Journal ArticleDOI
The Little Skate Raja erinacea Exhibits an Extrahepatic Ornithine Urea Cycle in the Muscle and Modulates Nitrogen Metabolism during Low‐Salinity Challenge
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TLDR
Data suggest that a functional OUC may be present in the skeletal muscle tissues of R. erinacea and that enhanced urea excretion rates and the downregulation of the anchor OUC enzyme, arginase, in the liver may be critical in regulating tissue urea content under dilute‐seawater stress.Abstract:
Urea synthesis via the hepatic ornithine urea cycle (OUC) has been well described in elasmobranchs, but it is unknown whether OUC enzymes are also present in extrahepatic tissues. Muscle and liver urea, trimethylamine oxide (TMAO), and other organic osmolytes, as well as selected OUC enzymes (carbamoyl phosphate synthetase III, ornithine transcarbamoylase, arginase, and the accessory enzyme glutamine synthetase), were measured in adult little skates (Raja erinacea) exposed to 100% or 75% seawater for 5 d. Activities of all four OUC enzymes were detected in the muscle. There were no changes in muscle OUC activities in skates exposed to 75% seawater; however, arginase activity was significantly lower in the liver, compared to controls. Urea, TMAO, and several other osmolytes were significantly lower in the muscle of little skates exposed to 75% seawater, whereas only glycerophosphorylcholine was significantly lower in the liver. Urea excretion rates were twofold higher in skates exposed to 75% seaw...read more
Citations
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Journal ArticleDOI
Ammonia production, excretion, toxicity, and defense in fish: a review.
Yuen K. Ip,Shit F. Chew +1 more
TL;DR: This review focuses on both the earlier literature and the up-to-date information on the problems and mechanisms concerning the permeation of ammonia across mitochondrial membranes, the blood–brain barrier, the plasmalemma of neurons, and the branchial and cutaneous epithelia of fish.
Journal ArticleDOI
Stable isotope dynamics in elasmobranch fishes
John M. Logan,Molly Lutcavage +1 more
TL;DR: Nitrogen stable isotope values of skate blood and skate and dogfish white muscle were not affected by tissue urea content, suggesting that available diet–tissue discrimination estimates for teleost fishes with similar physiologies would provide accurate estimates for elasmobranchs.
Journal ArticleDOI
The unusual energy metabolism of elasmobranch fishes.
TL;DR: In this article, the authors assess hypotheses for the evolution of the unusual energy metabolism of elasmobranchs and propose that the need to synthesize urea has influenced the utilization of ketone bodies and amino acids as oxidative fuels.
Journal ArticleDOI
The dogfish shark (Squalus acanthias) increases both hepatic and extrahepatic ornithine urea cycle enzyme activities for nitrogen conservation after feeding.
Makiko Kajimura,Patrick J. Walsh,Patrick J. Walsh,Thomas P. Mommsen,Thomas P. Mommsen,Chris M. Wood,Chris M. Wood,Chris M. Wood +7 more
TL;DR: It is suggested that N conservation is a high priority in this elasmobranch and that feeding promotes ureogenesis and growth.
Journal ArticleDOI
Excretory nitrogen metabolism and defence against ammonia toxicity in air-breathing fishes.
Shit F. Chew,Yuen K. Ip +1 more
TL;DR: The responses of air-breathing fishes to ameliorate ammonia toxicity are many and varied, determined by the behaviour of the species and the nature of the environment in which it lives.
References
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Book
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TL;DR: This volume discusses water-Solute Adaptations: The Evolution and Regulation of the Internal Milieu, and the influence of Oxygen Availability on the Diving Response and Its Evolution.
Journal ArticleDOI
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A. Garcia-Perez,Maurice B. Burg +1 more
TL;DR: Normal organic osmolyte regulation contributes to the survival and growth of medullary cells in their hyperosmolal environment, and defective regulation can damage them.
Journal ArticleDOI
Improvements in the determination of urea using diacetyl monoxime; methods with and without deproteinisation
TL;DR: The sensitivity of the colorimetric reaction and stability of the colour are enhanced over existing related procedures and the serum blank diminished, enabling urea to be precisely measured in micro amounts (1--5 microliters) of serum.
Journal ArticleDOI
An optimal manual procedure for ammonia analysis in natural waters by the indophenol blue method
Ingrid Ivančić,Danilo Degobbis +1 more
TL;DR: In this article, the colorimetric indophenol blue method was used for ammonia determination in natural waters by Solorzano's procedure, with phenol-alcohol, nitro-prusside, alkaline citrate and hypochlorite as reagents, was shown to be appropriate for routine work.
Journal ArticleDOI
The retention and physiological role of urea in the elasmobranchii
TL;DR: The high urea content (2·0 and 2·5 per cent.) that characterises the blood, body fluids and tissues of the Elasmobranchii owes its origin to the relative impermeability of the gills and integument to this substance.