Detoxification Pathways in Response to Environmental Ammonia Exposure of the Cuttlefish, Sepia pharaonis: Glutamine and Urea Formation

To investigate the ammonia detoxification pathways of the cuttlefish, Sepia pharaonis, the effects of environmental ammonia nitrogen exposure (control, 1, 3, and 6 mg/L) on nitrogen metabolism were quantified in the hemolymph, liver, and gills. The levels of glutamine synthetase, glutamate dehydrogenase, and arginase activities and ammonia, glutamine, and urea concentrations in the hemolymph, liver, and gills significantly increased upon exposure to 3 and 6 mg/L ammonia nitrogen and exhibited a dose-dependent relationship with the ammonia exposure concentration. These results suggest two main pathways of metabolic ammonia detoxification in S. pharaonis exposed to ammonia in this study: (1) conversion of ammonia to urea, which is stored temporarily or excreted, via the ornithine-urea cycle and (2) conversion of ammonia to glutamine, which can be stored in the body or used for other anabolic processes.