UREA PRODUCTION IN NORMAL BREAST-FED INFANTS MEASURED WITH PRIMED INTERMITTENT ORAL DOSES OF [N-15,N-15]UREA/

Urea kinetics were measured on 11 occasions in six normal, breast-fed infants aged 29-88 days. Prime and intermittent oral doses of [N-15, N -15]urea with measurement of enrichment of urea in urine were used. Th e rate at which urea appeared in the urea pool was 265 mg N/kg per hou r, 85% of which derived from endogenous production and 15% from the di et. Urinary excretion of urea was 87 mg N/kg per hour. Therefore, 60% of the urea entering the pool each day was hydrolysed by the metabolic activity of the colonic microflora and the nitrogen was made availabl e for further metabolic interaction. The rate of urea appearance and t he extent to which urea nitrogen was salvaged were greater in infants under 6 weeks than in those over 6 weeks, indicating that urea kinetic s is a more active process at an early age, and slows with time. With respect to factors influencing urea kinetics, the apparently conflicti ng results which have appeared in the literature may be explained. The results may help explain the growth of breast-fed infants on low prot ein intakes.