Arginine degradation in developing porcine enterocytes

Arginine degradation was quantified in enterocytes of 0-day-old (newborn) and 4- to 21-day-old suckling pigs and 29- to 58-day-old pigs weaned at 21 days of age. Cells were incubated at 37 degrees C for 30 min in 2 ml Krebs bicarbonate buffer (pH 7.4) in the presence of 0 or 2 mM L-[U-C-14] arginine or 0.5 mM L-[U-C-14]ornithine, with or without 2 mM N-G-nitro-L-arginine (L-NNA), 10 mM L-valine, or 2 mM gabaculine. Arginine degradation to CO2, ornithine, or proline was negligible in enterocytes of newborn and suckling pigs and markedly increased in weaned pigs. In cells from newborn pigs, citrulline generation from arginine was greater than that of ornithine plus CO2. Citrulline synthesis decreased during the first 2 wk after birth and increased in weaned pigs to the value similar to that in newborn pigs. CO2, citrulline, ornithine, and proline accounted for 1, 4, 37, and 55% of metabolized arginine carbons, respectively, in cells of postweaning pigs. The synthesis of citrulline from arginine decreased by >88% in the presence of L-NNA. The metabolism of arginine to CO2, ornithine, and proline and of ornithine to CO2 and proline decreased by >85% in the presence of valine and gabaculine, respectively. The activity of ornithine decarboxylase was low in enterocytes from 0- to 58-day-old pigs, <8% of that of nitric oxide (NO) synthase. The activity of pyrroline-5-carboxylate (P5C) dehydrogenase from 0- to 58-day-old pigs was <5% of that of P5C reductase, which resulted in the preferential conversion of arginine to proline. Our results demonstrate that 1) arginine degradation was negligible in enterocytes of newborn and suckling pigs both NO synthase and arginase pathways and 2) NO synthase plays a quantitatively minor role in arginine degradation by enterocytes.