title: Oxalate Concentrations in Human Gastrointestinal Fluid.
abstract: OBJECTIVE
  Urinary oxalate excretion is a risk factor for nephrolithiasis and is a result of endogenous metabolism and gastrointestinal processes. Gastrointestinal absorption of oxalate has been well demonstrated but to our knowledge evidence for secretion of oxalate is absent in humans. The objective of this study was to measure the amount and conformation of oxalate in the stomach and small intestine of adult subjects undergoing gastrointestinal endoscopy.
  
  
  METHODS
  Eleven adults participated in this study. Gastrointestinal fluid was collected from the stomach and small intestine during endoscopy. A determination of the soluble and insoluble components of oxalate was made by centrifugation of the sample and subsequent acidification of the resultant pellet and supernatant. Samples were processed and the amount of oxalate was measured by ion chromatography, the limit of which is 1.6 μM.
  
  
  RESULTS
  The majority of small intestinal samples contained some degree of oxalate. This is in contrast to the stomach where minimal oxalate was detected. There was a wide range of oxalate concentrations and a greater degree of insoluble oxalate in small intestinal samples.
  
  
  CONCLUSIONS
  Our results suggest that some degree of oxalate secretion in the small intestine may occur in the fasted state while this is less likely in the stomach. Further studies are warranted to provide definitive evidence of gastrointestinal secretion of oxalate.
authors.affiliation: 1 Department of Urology, University of Alabama at Birmingham School of Medicine , Birmingham, Alabama.
authors.forename: Thanmaya G
authors.initials: TG
authors.lastname: Reddy
authors.affiliation: 1 Department of Urology, University of Alabama at Birmingham School of Medicine , Birmingham, Alabama.
authors.forename: John
authors.initials: J
authors.lastname: Knight
authors.affiliation: 1 Department of Urology, University of Alabama at Birmingham School of Medicine , Birmingham, Alabama.
authors.forename: Ross P
authors.initials: RP
authors.lastname: Holmes
authors.affiliation: 1 Department of Urology, University of Alabama at Birmingham School of Medicine , Birmingham, Alabama.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Harvey
authors.affiliation: 1 Department of Urology, University of Alabama at Birmingham School of Medicine , Birmingham, Alabama.
authors.forename: April L E
authors.initials: AL
authors.lastname: Mitchem
authors.affiliation: 2 Division of Gastroenterology and Hepatology, University of Alabama at Birmingham School of Medicine , Birmingham, Alabama.
authors.forename: Charles M
authors.initials: CM
authors.lastname: Wilcox
authors.affiliation: 2 Division of Gastroenterology and Hepatology, University of Alabama at Birmingham School of Medicine , Birmingham, Alabama.
authors.forename: Klaus E
authors.initials: KE
authors.lastname: Monkemuller
authors.affiliation: 1 Department of Urology, University of Alabama at Birmingham School of Medicine , Birmingham, Alabama.
authors.forename: Dean G
authors.initials: DG
authors.lastname: Assimos
mesh_terms: D000328:Adult; D000368:Aged; D002852:Chromatography, Ion Exchange / Q000379:methods; D016099:Endoscopy, Gastrointestinal; D005215:Fasting / Q000378:metabolism; D005260:Female; D005753:Gastric Mucosa / Q000378:metabolism; D006801:Humans; D007408:Intestinal Absorption; D007421:Intestine, Small / Q000737:chemistry* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D053040:Nephrolithiasis; D010070:Oxalates / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D013270:Stomach / Q000737:chemistry*
chemical_list: D010070:Oxalates