Defensive strategies in response to environmental ammonia exposure of the sea cucumber Apostichopus japonicus: Glutamine and urea formation

Abstract The purpose of this study was to investigate ammonia detoxification strategies in the sea cucumber Apostichopus japonicus . In this study, A. japonicus was exposed to ammonia for 48 h at three different concentrations as 0, 0.5 and 1.25 mg L − 1 . Results showed that exposure to ammonia resulted in a large increase in ammonia concentration in the coelomic fluid. Glutamate dehydrogenase (GDH) activity, GDH relative mRNA expression, glutamine synthetase (GSase) activity, GSase relative mRNA expression, glutamine content, arginase (ARGase) activity, ARGase relative mRNA expression and urea content in the respiratory tree increased significantly and showed a pronounced time and dosage dependency. GDH, GSase activity, glutamine content, xanthine oxidase (XO) activity, ARGase activity and urea content in the body wall increased significantly but recovered to the control level within 48 h. The GSase activity and glutamine content did not recover and remained at an elevated level. Uric acid was not detected in all of the tissues during the investigation. The results suggest that protective strategies of glutamine formation and ureogenesis exist in A. japonicus , which could convert ammonia to non- or less toxic nitrogenous compounds on the exposure of ammonia. The detoxification level in the respiratory tree may be suitable to evaluate the toxicity of ammonia.