Effect of salinity acclimation on osmoregulation, oxidative stress, and metabolic enzymes in the invasive Xenopus laevis

Aquatic animals often display physiological adjustments to improve their biological performance and hydrosaline balance in saline environments. In addition to energetic costs associated with osmoregulation, oxidative stress, and the activation of the antioxidant system are common cellular responses to salt stress in many species, but the knowledge of osmoregulation‐linked oxidative homeostasis in amphibians is scarce. Here we studied the biochemical responses and oxidative responses of Xenopus laevis females exposed for 40 days to two contrasting salinities: hypo‐osmotic (150 mOsm·kg−1·H2O NaCl, HYPO group) and hyper‐osmotic environments (340 mOsm·kg−1·H2O NaCl, HYPER group). We found an increase of plasma osmolality and plasma urea concentration in the animals incubated in the HYPER treatment. Increases in electrolyte concentration were paralleled with an increase of both citrate synthase and cytochrome c oxidase activities in liver and heart. Interestingly, HYPO group had higher catabolic activity of the skin and liver total antioxidant capacity (TAC), compared with animals from the HYPER group. Moreover, there was an inverse relationship between liver TAC and plasma osmolality; and with the metabolic enzymes from liver. These findings suggest that salinity induces changes in urea metabolism and specific activity of metabolic enzymes, which appears to be tissue‐dependent in X. laevis. Contrary to our expectations, we also found a moderate change in the oxidative status as revealed by the increase in TAC activity in the animals acclimated to low salinity medium, but constancy in the lipid peroxidation of membranes. Xenopus laevis is able to trigger molecular mechanisms to tolerate different saline environments, which involve alteration of plasma urea concentration, modulation of metabolic enzymes in liver and moderate changes in the oxidative status. In general hyperosmotic environment leads to higher metabolic enzymes, but decreases the total antioxidant capacity of tissues. Research highlights We preformed an experimental assesment of ionic stress on a frog species. Frog exposed to saline water for 40 days displayed higher urea concentration and metabolic enzymes of internal organs. Salinity induces changes in antioxidant capacity but without sign of oxidative stress.