S F Chew

..squamosa...

..Our results indicate that a reduction in ammonia production and decreases in hepatic arginine and cranial tryptophan contents are important facets of aestivation in P. dolloi...

..anguillicaudatus uses partial amino acid catabolism to fuel its short period of activities on land and switches to the formation of glutamine to detoxify internally produced ammonia when it remains relatively inactive in the mud...

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..dolloi was adapted to synthesizing and excreting urea for the purpose of ammonia detoxification...

..Such a capability, together with modifications in gill morphology and morphometry as in P. schlosseri, might be essential to the development of an effective mechanism for the active excretion of NH+4...

..albus. This might explain why M. albus is able to estivate in mud for long periods (40 d) but can survive in air for only <10 d...

..Taken together, these results indicate that H. signifer in freshwater could be confronted with postprandial osmotic stress because of its capacity of conserving N and increasing urea synthesis upon feeding...

..dolloi possesses transporters that facilitate the excretion of urea in water...

..boddaerti during the early phase of cyanide exposure...

..sinensis. After feeding, a slight but significant increase in the glutamine content occurred in the brain at hour 24, indicating that the brain might experience a transient increase in ammonia and ammonia was detoxified to glutamine...

..testudineus as an energy source to support locomotor activity during emersion. As a result, it is capable of wandering long distance on land from one water body to another as reported in the literature...

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..Instead, MSO affected activities of glutamate dehydrogenase and alanine aminotransferase and suppressed the rate of ammonia build up in the brain of fish injected with a lethal dose of CH(3)COONH(4)...

..signifer. Taken together, these results suggest that the primary function of the ornithine-urea cycle in ureogenic marine and freshwater elasmobranchs is to synthesize urea for osmotic water retention and not for ammonia detoxification...

..In conclusion, our results suggest that P. dolloi could respond to increases in salinity and changes in ionic composition in the external medium by suppressing ammonia production in preparation for aestivation when the water dries up...

..Only 4.6% of the exogenous ammonia was detoxified to urea. The glutamate contents in the muscle and liver also increased significantly, but the glutamine contents remained unchanged...

..Thus, it can be concluded that there are major differences in mechanisms of chronic and acute ammonia toxicity between brains of these two mudskippers and mammalian brains...

..These results suggest that urea excretion in P. dolloi is likely to be regulated by the level of internal ammonia in its body...

..Hence, it can be concluded that the juvenile axolotl acquired ureotelism while submerged in water, and its hepatic capacity of urea synthesis was more than adequate to handle the toxicity of endogenous ammonia during migration to land...

..albus in the mud for longer periods during drought because ammonia and glutamine concentrations had already built up to high levels in the body of specimens exposed to air for 144 h...

..signifier in 20 per thousand water. Therefore, H. signifer appears to have reduced its capacity to retain urea in order to survive in the freshwater environment and, consequently, it could not survive well in full-strength seawater...

..Our results suggest that such a strategy began to develop in those elasmobranchs, e.g. H. signifer, that migrate into a freshwater environment from the sea but not in those permanently adapted to a freshwater environment...

..0) for 6 days. These changes might lead to an even lower permeability to NH(3) in the skin, and reduced back diffusion of the actively excreted NH(4)(+) as NH(3) or the net influx of exogenous NH(3), under such conditions...

..These results represent the first report on a freshwater fish (C. gariepinus) adopting active excretion of ammonia (probably NH4+) as a major strategy to defend against ammonia toxicity when exposed to environmental ammonia...

..schlosseri throughout the 24 h period post-feeding, accompanied by a significant decrease in brain glutamine content between 12 h and 24 h...

..albus was suppressed in order to prevent the newly established internal steady state concentration of ammonia from rising to an intolerable level after an extended period of exposure to HEA...

..boddaerti detoxified sulfide mainly to sulfane sulfur in hypoxia. In conclusion, B. boddaerti was able to activate different mechanisms to detoxify sulfide, producing different types of detoxification products in normoxia and hypoxia...

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..Consequently, fish aestivating in mud had a lower dependency on increased urea synthesis to detoxify ammonia, which is energy intensive, than fish aestivating in air...