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Estimation of allantoin flux using continuous infusion of [14C]allantoin: sensitivity to plasma loading with unlabelled allantoin

Published online by Cambridge University Press:  09 March 2007

L. P. Kahn ,
D. Ouellet  and
J. V. Nolan
L. P. Kahn*
Affiliation:
School of Rural Science and Natural Resources, University of New England, Armidale, NSW 2351, Australia
D. Ouellet
Affiliation:
Canada Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, Lennoxville, Quebec, Canada
J. V. Nolan
Affiliation:
School of Rural Science and Natural Resources, University of New England, Armidale, NSW 2351, Australia
*
*Corresponding author: Dr Lewis P. Khan, fax +61 2 67733275l, email kahn2@metz.une.edu.au
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Abstract

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Allantoin net flux through the plasma allantoin compartment was determined in sheep given a roughage diet by means of a continuous infusion of [4,5-14C]allantoin for 17 h. Unlabelled allantoin was infused intravenously during the last 7 h of the tracer infusion to increase the allantoin flux by approximately 75 %. When unlabelled allantoin was infused, the specific radioactivity of allantoin in plasma and urine declined exponentially to approach a lower plateau some 2–3 h later. The estimate of net flux during the infusion of unlabelled allantoin, estimated from blood plasma and urine, was on average 79 and 90 % of expected values. Expected values of allantoin net flux during infusion of unlabelled allantoin were calculated as the sum of allantoin net flux pre-loading plus the known rate of infusion of the allantoin load. It is probable that endogenous allantoin synthesis was decreased by the infusion of allantoin: allosteric inhibition of uricase appears a plausible explanation for this observation, and for lower estimates of net flux. Appearance of labelled allantoin-C in ruminal or blood bicarbonate was negligible. Our results indicate that net flux of allantoin through blood plasma is a good predictor of the entry rate of allantoin into the primary compartment and should be a better predictor of rumen microbial outflow than urinary allantoin excretion. However, measurements of allantoin-specific radioactivity, during continuous infusion, should be taken after a period of 24 h, at which time the true plateau specific radioactivity value of allantoin in plasma would be attained.

Keywords

AllantoinMicrobial nitrogenSheep
Type
Research Article
Information
British Journal of Nutrition , Volume 86 , Issue 6 , December 2001 , pp. 691 - 696
Copyright
Copyright © The Nutrition Society 2001

References

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