Tracer methods underestimate short-term variations in urea production in humans

The American Journal of Physiology
M J Hamadeh, L J Hoffer

Abstract

Urea production rate (Ra) is commonly measured using a primed continuous tracer urea infusion, but the accuracy of this method has not been clearly established in humans. We used intravenous infusions of unlabeled urea to assess the accuracy of this technique in normal, postabsorptive men under the following four different conditions: 1) tracer [13C]urea was infused under basal conditions for 12 h (control); 2) tracer [13C]urea was infused for 12 h, and unlabeled urea was infused from hours 4 to 12 at a rate twofold greater than the endogenous Ra ("step" infusion); 3) tracer [13C]urea was infused for 12 h, and unlabeled urea was infused from hours 4 to 8 ("pulse" infusion); and 4) tracer [13C]urea was infused for 9 h, and unlabeled alanine was infused at a rate of 120 mg.kg-1.h-1 (1.35 mmol.kg-1.h-1) from hours 4 to 9. Urea Ra was calculated using the isotopic steady-state equation (tracer infusion rate/tracer-to-tracee ratio), Steele's non-steady-state equation, and urinary urea excretion corrected for changes in total body urea. For each subject, endogenous urea Ra was measured at hour 4 of the basal condition, and the sum of this rate plus exogenous urea input was considered as "true urea input". Under control conditions, ur...Continue Reading

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Citations

Mar 11, 2000·American Journal of Physiology. Endocrinology and Metabolism·D YangH Brunengraber
Jun 12, 2003·American Journal of Physiology. Endocrinology and Metabolism·Helene NørrelundNiels Møller
Aug 25, 2007·American Journal of Physiology. Gastrointestinal and Liver Physiology·Marcel C G van de PollCornelis H C Dejong
Oct 28, 2004·American Journal of Physiology. Endocrinology and Metabolism·Cécile BosDaniel Tomé
Jul 7, 2001·American Journal of Physiology. Endocrinology and Metabolism·M J Hamadeh, L J Hoffer
May 15, 2001·American Journal of Physiology. Endocrinology and Metabolism·M J Hamadeh, L J Hoffer
Jul 7, 2001·American Journal of Physiology. Endocrinology and Metabolism·M J HamadehL J Hoffer
Aug 19, 2000·American Journal of Physiology. Endocrinology and Metabolism·M G KrishnaD H Wasserman
Oct 25, 2002·American Journal of Physiology. Endocrinology and Metabolism·Mazen J Hamadeh, L John Hoffer
Feb 9, 2010·Progress in Neurobiology·Daniel J WilkinsonPeter W Watt

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