Nitrogen balance and protein turnover during the growth failure in newly born low-birth-weight infants

Abstract

Weight gain, nitrogen balance, protein turnover, and energy and protein intakes were measured during the first week of life of 14 low-birth-weight (LBW) infants, 5 small-for-gestational-age (SGA) infants and 9 appropriate-for-gestational-age (AGA) infants enterally fed at rates determined by the infants ability to assimilate feed. Mean gross intakes were 334 KJ and 1.75 g/kg protein; 4 infants were increasing and 10 were losing weight at rates proportional to gross energy and protein intakes and to nitrogen balance (0.031 g protein balance/g wt gain). Rates of protein synthesis and degradation measured by an intragastric infusion of [1-13C]leucine, averaged 14.5 and 15.9 g protein.kg-1.d-1, some 50% higher than previously reported in older preterm infants and not correlated with nitrogen balance. The growth failure of these infants was not associated with inadequate overall rates of protein turnover, but appeared to reflect an influence of the insufficient energy and protein intakes on the high rates of protein turnover, inducing changes in protein balance in either direction through relatively small changes in protein synthesis and/or degradation.

Arginine and nitric oxide metabolism in critically ill septic pediatric patients*

“…The rates of whole body protein turnover (synthesis and breakdown) were obtained assuming the leucine content of whole body mixed protein to be 621 mol/g of protein (48) and from nitrogen balance (g N·kg Ϫ1 ·day Ϫ1 ) (49).…”

Protein nutrition of the neonate

“…Unfortunately, at this stage the mechanism that mediates these apparently specific effects of colostrum is not known, although it appears that neither insulin nor insulin-like growth factor 1 are involved directly. Indeed, given the response in the central nervous system, it is tempting to speculate that the colostrum stimulation of protein synthesis is not a response to a soluble growth factor or hormone absorbed by the neonate, but that (1991,1992,1994,1995); Kandil et al (1991); Beaufrere et al (1992); van Goudoever et al (1995). || The 18-month-old children had recovered from malnutriton and were studied with [ 15 N]glycine.…”

Whole-body protein and amino acid turnover in man: What can we measure with confidence?

“…1. During a primed constant infusion the enrichment of the leucine in the free pool achieves a constant plateau value which can be measured in sampled plasma (or urine when plasma sampling is difficult as with preterm infants (De Benoist et al 1984: Kandil et al 1991). The advantage of leucine is that the enrichment of its a-keto acid (KIC) can be measured in the plasma, and since this must be derived from transamination of intracellular leucine it can be assumed to give a better estimate of the true precursor enrichment for both flux and oxidation.…”