AN IMPORTANT ROLE FOR ENDOGENOUS SYNTHESIS OF ARGININE IN MAINTAININGARGININE HOMEOSTASIS IN NEONATAL PIGS

This study was designed to test the hypothesis that endogenous arginin e synthesis plays an important role in maintaining arginine homeostasi s in neonatal pigs. Gabaculine was used as a suicide inhibitor of orni thine aminotransferase to decrease the intestinal conversion of glutam ine-derived pyrroline-5-carboxylate (P-5-C) into ornithine, the precur sor of both citrulline and arginine. Four-day-old suckling pigs receiv ed 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 ornithi ne, citrulline, and arginine by 59, 52, and 76%, respectively, and inc reased those of glutamine and proline by 74 and 220%, respectively. Th e 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 co ntrol 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 i ntestinal production of citrulline plays an important role in endogeno us synthesis of arginine and its homeostasis in neonatal pigs.