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Eklou-Lawson Mamy Bernard Françoise Neveux Nathalie Chaumontet Catherine Bos Cécile Davila-Gay Anne-Marie Tomé Daniel Cynober Luc Blachier François 《Amino acids》2009,37(4):751-760
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. 相似文献
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