Fenitrothion‐induced alterations in ammonia metabolism in the crab, Oziotelphusa senex senex fabricius

AbstractFresh water crabs, (Oziotelphusa senex senex) were subjected to short‐term (1 day) and long‐term (30 days) exposure to a sublethal concentration of fenitrothion (0.04 mg litre‐1), and the hepatopancreatic nitrogen metabolism was investigated. Differential patterns of nitrogen metabolism were observed in the hepatopancreas in response to both short‐term and long‐term exposure. Levels of ammonia in hemolymph of crab after short‐term exposure were markedly increased, with an increase in excretion of ammonia. The activity levels of aspartate aminotransaminase (AAT), alanine aminotransaminase (AIAT) and glutamate dehydrogenase (GDH) were found to increase in the hepatopancreas during short‐term exposure, which suggests increased transamination and deamination of amino acids. The AMP‐deaminase activity increased in the hepatopancreas during short‐term exposure indicating increased deamination of nucleic acids. The activity levels of ornithine cycle enzymes such as arginino succinate synthetase (ArSS) and arginase indicated diminished activities resulting in a low level of operation of the urea cycle and consequent accumulation of ammonia during short‐term exposure. The whole view of ammonia production and utilization mechanisms suggests the probable synergistic manifestation of ammonia toxicity during short‐term fenitrothion poisoning.However, during long‐term exposure, the haemolymph had a low ammonia level. The excretion of ammonia was also found to decrease. The activity levels of AAT, AIAT and GDH in the hepatopancreas were found to increase. In contrast to these, the AMP‐deaminase activity decreased in the hepatopancreas suggesting decreased deamination of nucleic acids. ArSS and arginase activities increased indicating active operation of the urea cycle and consequent accumulation of urea. Glutamine synthetase activity rose with the accumulation of glutamine which may help in averting toxic effects of ammonia. The possible effects of fenitrothion toxicity on energy requirements, transdeamination patterns, ureogenesis and glutamine production have been discussed.