Citrulline is an effective arginine precursor in enterally fed neonatal piglets.
Although neonatal piglets can synthesize some arginine from proline, there is a limit to this synthesis, and piglets fed an arginine-deficient diet have diminished whole-body arginine status. To help elucidate where the limitation in arginine synthesis may occur, our objective was to determine the most effective arginine precursor in 1-wk-old enterally fed piglets. Piglets were administered either an arginine-deficient (basal) diet [1.15 mmol arginine/(kg.d)] or the basal diet supplemented with equimolar [9.18 mmol/(kg.d)] amounts of proline (+Pro), ornithine (+Orn), citrulline (+Cit) or arginine (+Arg) for 5 d (n = 5/diet). Daily blood samples were taken and indicators of whole-body arginine status including plasma amino acid, ammonia, and urea concentrations were measured. A primed, constant intragastric (i.g.) infusion of l-[U-(14)C]proline was given to measure the proline to arginine conversion, and intravenous (i.v.) and i.g. infusions of l-[guanido-(14)C]arginine were given to determine arginine flux and to quantify the splanchnic extraction of dietary arginine. Piglets fed the +Cit and +Arg diets had lower plasma ammonia and urea concentrations (P < 0.05) and higher plasma arginine concentrations (P < 0.0001) and arginine fluxes (P < 0.05) than piglets fed the other 3 diets. Piglets fed +Cit and +Arg had a lower proline to arginine conversion (P < 0.05). During first-pass splanchnic metabolism, 52% of the dietary arginine was extracted, and this extraction was not affected by whole-body arginine status (P > 0.05). These data indicate that citrulline, but not ornithine or proline, is an effective arginine precursor, and that either citrulline formation or availability appears to limit arginine synthesis in neonatal piglets.
Urschel
Kristine L
KL
Nutritional Science, University of Toronto, Toronto, ON, Canada.
Shoveller
Anna K
AK
Uwiera
Richard R E
RR
Pencharz
Paul B
PB
Ball
Ronald O
RO
D000596:Amino Acids / Q000008:administration & dosage / Q000097:blood*; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D001120:Arginine / Q000096:biosynthesis* / Q000378:metabolism; D002956:Citrulline / Q000008:administration & dosage / Q000378:metabolism*; D004032:Diet; D013552:Swine
D000596:Amino Acids; D002956:Citrulline; D001120:Arginine