methysergide SOD CAT and GST activities were lower in P ridibundus

SOD, CAT and GST activities were lower in P. ridibundus. At the same time, the concentration of GSH in the liver of P. ridibundus was higher. GSH is an important radical scavenger if the reaction with SOD is prevented (Munday and Winterbourn, 1989). Lower SOD, CAT and GR activities was accompanied by higher GSH-Px activity in P. ridibundus, suggesting that coordinated action toward hydrogen peroxide induced oxidative attack.
Results of our investigation revealed similar antioxidative response in P. lessonae compared to P. ridibundus. The higher activity of liver SOD which generates H2O2 is counter balanced by lower CAT and GR activities. The produced H2O2 can be detoxified by CAT and GSH-Px. In P. lessonae, H2O2 is eliminated by higher GSH-Px activity, thus compensating for lower CAT activity.
In the liver of P. kl. esculentus we observed opposite trends in CAT and GSH-Px activities. Liver CAT activity was higher while the activity of GSH-Px was lower. Similar trends in GR and GST activities were observed. Higher GR activity can be linked with a lower GSH concentration in the liver of P. kl. esculentus and with attempts of the liver to maintain physiological GSH concentration. GR has a crucial role in preserving normal functioning of GSH-dependent methysergide (Deponte, 2013).
GST and AChE activities can be used as biomarkers of pollution with xenobiotics, especially organophosphorus and carbamate pesticides (Hayes and McLellan, 1999; Hobbiger, 1961). Booth et al. (1998) reported that two organophosphorus pesticides, chlorpyrifos and diazinon, affect GST and AChE activities in earthworm Apporectodea caliginosa. The pesticides induced opposite trends, with GST increasing and AChE decreasing (Booth et al., 1998). A similar trend was reported by Gungordu (2013) who studied different frog species exposed to pesticides. In our study, GST activity was significantly higher in the liver of P. kl. esculentus than in parental species. Lower AChE activity was reported in the liver of P. ridibundus and P. kl. esculentus when compared to P. lessonae. The results of examinations of GST and AChE activities suggest that P. kl. esculentus react to the presence of some organic xenobiotics. Fagotti et al. (2005) reported that the degree of organochlorine pesticide bioaccumulation was higher in the hybrid P. kl. esculentus than in the host species P. lessonae.
Non-denaturing electrophoresis detected CAT and SOD isoforms. Results of CAT activity revealed the presence of one isoform in all species. The band was more intense in P. kl. esculentus compared to parental species. These results are in agreement with the activities of CAT that were assessed spectrophotometrically. De Quiroga et al. (1985) also reported the presence of one CAT isoform in the liver of R. ridibunda. SOD isoforms S1 and S3 detected in all three species exhibited similar patterns, whereas isoform S2 displayed considerable variation.
Canonical discriminant analysis revealed that liver CAT, GR, GST and GSH-Px activities significantly contributed to differentiation between hybrid P. kl. esculentus and parental species P. ridibundus and P. lessonae. CAT, GR and GST activities were significantly higher in P. kl. esculentus, while GSH-Px was significantly lower when compared to the parental species. The main contributors to differentiation between parental species were SOD and AChE activities. SOD and AChE activities were significantly higher in P. lessonae.

Conclusion
The parental species, P. ridibundus and P. lessonae, display more similar antioxidative responses to environmental-induced oxidative stress than the hybrid P. kl. esculentus. Our results suggest that the preferred pathway of H2O2 detoxification in P. kl. esculentus utilizes CAT and GSH-Px in P. ridibundus and P. lessonae. The antioxidative strategy of P. kl. esculentus, suggests that the hybrid could be better equipped for fighting against environmental-induced oxidative stress, and the one of the reasons was it has broader environmental tolerance as compared to the parental type. The overall results supports hypothesis of heterozygote superiority. The obtained results point the way for comparative physiological studies of wildlife species. These findings are a potentially useful tool for understanding the physiology and long-term conservation of the P. esculentus complex frogs.