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Threonine requirement of parenterally fed postsurgical human neonates^1,2,3

¹ From the Research Institute, The Hospital for Sick Children, Toronto, Canada (KPC, GC-M, AMM, and PBP); the Departments of Nutritional Sciences and Paediatrics, University of Toronto, Toronto, Canada (KPC, GC-M, PBP, ROB, and AMM); and the Department of Agriculture, Food, and Nutritional Science, University of Alberta, Edmonton, Canada (ROB and PBP).

² Supported by grant no. FRN 12928 from the Canadian Institutes for Health Research, scholarships from the Strategic Training Institute in Health Research and the Canadian Institute of Health Research (to KPC and GC-M), and the Clinician Scientist Training Program, the Hospital for Sick Children, Toronto, Canada (GC-M). Glycyl-L-tyrosine was supplied by Baxter Canada (Mississauga, Canada).

³ Reprints not available. Address correspondence to PB Pencharz, Division of Gastroenterology, Hepatology and Nutrition, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada M5G 1X8. E-mail: paul.pencharz{at}sickkids.ca.

Background: The threonine requirement of human neonates who receive parenteral nutrition (PN) has not been determined experimentally.

Objective: The objective was to determine the parenteral threonine requirement for human neonates by using the minimally invasive indicator amino acid oxidation technique with L-[1-¹³C]phenylalanine as the indicator amino acid.

Design: Nine postsurgical neonates were randomly assigned to 16 threonine intakes ranging from 10 to 100 mg · kg^–1 · d^–1. Breath and urine samples were collected at baseline and at plateau for ¹³CO₂ and amino acid enrichment, respectively. The mean threonine requirement was determined by applying a 2-phase linear regression crossover analysis to the measured rates of ¹³CO₂ release (F¹³CO₂) and L-[1-¹³C]phenylalanine oxidation.

Results: The mean threonine parenteral requirement determined by using phenylalanine oxidation was 37.6 mg · kg^–1 · d^–1 (upper and lower confidence limits, respectively: 29.9 and 45.2 mg · kg^–1 · d^–1) and by using F¹³CO₂ oxidation was 32.8 mg · kg^–1 · d^–1 (upper and lower confidence limits, respectively: 29.7 and 35.9 mg · kg^–1 · d^–1). Graded intakes of threonine had no effect on phenylalanine flux.

Conclusion: This is the first study to report on the threonine requirement for human neonates receiving PN. We found that the threonine requirement for postsurgical PN-fed neonates is 22–32% of the content of threonine that is presently found in commercial PN solutions (111–165 mg · kg^–1 · d^–1).