Developmental Amino Acid Metabolism in the Pig Small and Large Intestine Epithelial Cells
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2013 Springer-Verlag Wien. All rights reserved. From experimental works performed on pigs, it appears clearly that a significant part of several dispensable and indispensable amino acids present in the small intestine content are metabolized during their transcellular journey through the small intestine epithelial cells (enterocytes) when moving from the luminal side of the intestine to the portal bloodstream. Importantly, this metabolism in enterocytes is different according to the pig developmental stages, and we will see in this chapter that this has important metabolic and physiological consequences. It has been determined that some amino acids are catabolized in enterocytes and some other amino acids are generated by the small intestine epithelium. These results are mostly derived from both in vivo and in vitro experiments. A major in vivo experimental design used to estimate the apparent amino acid intestinal absorption is the porto-arterial balance sheet which consists of measuring the amino acid concentrations at different time following a meal in both the arterial and portal blood as well as measuring continuously the blood flow in the portal vein. This allows to have an estimation of the apparent intestinal absorption of amino acids as well as to presume if a given amino acid is globally degraded or generated during its transport through the intestinal mucosa. Although very informative, these in vivo methods are limited by the fact that the portal vein does not exclusively drain amino acids from the intestine but also from other visceral tissues (notably stomach, pancreas, and spleen). Numerous teams in the world have also used alimentary proteins labelled with stable isotope to estimate the metabolic fate of amino acids during their intestinal absorption and further on in the body.
