Proteolysis and phenylalanine hydroxylation in response to parenteral nutrition in extremely premature and normal newborns

Scott C. Denne, Cheryl A. Karn, Julie A. Ahlrichs, Asuncion R. Dorotheo, Junying Wang, Edward A. Liechty

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89 Scopus citations


To determine to what extent intravenous nutrition can reduce pruteolysis in very immature and normal newborns, and to assess the capacity of preterm and normal newborns to convert phenylalanine to tyrosine, phenylalanine and leucine kinetics were measured under basal conditions and daring parenteral nutrition in clinically stable, extremely premature (~ 26 wk of gestation) infants and in normal term newborns. In response to parenteral nutrition, there was significantly less suppression (P < 0.001) of endogenous leucine and phenylalanine rate of appearance in extremely premature infants compared with term infants. Phenylalanine utilization for protein synthesis during parenteral nutrition increased significantly (P < 0.01) and by the same magnitude (~ 15%) in both extremely premature and term infants. Phenylalanine was converted to tyrosine at substantial rates in both extremely premature and term infants; however, this conversion rate was significantly higher (P < 0.05) in extremely premature infants during both the basal and parenteral nutrition periods. These data provide clear evidence that there is no immaturity in the phenylalanine hydroxylation pathway. Furthermore, although parenteral nutrition appears to produce similar increases in protein synthesis in extremely premature and term infants, proteolysis is suppressed much less in extremely premature newborns. The factors responsible for this apparent resistance to suppression of proteolysis in the very immature newborn remain to be elucidated.

Original languageEnglish (US)
Pages (from-to)746-754
Number of pages9
JournalJournal of Clinical Investigation
Issue number3
StatePublished - Feb 1 1996


  • leucine
  • phenylalanine
  • protein synthesis
  • protein turnover
  • stable isotope tracers

ASJC Scopus subject areas

  • Medicine(all)

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