title: The non-invasive measurement of urea kinetics in normal man by a constant infusion of 15N15N-urea.
abstract: A two-pool model is described for the non-invasive measurement of urea kinetics in man. The isotope, 15N15N-urea, was given until an isotopic steady state was reached in urine and the time taken to achieve this is defined. During an isotopic steady state, a comparison was made of the effect of giving the isotope orally, intravenously and intragastrically; no differences were found between the different routes. Measurements of enrichment were made on excretion products in urine. In six normal adults with a protein intake of 200 mg N/kg/d, the urea production rate was 139 +/- 15 mg N/kg/d, 70 per cent of which was excreted in urine. Of the 34 mg N/kg/d produced by hydrolysis of urea in the gastrointestinal tract, 41 per cent was resynthesized to urea, and about 48 per cent was available for other synthetic processes.
mesh_terms: D000328:Adult; D004064:Digestive System / Q000378:metabolism; D006801:Humans; D007441:Intubation, Gastrointestinal; D007700:Kinetics; D008297:Male; D013058:Mass Spectrometry; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes; D014508:Urea / Q000008:administration & dosage / Q000378:metabolism* / Q000652:urine
chemical_list: D009587:Nitrogen Isotopes; D014508:Urea; D009584:Nitrogen