CONICET | Buscador de Institutos y Recursos Humanos

Amphibian embryos are naturally exposed to prooxidant conditions throughout their development. Environmental exposure to contaminants may affect their capacity to respond to challenging conditions, to progress in a normal ontogenesis, and finally to survive and success in completing metamorphosis. We studied the effects of the exposure to two anticholinesterase agents, the carbamate carbaryl and the organophosphate azinphos methyl, on the antioxidant defenses of the toad Rhinella (Bufo) arenarum developing embryos. Reduced glutathione (GSH) levels were early increased by carbaryl, but decreased by both pesticides at the end of embryonic development. The GSH-dependent enzymes glutathione reductase and glutathione peroxidases showed oscillating patterns that could be attributed to an induction of activity in response to oxidative stress and inactivation by excess of reactive oxygen species. Glutathione-S-transferases, which may participate in the conjugation of lipid peroxide products in addition to pesticide detoxification, showed an increase of activity at the beginning and at the end of development. Catalase also showed variations in the activity suggesting successively induction and inactivation in response to oxidative stress due to pesticide exposure. Superoxide dismutase activity was induced by carbaryl and transiently decreased by azinphos methyl exposure. Judging by the depletion in GSH levels and glutathione reductase inhibition at the end of embryo development, the oxidative stress caused by azinphos methyl seemed to be greater than that caused by carbaryl, which might be in turn related with a higher number of developmental alterations caused by the organophosphate. GSH content is a good biomarker of oxidative stress in the developing embryos exposed to pesticides. The antioxidant enzymes are in turn revealing the balance between the protective capacity and the oxidative damage suffered on their own molecules. Keywords: Amphibian development, oxidative stress, organophosphates, carbamates, glutathione

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