Abstrakt: | The aim of this study is to determine whether there are typical interactions and
relationships among activities of indicative enzymes of free-radical scavenger
system under the influence of environmental stressors. Animals representing various
taxonomic groups: laboratory mice, rats, frogs, slugs of genus Agrolimax and Arion,
earthworms Dendrobaena and Lumbricus, as well as Madagascar cockroach
Gromphadorhina were treated with agents known for their prooxidative or
antioxidative activity, such as: cadmium, paraquat, carbon tetrachloride, selenite
and vitamin E. Diversified time schedules and ways of treatment with these agents
were used in order to produce alterations of enzymatic activities and to assess
whether there are essential relationships and signs of compensation among indices
of antioxidative processes. The activity of superoxide dismutase, glutathione
peroxidases, glutathione reductase, glutathione S-transferase, catalase as well as
iron-ascorbate-stimulated lipid peroxidation and the content of thiobarbituric acid
reactive substances were measured.
When various doses of paraquat and cadmium were applied to mice, frog or
invertebrate species the examined enzymes responded in a biphasic manner,
characterised by an increase after lower and a decrease after higher doses. In some
cases inverted biphasic pattern was also observed. The complex, “mosaic”
alterations of enzyme activity within various organs, characterised by opposite
changes of examined parameters were observed and explained as resulting from
a diverse distribution of applied compounds within organism as well as from specific
susceptibility of particular organs and enzymes. Additionally, the “mosaic” response
pattern may reflect another aspect of biphasic dose-response relationships in the
examined organs.
Since a compensation of altered activity of peroxidase related pathway of free
radical scavenger system by opposite alteration of superoxide dismutase and catalase
activity was observed in several cases, the hypothesis on the mutual compensatory
relations within antioxidative system was drawn and summarised as follows. An
inhibition of Se-dependent glutathione peroxidase related pathway of free radical
scavenger system in the organs of prooxidant-treated animals may provoke
a stimulation of catalase and superoxide dismutase activity, which compensates for this inhibition. This mechanism possibly acts also in the opposite direction,
compensating decreased activity of catalase with glutathione peroxidase or
glutathione S-transferase activity. Additionally, some evidence was obtained for
the compensation of decreased glutathione peroxidases activity by increasing
reaction rate of these enzymes due to enhanced flux and availability of reduced
glutathione, on condition that activity of glutathione reductase will rise sufficiently
and the pool of reduced nicotinamide dinucleotide phosphate (NADPH) is
maintained.
The general frame of mutual compensatory mechanism within the antioxidative
system postulated here seems to be common and universal, at least in the examined
vertebrate species, insects and earthworms.
Other observations and conclusions were also drawn on the basis of presented
results. |