title: Urea production and recycling in neonates.
abstract: Urea represents 15% of the nitrogen in breast milk, but its functional significance is unclear. We have proposed that the urea may be utilised as a valuable source of nitrogen in neonates. We report the first measurements of urea kinetics in newborn, full-term infants. Six neonates received a continuous nasogastric infusion of 15N15N-urea over 24 hours. Urine was collected every 2 hours and the isotopic enrichment in urea was measured by mass spectrometry. Urea kinetics were calculated by the method of Jackson. The urea production rate was 17.3 mmol/kg/d (range, 15.6 to 19.2), but the urinary urea excretion rate, 3.5 mmol/kg/d (range, 1.2 to 4.9), was only 20% of production. Hence, 80% of urea produced was hydrolysed in the colon and the nitrogen made available for further metabolism. These data show that urinary urea excretion is a poor indication of urea production in the newborn and that there is substantial salvaging of urea nitrogen by the colon.
authors.affiliation: Wessex Regional Centre for Paediatric Surgery, Southampton General Hospital, England.
authors.forename: R A
authors.initials: RA
authors.lastname: Wheeler
authors.forename: A A
authors.initials: AA
authors.lastname: Jackson
authors.forename: D M
authors.initials: DM
authors.lastname: Griffiths
mesh_terms: D001835:Body Weight; D004750:Enteral Nutrition; D005865:Gestational Age; D006801:Humans; D007225:Infant Food; D007231:Infant, Newborn / Q000378:metabolism*; D009587:Nitrogen Isotopes; D014508:Urea / Q000378:metabolism* / Q000652:urine
chemical_list: D009587:Nitrogen Isotopes; D014508:Urea