Nitrogen metabolism in the gut.

All three of the major human nitrogenous waste products--urea,, creatinine, and uric acid--are significantly degraded by intestinal bacteria. The breakdown products of creatinine and uric acid are not fully known, but metabolites of these complex heterocyclic nitrogen compounds may well turn out to play a role in uremic toxicity. Urea degradation is almost certainly by way of ammonia, but the exact site of urea hydrolysis in the alimentary tract is not known, and it is uncertain whether urea is the major source of intestinal ammonia. Ammonia is absorbed from the colon predominantly in unionized form, and the bicarbonate ion secreted by the colonic mucosa plays an important role in facilitating this absorption.