AJP - Endocrinology and Metabolism, Vol 260, Issue 4 E662-E668, Copyright © 1991 by American Physiological Society
Sarcosine kinetics in pigs by infusion of [1-14C]sarcosine: use for refining estimates of glycine and threonine kinetics
O. Ballevre, V. Buchan, W. D. Rees, M. F. Fuller and P. J. Garlick
Rowett Research Institute, Bucksburn, Aberdeen, United Kingdom.
To investigate in vivo the interconversion between glycine (Gly) and its
N-methyl product sarcosine (Sar), [1-13C]Gly and [1-14C]Sar were infused
into hourly fed pigs receiving diets with low- and high-threonine levels.
An open two-pool model was developed to calculate Sar demethylation (DM)
and Gly methylation (GM). During [1-14C]Sar infusion, intracellular Gly
specific radioactivities (SA) in the liver and kidney were higher than
plasma Gly SA, suggesting that demethylation of Sar occurred in those
tissues. DM estimated by using hippuric acid (HA) as the production pool
had a mean value of 1.55 mumol.kg-1.h-1, similar to the Sar production rate
(mean 1.85 mumol.kg-1.h-1). GM was undetectable (less than 0.5
mumol.kg-1.h-1). These results suggest that, in fed pigs, Sar is produced
mainly from choline catabolism and is degraded only to Gly in liver and
kidney. On the assumption that Sar degradation gave rise only to Gly, the
production rate of Gly (Gly PR) was calculated from [1-13C]Gly and
[1-14C]Sar infusions using either the primary pools (plasma Gly and HA,
respectively) or the secondary pools (HA and plasma Gly, respectively). The
results were explained by a liver-plasma Gly exchange model. The whole body
Gly irreversible loss, i.e., direct loss from plasma and liver, was
calculated from this model to be 832 +/- 58 mumol.kg-1.h-1, showing that
the estimation of Gly PR with [1-13C]Gly infusion and plasma Gly enrichment
(599 +/- 56 mumol.kg-1.h-1) was a significant underestimate of the true
value.(ABSTRACT TRUNCATED AT 250 WORDS)
