Urea cycle enzymes through the development of pacu (Piaractus mesopotamicus): the role of ornithine carbamoyl transferase

Abstract

The present work reports the activities of urea cycle enzymes during the ontogenic development of the teleost pacu (Piaractus mesopotamicus). Urea cycle enzymes from the kidney and liver of adult fish were compared with those from the fish's embryonic phases. Samples were evaluated over all phases of embryonic development, the larval period and alevin. Ammonia and urea concentrations were determined during embryogenesis and in the plasma of adult fish. Except for carbamoyl phosphate synthetase-III (CPS-III), all enzymes of the urea cycle were expressed in the larvae and alevins as well as in the liver and kidney of adult fish. In spite of the low level of activity of the ornithine urea cycle (OUC) enzymes compared to those in mammals, and the low levels of tissue urea concentration compared to ammonia, the ureogenesis was evaluated in pacu. Ammonia seems to be the main nitrogenous waste during embryonic development. In this phase glutamine synthetase (GS) may play a role in ammonia detoxification, and the OUC enzymes can be individually involved in functions other than urea production. The presence of ornithine carbamoyl transferase (OCT) in all developmental phases of pacu and in the adult liver and kidney suggests that this enzyme is performing different metabolic pathways. OCT in the kidney, wherein the activity is less than in the liver, should work in the biosynthesis of polyamines and control the arginine plasma concentration given that renal arginase and argininosuccinate synthetase-argininosuccinate lyase are more active than from the liver. We suppose that OCT during the embryogenesis is a control step regulating the cellular concentration of ornithine for polyamines synthesis.

Xenobiotic‐induced changes in the arginase activity of zebrafish (Danio rerio) eleutheroembryo

“…Therefore, the estimated specific activity of 0.46 AE 0.06 IU/g wet mass is the first report for this ontogenetic stage. Nevertheless, reports have been published for freshwater fish such as Clarias gariepinus, Piaractus mesopotamicus, and marine species such as Hippoglossus hippoglossus [21,23]. Total arginase activity in the eleutheroembryo stages of these species ranged between 0.25 and 0.8 IU/g wet mass [21,22], a range that coincides with our results for D. rerio at the same developmental stage.…”

“…However, an ontogenetic variation in total arginase activity has also been observed in Clarias gariepinus, with the highest activity levels coinciding with an increase in growth factor expression associated with metamorphosis [21]. In addition, in Piaractus mesopotamicus, high levels of total arginase activity have been associated with significant increases in body mass because of tissue synthesis [23].…”

“…In the eleutheroembryo stage of fish, the enzymes involved in the urea cycle decrease their activity, which is explained by the cycle arrest. This contrasts with the progressive increase or stabilization of total arginase activity [21,22], given its relevance in cellular proliferation and differentiation [23]. Results of expression analysis by means of in situ hybridization show that in the embryonic development of D. rerio, isoenzyme type II arginase is present in tissues and organs that have differentiated (http://zfin.org).…”

Expression Pattern and Biochemical Properties of Zebrafish N-Acetylglutamate Synthase

“…This expression pattern is also consistent with the function of these enzymes in citrulline and/or arginine biosynthesis. Onset of expression of Arg1 after hatching is not unique to zebrafish and has also been observed in pacu, rainbow trout and Atlantic cod [22], [23], [29], suggesting that urea cycle enzymes may have different physiological roles at different developmental stages. Additional experiments are needed to identify precisely which cell types harbor urea cycle enzymes at different developmental stages and to draw conclusions about functions of the urea cycle in fish.…”

Metabolic and embryonic responses to terrestrial incubation of Fundulus grandis embryos across a temperature gradient

“…Alternatively, terrestrial incubation may present another strategy of ammonia elimination by volatilization. Urea is a nitrogenous end product metabolite that embryonic teleosts produce during development (Terjesen et al , ; Barimo et al , ; Monzani & Moraes, ). When the rate of ammonia production exceeds the rate of diffusion across the chorion or when embryos are in alkaline environments, conversion of ammonia into urea via the ornithine urea cycle (OUC) is a method of avoiding ammonia toxicity (Walsh, ; Wright & Land, ; Walsh et al , ).…”