Effects of peritoneal injection of NH4HCO3 on nitrogen excretion and metabolism in the swamp eelmonopterus albus? increased ammonia excretion with an induction of glutamine synthetase activity

Abstract

Monopterus albus has to deal with high environmental ammonia concentrations during dry seasons and agricultural fertilization in rice fields. In this study, NH₄HCO₃ (10 μmol per g fish) was injected into the peritoneal cavity of M. albus, raising the level of ammonia in the body, in order to elucidate the strategies involved in defense against the toxicity of exogenous ammonia. During the subsequent 24 h after NH₄HCO₃ injection, there was a significant increase in the ammonia excretion rate, which indicates that the main strategy adopted by M. albus was to remove the majority of the exogenous ammonia through enhanced ammonia excretion. Exogenous ammonia was not detoxified into urea for excretion or accumulation. Six hours post‐injection of NH₄HCO₃, ammonia content in the tissues built up significantly, especially in the brain, which suggests that M. albus had high tolerance of ammonia toxicity at the cellular and sub‐cellular levels. By hour 12 post‐injection, there were significant increases in the activities of glutamine synthetase in the muscle, liver, and gut, accompanied by significant increases in glutamine contents in the muscle and the liver. There was also a significant increase in the glutamine content in the brain at hour 6 post‐injection of NH₄HCO₃. These results confirm the capability of M. albus to detoxify ammonia through glutamine synthesis. Overall, injection of NH₄HCO₃ had only minor effects on the contents of FAAs, other than glutamine, in tissues of M. albus because the majority (70%) of the injected ammonia was excreted within the 24–h period. J. Exp. Zool. 301A:324–333, 2004.