ARGININE DEGRADATION IN DEVELOPING PORCINE ENTEROCYTES

Arginine degradation was quantified in enterocytes of 0-day-old (newbo rn) and 4- to 21-day-old suckling pigs and 29- to 58-day-old pigs wean ed 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. A rginine degradation to CO2, ornithine, or proline was negligible in en terocytes of newborn and suckling pigs and markedly increased in weane d pigs. In cells from newborn pigs, citrulline generation from arginin e was greater than that of ornithine plus CO2. Citrulline synthesis de creased during the first 2 wk after birth and increased in weaned pigs to the value similar to that in newborn pigs. CO2, citrulline, ornith ine, and proline accounted for 1, 4, 37, and 55% of metabolized argini ne 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 orn ithine 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 nitr ic oxide (NO) synthase. The activity of pyrroline-5-carboxylate (P5C) dehydrogenase from 0- to 58-day-old pigs was <5% of that of P5C reduct ase, which resulted in the preferential conversion of arginine to prol ine. Our results demonstrate that 1) arginine degradation was negligib le in enterocytes of newborn and suckling pigs both NO synthase and ar ginase pathways and 2) NO synthase plays a quantitatively minor role i n arginine degradation by enterocytes.