Intestinal arginine metabolism during development

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Abstract
The capacity for l-arginine metabolism was studied in villus enterocytes isolated from pigs at birth, after 2–8 days suckling and after weaning. Immediately after birth, enterocytes were able to convert 1 mM l-citrulline, 2mM l-glutamine or 1 mM l-ornithine to l-arginine. In 2–8-day-old animals, the net production of l-arginine from l-citrulline (2.00±0.45 nmol · 106 cells−1· 30 min−1), or from l-ornithine (0.29±0.06 nmol · 106 cells−1· 30 min−1) was similar to the values obtained at birth. Furthermore, 40% of l-arginine synthetized de novo from l-citrulline were released into the incubation medium. In 2–8-day-old animals, the production of l-arginine from l-glutamine represented only 5% of the production at birth (the latter being 0.73±0.15 nmol · 106 cells−1± 30 min−1). In enterocytes isolated from post-weaned pigs, no significant production of l-arginine from either l-glutamine or l-ornithine was detected. In contrast, although the l-arginine production from l-citrulline was very low in post-weaned animals, it was significantly enhanced in the presence of l-glutamine, representing 23% of the production measured in suckling animals. The capacity of enterocytes to cleave l-arginine to l-ornithine and urea was very limited at birth, but was increased more than threefold in 2-day-old animals. This was concomitant with a marked increase in arginase activity. In post-weaned animals, the flux through arginase in intact enterocytes, and the arginase activity were both threefold higher than in 2–8-day-old animals. It is concluded that enterocytes isolated from neonatal pigs exhibit the capacity for a net production of l-arginine since the metabolism of this amino acid is oriented to anabolism rather than catabolism. The results are discussed in relation to l-arginine metabolism in the neonatal liver.