Altered partition of threonine metabolism in pigs by protein-free feeding or starvation.
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a decrease of Thr oxidation and that the partition through these pathways was only altered when energy was completely withdrawn.
Ballèvre
O
O
Laboratoire d'Etudes du Métabolisme Azoté, Institut National de la Recherche Agronomique (INRA), Theix, Ceyrat, France.
Houlier
M L
ML
Prugnaud
J
J
Bayle
G
G
Bercovici
D
D
Seve
B
B
Arnal
M
M
D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000596:Amino Acids / Q000097:blood / Q000378:metabolism; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D001835:Body Weight; D004044:Dietary Proteins / Q000008:administration & dosage*; D005260:Female; D006728:Hormones / Q000097:blood; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D009929:Organ Size; D010084:Oxidation-Reduction; D013217:Starvation / Q000378:metabolism*; D013552:Swine; D013912:Threonine / Q000378:metabolism*; D013913:Threonine Dehydratase / Q000378:metabolism
D000596:Amino Acids; D001786:Blood Glucose; D004044:Dietary Proteins; D006728:Hormones; D013912:Threonine; D000429:Alcohol Oxidoreductases; C023159:L-threonine 3-dehydrogenase; D013913:Threonine Dehydratase