期刊
JOURNAL OF EXPERIMENTAL BIOLOGY
卷 212, 期 15, 页码 2394-2402出版社
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jeb.030411
关键词
nitrogen metabolism; transcription; carbamoyl phosphate synthetase; glutamine synthetase; ornithine carbamoyl transferase; argininosuccinate synthetase; argininosuccinate lyase; arginase; urea; ammonia; liver; cortisol
类别
资金
- NSF [IOS- 0455904]
- NSERC
- Canada Research Chair Program
- Canada Foundation for Innovation
The gulf toadfish (Opsanus beta) is a facultatively ureotelic fish that excretes primarily urea under conditions of crowding or confinement. To examine the relationship between ammonia production, urea production and the ornithine-urea cycle (O-UC) enzyme activity and mRNA expression, we subjected toadfish to two-day and seven-day crowding regimes. Plasma cortisol levels were measured and liver tissue was assayed for ammonia and urea concentrations. Liver glutamine synthetase (GS), carbamoyl phosphate synthetase III (CPS), ornithine carbamoyl transferase (OCT) and arginase (ARG) activities were also measured. Quantitative PCR was utilized to determine liver GS, CPS, OCT, ARG, argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL) mRNA expression. Hepatic ammonia concentrations decreased with increased duration of crowding whereas liver urea and circulating cortisol levels increased. An elevation in enzyme activity with increased duration of crowding was observed for all four O-UC enzymes examined. By contrast, mRNA expression was variable for the O-UC enzymes and only CPS and ASS had mRNA expression levels that were elevated in crowded fish. These results suggest that the activities of O-UC enzymes are better predictors for urea production than O-UC enzyme mRNA expression levels.
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