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Am J Physiol Endocrinol Metab 261: E748-E757, 1991;
0193-1849/91 $5.00
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AJP - Endocrinology and Metabolism, Vol 261, Issue 6 E748-E757, Copyright © 1991 by American Physiological Society

ARTICLES

Altered partition of threonine metabolism in pigs by protein-free feeding or starvation

O. Ballevre, M. L. Houlier, J. Prugnaud, G. Bayle, D. Bercovici, B. Seve and M. Arnal
Laboratoire d'Etudes du Metabolisme Azote, Institut National de la Recherche Agronomique (INRA), Theix, Ceyrat, France.

Kinetic aspects of threonine (Thr) metabolism were examined in growing pigs fed a well-balanced diet (C), an isocaloric protein-free diet (PF), or starved (S) for 48 h. With the use of continuous simultaneous infusion of L-[1-13C]Thr, [1-14C]sarcosine, and 2-[1-14C]ketobutyrate (KB) for 10 h, estimates were made of rates of Thr incorporated into protein (S), released from body proteins (B), and oxidized through the catabolic pathways of L-Thr 3-dehydrogenase (TDG) and threonine dehydratase (TDH). In the C group S was 185, B was 138, Thr disposal to glycine (DRThr-Gly) was 47, and Thr disposal to KB (DRThr-KB) was 7 mumol.h-1.kg-1. Consequently, Thr balance was +48 mumol.h-1.kg-1. In the PF-fed pigs, S, B, DRThr-Gly, and DRThr-KB were significantly reduced by 38, 15, 74, and 75%, respectively. In the S group, S, B, and DRThr-Gly were significantly reduced by 47, 17, and 55%, respectively, but DRThr-KB was similar to the C group. DRThr-Gly in all groups was highly correlated with TDG enzyme activity measured in liver homogenates. By contrast with in vivo results, TDH enzyme activity was increased by 88% (P less than 0.05) in the S group and decreased by 27% (not significant) in the PF group compared with the C group. The TDH pathway accounted for 13, 12, and 27% of total Thr oxidation in the C, PF, and S groups, respectively. These results suggest that Thr conservation in protein-depleted states (PF and S groups) occurred mainly by a decrease of Thr oxidation and that the partition through these pathways was only altered when energy was completely withdrawn.


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J. D. House, B. N. Hall, and J. T. Brosnan
Threonine metabolism in isolated rat hepatocytes
Am J Physiol Endocrinol Metab, December 1, 2001; 281(6): E1300 - E1307.
[Abstract] [Full Text] [PDF]


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