Lysine requirement of neonatal piglets receiving total parenteral nutrition as determined by oxidation of the indicator amino acid L-[1-14C]phenylalanine.

The indicator amino acid oxidation technique was adapted for use during total parenteral nutrition. Twenty-one male Yorkshire piglets (3 d of age) fitted with jugular and femoral vein catheters, received total parenteral nutrition for 6 d. Total parenteral nutrition included 15 g amino acids .kg-1.d-1 (1.25 g lysine.kg-1.d-1), lipid + glucose (1.1 MJ.kg-1.d-1), and micronutrients. Piglets were randomly assigned to lysine intakes of 0.40, 0.55, 0.70, 0.85, 1.00, 1.15, or 1.30 g.kg-1.d-1 and received a 4-h primed, constant infusion of L-[1-14C]phenylalanine. Phenylalanine oxidation (% of dose) decreased significantly (P < 0.05) from 18.6% at the lowest lysine intake to 3.0% at a lysine intake of 0.85 g.kg-1.d-1. Further increases in lysine intake had no effect on phenylalanine oxidation. Regression analysis yielded a mean lysine requirement of 0.79 g.kg-1.d-1 and a safe intake (upper 95% confidence limit) of 0.84 g.kg-1.d-1. Changes in the plasma lysine concentration and phenylalanine oxidation rates supported this estimate. The indicator amino acid oxidation technique can now be used to determine amino acid requirements during total parenteral nutrition. This means that the ideal amino acid pattern for neonates receiving total parenteral nutrition can now be defined by a sensitive and minimally invasive measurement of amino acid kinetics.