Effects on foetal ovaries after protracted, external gamma irradiation as compared with those from internal depositions.

Effects of low doses of protracted gamma irradiation on pre- and neonatally exposed ovaries in CBA mice have been compared with those previously obtained by 90Sr contamination of the dam. The total number of germ cells at 56 days of age was reduced to about 50 per cent after a dose of 0.09 Gy given during four days from the 19th day post coitum to the 2nd day post partum. The highest dose level used (0.91 Gy) reduced the frequency to about 10 per cent. Females exposed to the same dose levels at an age of 85 to 90 days showed a lesser degree of injury. The reproductive capacity in females exposed around their birth (expressed as the number of litters per female) was negatively correlated to the dose of gamma irradiation. The effects on the foetal ovaries of 2 to 5 kBq 90Sr given to the dam on the 19th day of gestation seemed to correspond to those from 0.01 Gy from 137Cs under the present circumstances.