INTESTINAL ARGININE METABOLISM DURING DEVELOPMENT - EVIDENCE FOR DE-NOVO SYNTHESIS OF L-ARGININE IN NEWBORN PIG ENTEROCYTES

The capacity for L-arginine metabolism was studied in villus enterocyt es isolated from pigs at birth, after 2-8 days suckling and after wean ing. Immediately after birth, enterocytes were able to convert 1 MM L- citrulline, 2 mM 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.10(6) cells-1.30 min-1), or from L-ornithine (0.29 +/- 0.06 nmol.10(6) cells-1.30 min-1) was similar to the values obtain ed at birth. Furthermore, 40% Of L-arginine synthetized de novo from L -Citrulline were released into the incubation medium. In 2-8-day-old a nimals, the production Of L-arginine from L-glutamine represented only 5% of the production at birth (the latter being 0.73 +/- 0.15 nmol.10 (6) cells-1.30 min-1). In enterocytes isolated from post-weaned pigs, no significant production of L-arginine from either L-glutamine or L-o rnithine was detected. In contrast, although the L-arginine production from L-citrulline was very low in post-weaned animals, it was signifi cantly enhanced in the presence of L-glutamine, representing 23% of th e production measured in suckling animals. The capacity of enterocytes to cleave L-arginine to L-ornithine and urea was very limited at birt h, but was increased more than threefold in 2-day-old animals. This wa s concomitant with a marked increase in arginase activity. In post-wea ned animals, the flux through arginase in intact enterocytes, and the arginase activity were both threefold higher than in 2-8-day-old anima ls. It is concluded that enterocytes isolated from neonatal pigs exhib it the capacity for a net production of L-arginine since the metabolis m 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.