PMID: 16843938Aug 1, 1995Paper

Urea kinetics: effect of severely restricted dietary intakes on urea hydrolysis

Clinical Nutrition : Official Journal of the European Society of Parenteral and Enteral Nutrition
J M HibbertC Persaud

Abstract

Urea kinetics (urea-N production-P, excretion-E, hydrolysis-H, recycling-R and retention-S) were measured in 7 healthy adults consuming a standard diet compared with 4 fasted for 24 and/or 96 h, using primed/intermittent doses of [(15)N (15)N]-urea and mass spectrometry. Standard values were P = 196, E = 132, H = 65, R = 13 and S = 51, mgN/kg/day. After 24 h fasting all urea kinetics were reduced, and P and H were significantly reduced compared with the standard diet (p < 0.01 and < 0.05 respectively). After 96 h fasting, urea kinetics returned to standard values (P = 187, E = 136, H = 51, R =13 and S = 38, mgN/kg/day), although nitrogen intake was significantly lower (p < 0.001). Relative urea excretion (E/P) was 67%, standard diet, and 75% after fasting. Consequently H/P was slightly reduced from 33 to 25%. S/P was 26%, standard diet, 15% after 24 h and 20% after 96 h fasting, suggesting increased urea-N retention with prolonged fasting. These results imply a slight temporary shift towards increased nitrogen excretion at 24 h and subsequent return to the kinetics of the fed state after 96 h. Urea-N retention increases with prolonged fasting.

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Citations

Jun 1, 1999·Nutrition Research Reviews·J C Waterlow
Oct 12, 2019·American Journal of Physiology. Gastrointestinal and Liver Physiology·Jack E C KroneDaniel A Columbus
May 16, 2002·American Journal of Physiology. Regulatory, Integrative and Comparative Physiology·Michael A Singer

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