Protein Turnover Rates in Sick, Premature Neonates during the First Few Days of Life

Mitton, Sally G.; Calder, Andrew A.; Garlick, Peter J.

doi:10.1203/00006450-199111000-00005

Cited by 50 publications

(24 citation statements)

References 22 publications

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“…Keeping this qualification in mind, the data are consistent with the notion that the ability to increase whole body protein synthesis in response to intravenous nutrition is relatively independent of the stage of development. Further support of this concept is provided by two previous studies in premature infants; these studies have also suggested that intravenous nutrition may result in increased protein synthesis as reflected by leucine kinetics (32,33).…”

Section: Discussionmentioning

confidence: 57%

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

Denne¹,

Karn²,

Ahlrichs³

et al. 1996

J. Clin. Invest.

110

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To determine to what extent intravenous nutrition can reduce proteolysis 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 during parenteral nutrition in clinically stable, extremely premature ( ‫ف‬ 26 wk of gestation) infants and in normal term newborns. In response to parenteral nutrition, there was significantly less suppression ( P Ͻ 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 Ͻ 0.01) and by the same magnitude ( ‫ف‬ 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 Ͻ 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.

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Section: Discussionmentioning

confidence: 57%

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

Denne¹,

Karn²,

Ahlrichs³

et al. 1996

J. Clin. Invest.

110

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“…They estimated the total obligatory N loss to be 145 mg. kg-' .d-I or 0.9 g protein kg-lad-', a rate similar to the measurements in the present study. Estimates of protein oxidation in full-term infants using [I-"C]leucine by us were -1.4 g1kg.d-', which is much higher than that in the present study (4,5,19,20). These differences may be related to the KALHAN observation that urea cycle enzymes can be readily regulated to conserve N. Furthermore, differences between protein oxidation measured by leucine tracer and that measured by urea excretion have also been observed under other physiologic circumstances.…”

Section: Urea Synthesis In Newborn Infantscontrasting

confidence: 49%

“…In addition, it does not include nonurinary losses of N, e.g. skin and gut, does not include loss of urea as a result of hydrolysis in the gut (if any), and requires adjustments for the change in body urea pool size (4,5,20). The tracer carbon oxidation method also has the disadvantage of requiring the accurate measurement of the rate of carbon dioxide production, estimation of bicarbonate retention, and the effect of exchange of tracer carbon, resulting in a loss of tracer.…”

Section: Discussionmentioning

confidence: 99%

Rates of Urea Synthesis in the Human Newborn: Effect of Maternal Diabetes and Small Size for Gestational Age

Kalhan

1993

Pediatr Res

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ABSTRACT. The rates of urea synthesis and glucose turnover were quantified during fasting using ["N2]urea and [6,62H2]glucose tracers with the prime constant rate infusion technique in 33 infants: 19 normal infants, 10 infants of diabetic mothers (IDM), and four small for gestational age (SGA) infants born at term gestation. All infants were studied during fasting 4 h after their last feed. Eleven normal infants and six IDM were studied soon after birth before any feeding. The rate of urea synthesis in normal infants was 5.84 + 2.0 mg of nitrogen (N)/kg* h-' or 3.5 rmol of urea/kg*min-'. The rate was slightly higher in IDM (7.09 + 3.0 mg N/kg-h-') and lower in SGA infants (4.59 f 1.22 mg N/kg-h-'); however, the differences were not statistically significant. No differences in urea synthesis were observed between infants studied soon after birth and those studied after initiation of feeding. The rate of appearance of glucose was lower in IDM infants studied during the first 6 h after birth (IDM 19.62 f 2.14 rmol/kg*min-', normal infants 24.03 f 4.05 rmol/ kgwmin-I, p = 0.01). However, rate of appearance of glucose in IDM infants studied between 17 and 20 h after birth was similar to that in normal infants. Rate of appearance of glucose was lower (not significantly) in SGA infants (17.7 f 3.3 pmol/kg*min-') as compared with normal infants. No correlation between rates of urea synthesis and glucose turnover was observed. These data show that newborn infants during fasting have an obligatory rate of protein oxidation of -0.87 g/kg*d-' and that maternal diabetes has no effect on it. The slightly lower rate of protein oxidation in SGA infants may be related to increased N assimilation. (Pediatr Res 34: 801-804, 1993) Abbreviations N, nitrogen IDM, infants of insulin-dependent diabetic mothers SGA, small for gestational age AGA, appropriate for gestational age Ra, rate of appearance Measurements of urea N excretion are performed to quantify nitrogen balance and rates of protein oxidation in infants and children. However, limited data are published in literature on the rates of urea synthesis or excretion in the human newborn. Previous data suggested that the rates of urea N excretion in the newborn infant may be much lower than those in the adults as (2) showed that the rates of urea N excretion in the urine of newborn infants were higher than previously suggested. Nevertheless, the urea excretion rate was much less than that estimated for the human fetus at term gestation by Gresham et al. (3). Inasmuch as urinary urea does not reflect the excretion of the total urea synthesized because of loss of urea by skin and possibly because of hydrolysis in the gut, the measurements of urea N excretion in urine will underestimate the actual rates of urea synthesis and therefore protein oxidation (4, 5). In fact, the rates of protein oxidation, as measured by oxidation rates of essential amino acids such as leucine (6, 7), suggest a much higher rate of protein oxidation in full-term newborn infants (-1.4 g/kg. d-I) as compar...

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“…The different tracers give different results, i.e. for whole-body protein synthesis, rates ranging from 5 g.kg-l.d-' to 26 g.kg-'.d-' have been reported, depending on clinical and experimental conditions (3,14). Studies were performed comparing different tracers and amino acids in adults (18) and in term infants (19) or comparing different amino acids with a similar label (8,9,20).…”

mentioning

confidence: 99%

“…(Pediatr Res 37: 381-388, 1995) Abbreviations AGA, appropriate for gestational age SGA, small for gestational age KICA, ketoisocaproic acid IRMS, isotopic ratio mass spectrometer quantification of protein metabolism by measurement of isotope enrichment in an end product of protein catabolism in urine (3)(4)(5)(6)(7)(8)(9)(10). [1 -l"]~eucine, another stable isotopic labeled tracer, has been used for protein studies in preterm neonates more recently, with either the measurement of isotopic enrichment of [l-13~]leucine or [ ' 3~]~-~~~~ in urine (11,12) or plasma (13)(14)(15)(16)(17). The different tracers give different results, i.e.…”

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confidence: 99%

Whole-Body Protein Turnover in Preterm Appropriate for Gestational Age and Small for Gestational Age Infants: Comparison of [15N]Glycine and [1-13C]Leucine Administered Simultaneously

Goudoever

Sulkers

Halliday³

et al. 1995

Pediatr Res

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Measurements of whole-body protein turnover in preterm infants have been made using different stable isotope methods. Large variation in results has been found, which could be due to different clinical conditions and/or the use of different tracers. We studied 14 appropriate for gestational age and nine small for gestational age orally fed preterm infants using ['"]glycine and [l-"C]leucine simultaneously, which allowed us to make a comparison of commonly used methods to calculate whole-body protein turnover. Whole-body protein turnover was calculated from '% enrichment in urinary ammonia and urea after [I5N]-glycine administration and from the "C enrichment in expired CO, after administration of [l-'"]leucine.Enrichment of a-ketoisocaproic acid after [l -l"]leucine constant infusion was measured as a direct parameter of whole-body protein turnover. Group means for whole-body protein turnover using ['5N]glycine or [l-13C]leucine ranged from 10 to 14 g.kgP'.dP1, except when using the end product method that assumes a correlation The use of stable isotopes for measuring metabolic processes in vivo has a clear ethical advantage over radioactive isotopes. The nonradioactive character allows their use in pregnancy and in infants. Schoenheimer et al.(1) used stable isotopes to study protein turnover as early as 1939, but more extensive research has been done since the 1970s, when analytical techniques improved remarkably (2). From then onward, numerous protein turnover studies have been performed using stable isotopes, in adults as well as in children. 15~-labeled amino acids have been favored for many years in preterm infants because of the noninvasive character of the studies. The method allows

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Protein Turnover Rates in Sick, Premature Neonates during the First Few Days of Life

Cited by 50 publications

References 22 publications

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

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

Rates of Urea Synthesis in the Human Newborn: Effect of Maternal Diabetes and Small Size for Gestational Age

Whole-Body Protein Turnover in Preterm Appropriate for Gestational Age and Small for Gestational Age Infants: Comparison of [15N]Glycine and [1-13C]Leucine Administered Simultaneously

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