title: In vitro validation of the lactose 13C-ureide breath test for equine orocaecal transit time measurement.
abstract: BACKGROUND
  Validation of a reliable, noninvasive clinical test for quantification of equine orocaecal transit time (OCTT) is required. This would facilitate an evidence-based approach to investigation and treatment of equine small intestinal disorders.
  
  
  OBJECTIVE
  1) Comparison of the lactose (13) C-ureide breath test (LUBT) with the hydrogen breath test (H(2) BT) for OCTT measurement. 2) Identification of the characteristics of gastrointestinal microbial glycosylureide hydrolase activity in vitro. 3) Production of an optimised protocol for the LUBT for in vivo measurement of equine OCTT.
  
  
  OBJECTIVE
  Significant lactose (13) C-ureide ((13) C-LU) hydrolase activity is restricted to the large bowel. The rate of expiratory (13) CO(2) production after ingestion of the isotope will provide an indirect quantifiable measure of orocaecal transit rate. Requisite bacterial activity may be enhanced by a primer dose of unlabelled substrate as shown in Man.
  
  
  METHODS
  Combined LUBT and H(2) BT were performed in 8 healthy individuals. Analysis of sequential end expiratory breath samples was used to calculate OCTT and results compared. Digestion of (13) C-LU was investigated in vitro using fresh faecal material or intestinal aliquots collected post mortem. Isotopic fermentation rate was measured by rate of appearance of (13) CO(2) .
  
  
  RESULTS
  Peaks in expiratory (13) CO(2) occurred in all individuals after ingestion of the labelled test meal, whereas H(2) expiration was variable. Both faecal and intestinal microbial digestion of (13) C-LU were maximised by prior exposure to (12) C-LU. Induced bacterial glucoseureide hydrolase activity was significantly greater in the caecum than in the small intestine (n = 10, P<0.05).
  
  
  CONCLUSIONS
  Significant (13) C-LU digestion is restricted to the equine large intestine under normal conditions, and is enhanced by prior exposure to (12) C-LU, making (13) C-LU a suitable noninvasive marker of equine OCTT. The LUBT is more reliable than the H(2) BT for measurement of equine OCTT.
authors.affiliation: School of Veterinary Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, UK. david.sutton@glasgow.ac.uk
authors.forename: D G M
authors.initials: DG
authors.lastname: Sutton
authors.forename: T
authors.initials: T
authors.lastname: Preston
authors.forename: S
authors.initials: S
authors.lastname: Love
mesh_terms: D000818:Animals; D001944:Breath Tests / Q000379:methods*; D002247:Carbon Isotopes; D002432:Cecum; D005285:Fermentation; D005772:Gastrointestinal Transit / Q000502:physiology*; D006736:Horses / Q000502:physiology*; D007785:Lactose / Q000378:metabolism*; D009055:Mouth; D015203:Reproducibility of Results; D013997:Time Factors; D014508:Urea / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; C121442:lactose ureide; D014508:Urea; D007785:Lactose