en Radiation Biology Radiation Biology تحقيق بديع Original Research Background: The present study has been carried out to investigate the effects of preovulatory stage gamma-irradiation of female mice in the absence or presence of vitamin E on numerical chromosome abnormalities in 8-cell embryos after mating with non-irradiated males. Materials and Methods: The 8-11 weeks adult female NMRI mice were whole body irradiated at preovulatory stage (post PMSG injection and about 12-18 hours before injecting HCG) with 4 Gy gamma-rays generated from a cobalt-60 source alone or in combination with 200 IU/kg vitamin E, intrapretoneally administered one hour prior to irradiation. Soon after HCG injection super ovulated irradiated females were mated with non-irradiated males. About 68-h post coitous (p.c), 8-cell embryos were flushed from the oviducts of pregnant mice and were fixed on slides using standard methods in order to screen for metaphase spreads and numerical chromosome abnormalities. Results: In control embryos, 8% of metaphase plates were aneuploid, whereas in preovulatory stage irradiated female mice, about 50% of metaphase plates of embryos showed numerical chromosome aberrations ( P<0.001 ). Administration of vitamin E one hour before the irradiation reduced chromosomal aberrations significantly (P=0.005). Conclusion: Results show that the effects of gamma-irradiation on preovulatory stage oocytes led to chromosomal abnormalities in subsequent embryos generated by these oocytes. Increase the frequency of numerical chromosome abnormalities -mostly aneuploidy- may be due to abnormal chromosomal non disjunctions during 2nd meiotic division. Reduction of the frequency of chromosome aberrations in the presence of vitamin E is probably due to antioxidant effects of this vitamin, and scavenging free radicals induced by gamma-rays in mice oocytes’ environment. Preimplantation embryos, chromosomal abnormalities, mouse oocytes, gamma-rays, vitamin E 35 40 http://ijrr.com/browse.php?a_code=A-10-1-187&slc_lang=en&sid=1 M. Salimi 79003194753284600540 79003194753284600540 No H. Mozdarani mozdarah@modares.ac.ir 79003194753284600541 79003194753284600541 Yes