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BEHAVIOUR OF THE OXIDANT SCAVENGER METALLOTHIONEIN IN HYPOXIA-INDUCED NEOTROPICAL FISH
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Abstract
The pacu (Piaractus mesopotamicus) is a hypoxia-tolerant neotropical fish species. There is little or no
information in this species regarding biochemical adaptations to waters with different oxygen
concentrations, such as the production of reactive oxygen species and antioxidant scavengers, which
might be of interest in the study of antioxidant defense mechanisms. Metallothioneins (MT) have been
widely applied as biomarkers for metal exposure in fish liver, and, recently, in bile. These metalloproteins,
however, have also been reported as free radical scavengers, although studies in this regard are
scarce in fish. In this context, normoxic and hypoxic controlled experiments were conducted with pacu
specimens and MT levels were quantified in both liver and bile. Reduced glutathione (GSH) indicative of
oxidative stress, and thiobarbituric acid reactive substances (TBARS), indicative of lipid peroxidation,
were also determined in liver. The results demonstrate that hypoxic fish present significantly lower
metallothionein levels in liver and bile and lower reduced glutathione levels in liver, whereas lipid
peroxidation was not significantly different between hypoxic and normoxic fish. The results of the
present study seem to suggest that metallothioneins may actively participate in redox regulation in
hypoxic fish in both bile and liver. MT levels in these organs may be temporarily suppressed, supporting
the notion that down-regulation of oxidant scavengers during the oxidative burst is important in defense
signaling in these adapted organisms.
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