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Adaptative increase of ornithine production and decrease of ammonia metabolism in rat colonocytes after hyperproteic
Béatrice Mouillé1, Véronique Robert, François Blachier
1Laboratoire de Nutrition et Sécurité Alimentaire, Institut National de la Recherche Agronomique, 78350 Jouy-en-Josas, France.
Summary
High-protein diets increase colon ammonia. Colon cells adapt by producing more ornithine to clear ammonia, but later reduce ammonia processing, suggesting a protective response.
Area of Science:
- Gastroenterology
- Nutritional Science
- Cellular Metabolism
Background:
- Chronic high-protein consumption elevates luminal ammonia (NH(4)(+)/NH(3)) in the colon.
- The impact of this ammonia increase on colonic epithelial cell metabolism is not fully understood.
Purpose of the Study:
- To investigate the consequences of increased luminal NH(4)(+)/NH(3) on colonic epithelial cell metabolism in rats.
- To determine if colonocytes adapt their ammonia metabolism in response to high-protein diets.
Main Methods:
- Rats were fed diets with 20% (P20) or 58% (P58) casein for 7 days.
- Measured luminal and portal vein NH(4)(+)/NH(3) concentrations.
- Assessed ammonia metabolism, including l-ornithine and urea production, in isolated colonocytes.
Main Results:
- The P58 diet significantly increased luminal and blood NH(4)(+)/NH(3) after 2 days.
- Colonocytes from P58 rats showed increased l-ornithine and urea production via arginase.
- After 7 days, P58 colonocytes had reduced ammonia metabolism to l-citrulline despite stable enzyme activity, coinciding with normalized blood ammonia.
Conclusions:
- Colonocytes increase l-ornithine synthesis to aid ammonia elimination, likely supporting the liver's urea cycle.
- Colonocytes reduce l-citrulline synthesis from l-ornithine, decreasing cellular ammonia utilization.
- These metabolic shifts represent an adaptive inter-organ response protecting against high luminal ammonia.
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