A CELL MODEL TO ASSESS PROTEIN SYNTHESIS AND AMINO ACID POOLS IN NEONATES

Abstract

The relation of protein synthesis (PS) to extracellular (EC) and intracellular (IC) amino acid (AA) pools, birthweight, gestational age and postnatal weight change in human neonates is unknown. Viable neutrophils isolated from 1-2 ml venous blood were used as a cell model to evaluate these relationships in 35 infants with complete data at 33 to 44 weeks postconceptual age (2d-14 weeks postnatal age), PS (3H-leucine incorp, p moles/hr/mg DNA) and 19 cell AA (n moles/mg DNA) were quantified in the leukocytes and 19 AAs in the same plasma (n moles/ml) (Dionex high pressure AA analyzer, fluorometric detection). No significant (p <.05) correlations were detected between PS and individual plasma AAs. PS was correlated with 11 of 19 IC AAs and with sets of both essential (ESSAA) and nonessential (NESSAA) IC AAs. PS also was inversely (−) correlated with birthwt., gest.age, postconceptual age and weight at time of study. When studied in a stepwise multiple regression of PS on the age-weight variables, weight at study was the only variable selected by the model and accounted for 20% (R2=.205, p=0.006) of the variance in PS. Of the AAs, the IC ESSA As were the only set explaining a significant proportion of the variance in PS (R2=0.274, p=0.001). Thus it appears that the smaller and more preterm the infant, the greater the rate of protein synthesis; which, in turn, is more closely related to levels of IC ESSA As than to plasma concentrations of the AAs. Measures of protein synthesis and IC AAs are feasible, even in neonates, and should contribute significantly to formulation and evaluation of therapies designed to improve these modalities.