Postnatal changes of plasma amino acids in suckling pigs

Amino acids, ammonia, urea, orotate, and nitrate plus nitrite (stable oxida tion products of nitric oxide) were determined in plasma of 1- to 21-dold s uckling pigs. Jugular venous blood samples were obtained from pigs at 1, 3, 7, 14, and 21 d of age for analysis of plasma amino acids and metabolites by HPLC and enzymatic methods. Plasma concentrations of arginine and its im mediate precursors (citrulline and ornithine) decreased (P < 0.01) progress ively (20 to 41%) with increasing age from 3 to 14 d. Plasma concentrations of glutamine declined (P < 0.01) progressively (10 to 31%) during the Ist wk of life. Plasma concentrations of branched-chain amino acids, threonine, and alanine decreased (P < 0.01) (5 to 12%) in 14- and 21-d-old pigs, comp ared with 1- and 3-d-old pigs. There were no postnatal changes (P > 0.05) i n plasma concentrations of other amino acids. Plasma concentrations of ammo nia increased (P < 0.01) by 18 and 46%, whereas those of nitrate plus nitri te decreased (P < 0.01) by 16 and 29%, in 7- and 14-d-old pigs, respectivel y, compared with 1- to 3-d-old pigs. Because arginine plays a crucial role in ammonia detoxification via the hepatic urea cycle and is the physiologic al substrate for nitric oxide synthesis, our results of the decreased plasm a concentrations of arginine and nitrate plus nitrite, as well as the incre ased plasma ammonia concentration, indicate a hitherto! unrecognized defici ency of arginine, in 7- to 21-d-old suckling pigs. Arginine is an essential amino acid for piglets and has a great potential to enhance neonatal growt h; therefore, further studies are necessary to elucidate the mechanism resp onsible for arginine deficiency in sow-reared piglets and to identify hormo nal and metabolic means for improving neonatal arginine nutrition and growt h.