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Enhancement of Adaptive Resistance against a Variety of Chronic Stress Conditions by Plant Adaptogens: Protective Effects on Survival and Embryonic Development of Lymnaea stagnalis

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The main aim of the studies presented in this paper was to evaluate whether standardized extracts from the plant adaptogens Eleutherococcus senticosus (SHE-3) and Rhodiola rosea (SHR-5) were able to enhance adaptive resistance during chronic stress. Adaptive resistance was studied in terms of survival of developing larvae of the pond snail Lymnaea stagnalis. Larvae were exposed, for a period of up to 7 days, to either one of the following stress conditions: an enhanced temperature (33°C), the metals copper (10 μM) and cadmium (2.5 μM), as well as the oxidative stress inducers: menadione (7.5 μM) and arsenite (300 μM). During the period of chronic exposure to these stressors, different concentrations of Eleutherococcus or Rhodiola were added, in order to evaluate their abilities to enhance adaptive resistance. Rhodiola exerted a significant protective action against all chronic stress conditions and showed an ability to prevent or postpone the so-called 'stress exhaustion' phase. The effect of Eleutherococcus appeared to be more variable. A very significant protective action was observed when embryos were chronically exposed to copper. However, Eleutherococcus was only able to show a small but significant postponement of the exhaustion phase when developing larvae were chronically exposed to enhanced temperature. A high concentration of Eleutherococcus, which exerted a very significant protection against copper, caused an enhanced sensitivity of developing embryos when exposed to cadmium. Lower concentrations of this adaptogen, however, showed small, but significant protective effects against chronic cadmium exposure. Adverse effects of Eleutherococcus (1 mg/ml) were observed in the combination with chronic exposure to menadione or arsenite, which were known to induce oxidative stress. It is concluded that plant adaptogens did not always show protection in chronically stressed embryos of Lymnaea stagnalis. Although the precise mechanism by which adaptogens exert their effect remains elusive, it is suggested that the effects of Rhodiola and of Eleutherococcus are based on different mechanisms of action. Based on these results, it is suggested that Rhodiola can be characterized as a general enhancer of adaptive resistance during chronic environmental stress, whereas Eleutherococcus only shows clear protective effects in case of copper exposure and therefore appears to be more limited or specific in its ability to initiate adaptive resistance. The observations presented in this paper require a further refinement of the definition of adaptogens.

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