lastname: Snyder