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artículo con referato
"Metabolic Alterations Without Metal Accumulation in the Ovary of Adult Bufo Arenarum Females, Observed After Long-Term Exposure to Zn2+, Followed by Toxicity to Embryos"
F. Naab, M. Volcomirsky, A. Burlón, M.E. Caraballo, M. Debray, J.M. Kesque, A.J. Kreiner, M.J. Ozafrán, J.A. Schuff, P. Stoliar, M.E. Vázquez, J. Davidson, M. Davidson and T. Fonovich de Schroeder
Arch. Environ. Con. Tox. 41(2) (2001) 201-207
Long-term exposure of aquatic organisms to metals, even those considered as micronutrients, may affect their metabolism and produce them sub lethal effects. We evaluated the effects of chronic exposure of adult amphibian (Bufo arenarum) females to 4 µg/L of Zn2+ (ZnSO4·H2O) in Ringer solution, on the concentration of Zn and Fe, the activity of the key enzyme of the pentose phosphate pathway: glucose-6-phosphate dehydrogenase and glutathione content, both in the liver and ovary of these animals. We also performed early embryonic development studies by in vitro insemination from both control and treated females. Zn exposure rendered lower Zn concentrations in the ovaries than did exposure of animals to Ringer solution without metal addition (96.9 ± 49.7 vs 149.23 ± 46.4 Zn µg/wet tissue g). Zn and Fe concentrations correlation was positive and linear in the ovary while it was negative and non linear in the liver of the studied females. The activity of the enzyme glucose6-phosphate dehydrogenase decreased (0.0599 ± 0.0109 vs 0.0776 ± 0.0263 µmol of NADPH/min.mg of proteins) and the endogenous glutathione content increased (0.02679 ± 0.00488 vs 0.01767 ± 0.0074 mg/10 mg of proteins) in the ovary but remained unaltered in the liver as a consequence of Zn treatment. Our results suggest the existence of different mechanisms of regulation of Zn and Fe concentrations in the ovary and in the liver of adult Bufo arenarum females. Binding of Zn to low molecular weight proteins, as metalothioneins, may occur in the liver, thus protecting this organ from toxic effects. In the ovary Zn should be able to bind high molecular weight proteins, like glucose-6-phosphate dehydrogenase, and produce oxidative stress leading to the observed increased in endogenous glutathione content. Inhibition of the pentose phosphate pathway in the ovary by Zn can be responsible of the reproductive failure that we detected through embryos survival studies during early life stages (81.3 ± 6.3 % of survive from control females vs 63.1 ± 13.8 % of survive embryos from Zn treated females at the branchial circulation stage of development).
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