Minimal sampling protocol for accurate estimation of urea production: a study with oral [13C]urea in fed and fasted piglets.
OBJECTIVE
An oral [13C]urea protocol may provide a simple method for measurement of urea production. The validity of single pool calculations in relation to a reduced sampling protocol was assessed.


METHODS
In eight fed and five fasted piglets, plasma urea enrichments from a 10 h sampling protocol were measured following an intragastric [13C]urea bolus. Blood [13C]bicarbonate was measured to trace gut [13C]urea oxidation. Two-compartment and regression (single pool) computations were performed. Pool sizes were compared to urea distribution over total body water (TBW). Shorter protocol duration was tested in regression simulations.


RESULTS
Differences in urea kinetics between fed and fasted piglets did not reach statistical significance. Mean (+/-SE) urea pool from TBW times plasma urea concentration was 2.2+/-0.16 mmol kg(-1). Two-compartment modelling yielded similar results for pool size (despite the oxidation of a small amount of urea tracer). Urea appearance rate was 306+/-18 micromol kg(-1)h(-1). Regression calculations overestimated urea appearance rate vs. compartmental model (P<0.05). When samples <2 h were discarded, results were comparable to compartmental calculations even if protocol length was 6 h (325+/-24 micromol kg(-1)h(-1), NS).


CONCLUSIONS
Regression calculations using plasma enrichments sampled between 2 and 6 h after oral [13C]urea administration provide accurate rates of urea production, and are not affected by tracer oxidation.
Oosterveld
Michiel J S
MJ
Department of Paediatrics, VU University Medical Center, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands. mjs.oosterveld@vumc.nl
Gemke
Reinoud J B J
RJ
Dainty
Jack R
JR
Kulik
Willem
W
Jakobs
Cornelis
C
de Meer
Kees
K
D000284:Administration, Oral; D000818:Animals; D001834:Body Water / Q000378:metabolism; D002247:Carbon Isotopes; D005069:Evaluation Studies as Topic; D005215:Fasting; D006801:Humans; D007553:Isotope Labeling; D023421:Models, Animal; D010084:Oxidation-Reduction; D012680:Sensitivity and Specificity; D013552:Swine; D014508:Urea / Q000097:blood / Q000493:pharmacokinetics*
D002247:Carbon Isotopes; D014508:Urea