This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to quantify the kinetics and metabolism of methionine (transsulfuration pathway), a sulfur containing essential amino acid, in healthy full term babies and in low birth weight infants. Healthy full term babies will be recruited from the normal newborn nursery while low birth weight (premature) infants will be recruited from the Neonatal Intensive Care Unit. By using stable, non-radioactive isotopic tracers of methionine, phenylalanine and urea, the investigators propose to quantify the kinetics of methionine and its relation to whole body protein breakdown (measured by phenylalanine Ra) and whole body rate of protein oxidation (measured by production of urea). In full term infants, after a three-hour basal study, the effect of enterally administered nutrients (formula) on the above parameters will be examined. The total duration of study will be seven hours: three hours basal and four hours of response to intermittent (every 30 minute) feeds. Respiratory calorimetry measurements will be done at periodic intervals in term infants. Blood samples from indwelling venous cannula will be drawn at periodic intervals. The LBW infants will be studied while they are receiving parenteral amino acid at 3.0 g/kg/d for at least 24 hours and not enterally fed. The studies are significant in that they will generate important data which may provide the rationale for supplementation (or not) of cysteine (sulfur amino acid, formed from methionine) in the newborn infant.
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