Effects of crowding on ornithine-urea cycle enzyme mRNA expression and activity in gulf toadfish (Opsanus beta)

Tammy Laberge, Patrick J. Walsh, M. Danielle McDonald

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)2394-2402
Number of pages9
JournalJournal of Experimental Biology
Issue number15
StatePublished - Aug 1 2009


  • Ammonia
  • Arginase
  • Argininosuccinate lyase
  • Argininosuccinate synthetase
  • Carbamoyl phosphate synthetase
  • Cortisol
  • Glutamine synthetase
  • Liver
  • Nitrogen metabolism
  • Ornithine carbamoyl transferase
  • Transcription
  • Urea

ASJC Scopus subject areas

  • Animal Science and Zoology
  • Ecology, Evolution, Behavior and Systematics
  • Molecular Biology
  • Physiology
  • Insect Science
  • Aquatic Science


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