Estimation of energy expenditure from the specific activity of
urinary urea during long-term subcutaneous infusion of nah14co3.
Elia, M, M G Jones, G Jennings, S D Poppitt, N J Fuller, P R
Murgatroyd & S A Jebb.
Dunn Clinical Nutrition Centre, Hills Road, Cambridge, CB2 2DH,
UK., Tel: (0223) 415619, Fax: (0223) 413763, Current address for M G
Jones: Dept of Chemical Pathology, Faculty of Medicine, The Chinese
University of Hong Kong
APStracts 2:0047E, 1995.
Five healthy male subjects were continuously infused subcutaneously
with 14C-bicarbonate (12.3[mu]Ci/day) using a minipump for 5 days
whilst in a whole body calorimeter. Energy expenditure was varied
over a range of 1.35 - 1.75 times basal metabolic rate. Urine
collections were obtained throughout the study and used to measure
the specific activity of urea, from which CO2 production was
estimated. It was assumed that the recovery of label in gaseous CO2
was 95% of that infused, and that the specific activity of urea was
85% of that of expired CO2. Continuous daily collections of
calorimeter air revealed that 95.6 +/- 1.3% (mean +/- SD) of infused
label was recovered as gaseous CO2, with little daily variation.
Another 1.5 +/- 0.4% was recovered as urinary urea. The estimated CO2
production, calculated from the specific activity of urea in 24h
urine samples corrected for the small effects due to changes in the
size and specific activity of the urea pool, was found to be 100 +/-
5% of the calorimeter estimate for 1 day periods (20.80 +/- 1.44 mol
CO2 /day), and 100 +/- 2% for 4 day periods. This study suggests that
in healthy subjects the labelled 14C-bicarbonate-urea method can
provide reasonable estimates of net CO2 production, over the range
examined.
Received 27 April 1994; accepted in final form 3 March 1995.
APS Manuscript Number E157-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.