ABSTRACT
The lining cells of the mucosa in the fermentative part of the intestinal tract have metabolic pathways which are so adjusted to bacterial metabolites that mucosal function is impaired by the absence of bacteria. Ingested food in man is foremostly degraded by acid hydrolysis or enzymatic cleavage by proteases, by lipases and by saccharidases found in small bowel which is sparsely populated by bacteria. The opposite prevails in the pre- and post-gastric fermentative chambers and organs in which not enzymes but bacteria degrade oligosaccharides, oligopeptides, and fiber. Luminal pH depends upon the production rate of short-chain fatty acids by bacteria and the luminal appearance of bicarbonate which maintains the luminal pH at 7.4 with little variation. The interdependence between nitrate, mucosa, and bacteria is demonstrated by the fact that the colon extracts ingested nitrite. The action of nitrite anions traversing the colonic mucosa has not been studied before but we have recently shown that colonocytes are not endangered by nitrite.
