An important role for endogenous synthesis of arginine in maintaining arginine homeostasis in neonatal pigs

This study was designed to test the hypothesis that endogenous arginine synthesis plays an important role in maintaining arginine homeostasis in neonatal pigs. Gabaculine was used as a suicide inhibitor of ornithine aminotransferase to decrease the intestinal conversion of glutamine-derived pyrroline-5-carboxylate (P-5-C) into ornithine, the precursor of both citrulline and arginine. Four-day-old suckling pigs received oral administration of 0.0 or 0.83 mg gabaculine/kg body wt every 4 h during a 12-h period from 6 A.M. to 6 P.M. Blood was collected from piglet's jugular vein at 6 A.M. and 6 P.M. after a 2-h isolation from sows. Gabaculine treatment decreased plasma concentrations of ornithine, citrulline, and arginine by 59, 52, and 76%, respectively, and increased those of glutamine and proline by 74 and 220%, respectively. The gabaculine treatment also increased plasma concentrations of leucine, taurine, and ammonia by 29, 42, and 20%, respectively. There were no differences in intramuscular concentrations of amino acids between control and gabaculine-treated pigs. Because P-5-C synthase (the enzyme required for synthesis of P-5-C from glutamate) was almost exclusively located in enterocytes of 4-day-old pigs, our data suggest that the intestinal production of citrulline plays an important role in endogenous synthesis of arginine and its homeostasis in neonatal pigs.