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, 2 mM ~-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 f 0.45 nmol . lo6 cells-' . 30 min-'), or from L-ornithine (0.29 -+ 0.06 nmol . 10' cells-' . 30 min-') 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 f 0.15 nmol . lo6 cells-' . 30 min-').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 Lcitrulline was very low in post-weaned animals, it was significantly enhanced in the presence of Lglutamine, 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.Apart from their well-identified function of nutrient translocation, including that of amino acids, from the intestinal lumen to the bloodstream, enterocytes are able to partially metabolize these amino acids during their transcellular journey. L-Glutamine is highly utilized by intestinal absorptive cells where it plays the role of a respiratory fuel [l]. In contrast, the oxidative catabolism of L-arginine in enterocytes is negligible relative to its conversion to L-ornithine and L-citrulline [2]. The adult intestine intensively degrades absorbed L-arginine resulting in a high L-ornithine, urea and L-citrulline release into blood [3]. Intestinal arginase cleaves L-arginine into L-ornithine and urea, and L-ornithine is considered as an important contributor to urea synthesis from excess ammonia in liver [4-61. Further metabolism of L-ornithine in adult intestine is limited to L-citrulline generation since a complete urea cycle does not operate in adult intestinal mucosa (71, the two enzymes responsible for the conversion of L-citrulline to L-arginine [argininosuccinate

Intestinal transport of nutrients coincides with their partial catabolism in the gut. The aim of the present study was to measure intestinal oxygen consumption and nutrient metabolism after a meal or during a short fast. Nutrient and oxygen balances across the small intestine were measured in conscious 50 kg (live wt) pigs. Jejunal enterocytes were also isolated from 1-hr postprandial, postabsorptive, or 3-day fasted pigs, in order to evaluate their capacities to metabolize 5 mM glucose and 2 mM glutamine. Whatever the nutritional state, intestinal oxygen consumption was high, since 26 +/- 2% (n = 6) of the oxygen arterial supply was extracted by the small intestine. Furthermore, the consumption of a mixed meal induced a rapid and transient rise in oxygen consumption. In the postabsorptive state, the intestinal uptake of glucose (0.31 +/- 0.08 mmole/min, n = 6) was twice higher than that of glutamine. The role of glucose as a fuel was also evidenced after a 3-day fast. During nutrient absorption, glutamine was highly utilized, and lactate was produced. The capacity of enterocytes isolated from fed pigs to metabolize glucose was dramatically reduced, as was 6-phosphofructo 1-kinase activity. In contrast, intestinal muscle presented a high glycolytic capacity from glucose, suggesting that the main site of intestinal lactate production during nutrient absorption would be the muscular rather than the epithelial layer.

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Energy metabolism in the colon has been poorly investigated. Feeding highly fermentable carbohydrates in the diet leads to an increased short chain fatty acid production in the colon, the effect of which on colonic mucosal metabolism is essentially unknown.

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