Regulation of ammonia-metabolizing enzymes expression in the liver of obese rats: differences between genetic and nutritional obesities.
OBJECTIVE
To determine the expression of carbamoylphosphate synthetase (CPS) and glutamine synthetase (GS) in two different models of obese rats: genetically obese rats and diet obese rats.


METHODS
Lean and genetically obese (fa/fa) Zucker rats were used.


METHODS
Lean animals (30-60 d old) were fed for 30 d with standard chow pellets or with a hypercaloric cafeteria diet. Genetically obese rats were fed with standard chow pellets.


METHODS
Enzyme activity, protein (Western blot) and mRNA (Northern blot) contents of CPS and GS were measured in liver homogenates.


RESULTS
In genetically obese animals CPS mRNA content was higher, and GS mRNA content was lower than in control animals; CPS protein content did not change and CPS activity was lower than in control rats. Diet-obese rats had higher levels of CPS and GS mRNAs than control animals; GS protein content and activity was higher than in the control group and at the same time, CPS activity was very low.


CONCLUSIONS
In the genetically obese animals the expression of CPS and GS is mainly regulated at the pre-translational level, whereas in the diet obese rats there is a noticeable post-translational component. A reciprocal regulation between CPS and GS can be established at pre-translational levels, whereas at post-transcriptional levels it cannot. It can be concluded that in diet-obese animals the mechanisms involved in retaining nitrogen (low CPS activity) are modulated at the post-translational level.
Roig
R
R
Department de Bioquímica i Biotecnologia, Facultat de Química, Universitat Rovira i Virgili, Tarragona, Spain.
Esteve
M
M
Remesar
X
X
Lamers
W H
WH
Arola
L
L
Salvadó
J
J
D000641:Ammonia / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D015152:Blotting, Northern / Q000379:methods; D015153:Blotting, Western / Q000379:methods; D002222:Carbamoyl-Phosphate Synthase (Ammonia) / Q000235:genetics / Q000378:metabolism; D015331:Cohort Studies; D015971:Gene Expression Regulation, Enzymologic; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000201:enzymology*; D008297:Male; D009584:Nitrogen / Q000378:metabolism; D009765:Obesity / Q000201:enzymology* / Q000235:genetics; D016017:Odds Ratio; D044343:Overnutrition; D012313:RNA / Q000032:analysis; D051381:Rats; D011924:Rats, Zucker; D012189:Retrospective Studies
D012313:RNA; D000641:Ammonia; D005974:Glutamate-Ammonia Ligase; D002222:Carbamoyl-Phosphate Synthase (Ammonia); D009584:Nitrogen