The aim of this work was to evaluate the reproductive toxicological effects of uranium (U) at 2.5, 5, and 10 mgU/kg/d chronically administered in drinking water for 40 d. Swiss female control mice (n = 28) and mice chronically contaminated with uranyl nitrate in drinking water (n = 36) were tested. The number and quality of ovulated oocytes, chromatin organization, and nuclear integrity were evaluated. No significant differences were obtained in the numbers of ovulated oocytes between the different groups. Nevertheless, in 1,520 of the oocytes examined, dysmorphism increased from 11.99% in the control group to 27.99%, 27.19%, and 27.43% in each of the contaminated groups, respectively, in a dose-independent manner. On the other hand, morphological chromatin organization from 880 oocytes examined showed an increase in metaphase plate abnormalities from 37.20% (±7.21) in the control group to 55.13% (±21.36), 58.29% (±21.72), and 64.10% (±12.62) in each of the contaminated groups, respectively. Cumulus cell (CC) micronucleation, a parameter of nuclear integrity, increased from 0.21% (±0.31) in the control group to 1.92 (±0.95), 2.98 (±0.97), and 3.2 (±0.98), respectively. Both metaphase plate abnormalities and CC micronucleation showed an increase in a dose-dependent manner (r = 0.9; p < 0.001). The oocyte and its microenvironment showed high sensitivity to uranium contamination by drinking water. The lowest observed adverse effect level for this system is estimated at a level below 2.5 mgU/kg/d for female mice.
* CNEA, Vuelta de Obligado 2893, Ciudad Autonoma de Buenos Aires, 1429 Argentina.
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(Manuscript accepted 3 December 2008)