Urea Cycle Activity and Arginine Formation in Rainbow Trout (Salmo gairdneri)

Abstract

Studies were conducted to determine whether rainbow trout fingerlings possess the ability to synthesize arginine via the urea cycle. Several urea cycle enzymes were detected in trout tissues. An experiment was conducted to determine whether the enzymes increase in response to starvation or in response to dietary protein level (0, 30, 40, 50% protein). Although some effects were observed, they did not appear to be consistent with the function of the urea cycle as a mechanism of detoxifying ammonia in the fish. The activities of kidney arginase and liver and muscle carbamoyl phosphate synthetase (CPS) were higher (P less than 0.05) when protein was omitted from the diet (P less than 0.05) than when it was present but were unaffected by protein level otherwise. The activities of liver arginase and kidney and muscle CPS and ornithine transcarbamoylase (OTC) were higher (P less than 0.05) in starved fish than in fish that received adequate levels of protein. Liver CPS and OTC were lower in starved fish than in fish fed 30% protein. L-[l-14C]ornithine hydrochloride and L-[carbamoyl-14C]citrulline, injected intraperitoneally, were incorporated into tissue arginine, a finding consistent with arginine biosynthesis via the urea cycle. When one-half of dietary arginine was replaced by equimolar amounts of glutamic acid, ornithine or citrulline, glutamic acid markedly reduced growth (P less than 0.05), whereas growth was depressed only slightly by ornithine (P less than 0.05) and not depressed by citrulline (P greater than 0.05). We conclude that trout have a urea cycle that provides for potential arginine biosynthesis.

Dogmas and controversies in the handling of nitrogenous wastes:Expression of arginase Type I and II genes in rainbow trout: influence of fasting on liver enzyme activity and mRNA levels in juveniles

“…Chiu et al, 1986;Jürss et al, 1987). Although arginase activity per gram of liver tissue and per mg of liver protein significantly increased in fasted fish, if one considers enzyme activity per gram of fish, arginase activities are similar between fasted and fed fish (6·weeks).…”

“…Chiu et al, 1986;Jürss et al, 1987). We hypothesized that the two trout arginase genes would be differentially regulated in response to dietary manipulation.…”

“…In various teleost fishes, liver arginase activity is induced following several weeks of fasting (Chiu et al, 1986;Jürss et al, 1987;Singh and Singh, 1988;Wright, 1993). Increased arginase activity may be important in amino acid catabolism in fasting fish (Ballantyne, 2001;Wood, 2001).…”

“…Based on the similarity between Onmy-ARG01 and mammalian Type I arginase (hepatic OUC-related) and between Onmy-ARG02 and mammalian Type II arginase (nonhepatic), we hypothesized that only Onmy-ARG02 expression would be enhanced in the livers of fasted juvenile trout where the OUC is non-functional. We reproduced the protocol used by Chiu et al (1986), where juvenile trout were either fed or fasted for a 6-week period. Livers were collected at 0 and 6·weeks, and arginase activities, as well as Onmy-ARG01 and Onmy-ARG02 mRNA levels, were compared between fasted and fed fish.…”

Dietary arginine requirement for gibel carp (Carassis auratus gibelio var. CAS III) reduces with fish size from 50g to 150g associated with modulation of genes involved in TOR signaling pathway

“…Furthermore, Kaushik et al (1988) found that urea pathway accounted for less than 50% of arginine catabolism in rainbow trout. Different patterns of plasma urea production might result from the differences of fish food habits, living habits, or the ability to response to both dietary and environmental changes (Chiu et al, 1986;Twibell and Brown, 1997). Anyhow, plasma urea in response to dietary arginine, is less clear and further studies are needed to investigate not only the effects of dietary amino acid levels and/or balance but also the contribution of organs or tissues other than liver to urea production.…”