Metabolic Fates of Ammonia–N in Ruminal Epithelial and Duodenal Mucosal Cells Isolated from Growing Sheep

• Published in: Journal of dairy science 2005-11, Vol.88 (11), p.3963-3970
• Main Authors: Oba, M., Baldwin, R.L., Owens, S.L., Bequette, B.J.
• Format: Article
• Language: English
• Subjects: Alanine - metabolism; amino acid metabolism; ammonia; Ammonia - metabolism; ammonium nitrogen; Animal productions; Animals; Arginine - metabolism; Aspartic Acid - metabolism; Biological and medical sciences; Citrulline - metabolism; cultured cells; duodenal mucosal cells; Duodenum - metabolism; epithelial cells; Epithelium - metabolism; Food industries; Fundamental and applied biological sciences. Psychology; Gas Chromatography-Mass Spectrometry; Glutamic Acid - metabolism; intestinal mucosa; Intestinal Mucosa - metabolism; Milk and cheese industries. Ice creams; Nitrogen - metabolism; Nitrogen Isotopes; Rumen - metabolism; rumen epithelium; rumen fermentation; ruminal epithelial cells; sheep; Sheep - metabolism; Terrestrial animal productions; urea; Urea - metabolism; Vertebrates
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.S0022-0302(05)73082-4

The objective of this experiment was to determine the capability of ruminant gut tissues to detoxify ammonia-N using short-term incubations of isolated cells in vitro. Ruminal epithelial cells (REC) and duodenal mucosal cells (DMC) were isolated from growing Texel-Polypay ram lambs (n=4) fed a pelleted forage:concentrate-based diet. Immediately after isolation, primary cells were incubated for 60min with glucose (1mM), glutamate (1mM), [15N]ammonium chloride (5, 10, 20, or 40mM), and 1 of 4 combinations of substrates (1mM each) that could support urea synthesis [control, N-carbamoylglutamate (NCG); NCG + ornithine (ONCG); and ONCG + aspartate (AONCG)]. Treatments were arranged in a 4×4 factorial design. Incorporation of ammonia-15N into alanine, citrulline, arginine, and urea was determined by gas chromatography-mass spectrometry. For both cell types, ammonia-N transfer to alanine was lower when incubation medium contained NCG compared with control, whereas use of ammonia-N for net alanine synthesis increased quadratically with ammonia concentration regardless of substrate treatment. For REC, ammonia-N was not incorporated into citrulline, arginine, or urea, nor into arginine or urea by DMC. Ammonia-N use for net citrulline synthesis exhibited an inverse relationship with ammonia concentration, decreasing linearly as media ammonia concentration increased. Thus, ala-nine synthesis may be a significant metabolic pathway for ruminant gut tissues to detoxify ammonia-N when it is presented luminally at high concentrations as compared with detoxification by the ornithine-urea cycle. Furthermore, DMC do exhibit a metabolic capability to incorporate ammonia-N into citrulline, but low or absent activity of downstream enzymes of the ornithine-urea cycle appears to limit ammonia-N transfers to urea.