Effects of X-irradiation on mouse blastocysts

Early morphological changes in the trophectoderm and inner cell mass of mouse blastocysts, which were exposed to X-irradiation at a dose of 2 Gy, were light- and electron-microscopically examined. After fertilization, pregnant mice were exposed to X-rays of 2 Gy at a dose rate of 0.1 Gy/min. Two, 4, 6, and 9 hours after irradiation, the mice were killed to collect blastocysts. In addition, blastocyts were collected 4 hours after 0.5, 1, 2, or 4 Gy of X-rays to examine dose-response relationships. Cytoplasmic degeneration occurred in both the trophectoderm and inner cell mass 2 hours after irradiation. Electron microscopic examination showed it to be associated with ribosome aggregation. The frequency of cells with cytoplasmic degeneration reached the peak 4 hours after irradiation and was higher in the inner cell mass than the trophectoderm. A dose-response relationship for the frequency of cells with cytoplasmic degeneration was observed in the dose range from 0.5 Gy to 4 Gy. The frequency of those cells was also higher in the inner cell mass than in the trophectoderm, regardless of radiation doses. (N.K.)