AMINO-ACID PROFILE AND AROMATIC AMINO-ACID CONCENTRATION IN TOTAL PARENTERAL-NUTRITION - EFFECT ON GROWTH, PROTEIN-METABOLISM AND AROMATIC AMINO-ACID-METABOLISM IN THE NEONATAL PIGLET

1. The protein and amino acid utilization of two commercially available amino acid solutions, one egg-patterned (Vamin), the other human-milk-patterned (Vaminolact), were studied in piglets receiving total parenteral nutrition. It was hypothesized that Vaminolact was deficient in total aromatic amino acids, so a third group received a human-milk-patterned amino acid solution with added phenylalanine. 2. The piglets were on total parenteral nutrition for 8 days from day 2 or 3 of life. They all received a total energy intake of 1040kJ day(-1) kg(-1) with macronutrient intakes of 14.6g of amino acid, 27.4g of glucose and 9.4g of fat day(-1) kg(-1). 3. Nitrogen balances were performed on days 3-8 of total parenteral nutrition. On day 8 a primed constant infusion of (1-C-14]-phenylalanine was given to measure phenylalanine flux and fractional conversion to tyrosine. Transamination catabolites of phenylalanine and tyrosine were measured in urine on day 7. 4. The piglets receiving Vaminolact gained significantly less weight (0.86kg compared with 1.18kg for Vamin and 1.20kg for phenylalanine-supplemented Vaminolact; P<0.02) and nitrogen (1435mg day(-1) kg(-1) compared with 1601mg and 1836mg day(-1) kg(-1) for the other groups; P<0.0001). 5. The piglets receiving Vamin had high plasma phenylalanine levels (2234 mu mol/l compared with 156 mu mol/l for Vaminolact and 399 mu mol for phenylalanine-supplemented Vaminolact; P<0.0001). Those receiving Vamin also had an elevated excretion of phenylalanine transamination metabolites and low plasma lysine levels. Phenylalanine flux was highest in the Vamin group, intermediate in the phenylalanine-supplemented Vaminolact group and lowest in the Vaminolact group. 6. We conclude that Vaminolact is limiting in aromatic amino acids and that the addition of phenylalanine to the level in Vamin significantly improves growth and nitrogen retention; however, increasing the phenylalanine content of total parenteral nutrition is not the most metabolically suitable way to provide aromatic amino acids in neonatal total parenteral nutrition.