Colonic luminal ammonia and portal blood L-glutamine and L-arginine concentrations: a possible link between colon mucosa and liver ureagenesis.
The highest ammonia concentration in the body is found in the colon lumen and although there is evidence that this metabolite can be absorbed through the colonic epithelium, there is little information on the capacity of the colonic mucosa to transfer and metabolize this compound. In the present study, we used a model of conscious pig with a canula implanted into the proximal colon to inject endoluminally increasing amounts of ammonium chloride and to measure during 5 h the kinetics of ammonia and amino acid concentration changes in the portal and arterial blood. By injecting as a single dose from 1 to 5 g ammonia into the colonic lumen, a dose-related increase in ammonia concentration in the portal blood was recorded. Ammonia concentration remained unchanged in the arterial blood except for the highest dose tested, i.e. 5 g which thus apparently exceeds the hepatic ureagenesis capacity. By calculating the apparent net ammonia absorption, it was determined that the pig colonic epithelium has the capacity to absorb 4 g ammonia. Ammonia absorption through the colonic epithelium was concomitant with increase of L-glutamine and L-arginine concentrations in the portal blood. This coincided with the expression of both glutamate dehydrogenase and glutamine synthetase in isolated colonic epithelial cells. Since L-glutamine and L-arginine are known to represent activators for liver ureagenesis, we propose that increased portal concentrations of these amino acids following increased ammonia colonic luminal concentration represent a metabolic link between colon mucosa and liver urea biosynthesis.
Eklou-Lawson
Mamy
M
INRA, CNRH-IdF, AgroParisTech, UMR 914 Nutrition Physiology and Ingestive Behavior, 16 rue Claude Bernard, 75005, Paris, France.
Bernard
Françoise
F
Neveux
Nathalie
N
Chaumontet
Catherine
C
Bos
Cécile
C
Davila-Gay
Anne-Marie
AM
Tomé
Daniel
D
Cynober
Luc
L
Blachier
François
F
D000641:Ammonia / Q000097:blood / Q000378:metabolism*; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001120:Arginine / Q000032:analysis / Q000097:blood / Q000378:metabolism*; D005969:Glutamate Dehydrogenase / Q000187:drug effects / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000187:drug effects / Q000378:metabolism; D005973:Glutamine / Q000032:analysis / Q000097:blood / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D011169:Portal Vein / Q000378:metabolism*; D034421:Sus scrofa; D014508:Urea / Q000819:agonists / Q000097:blood / Q000378:metabolism*
D000643:Ammonium Chloride; D005973:Glutamine; D000641:Ammonia; D014508:Urea; D001120:Arginine; D005969:Glutamate Dehydrogenase; D005974:Glutamate-Ammonia Ligase