Effects of neonatal ovarian X-irradiation in the Chinese hamster. II. Absence of chromosomal and developmental damages in surviving oocytes irradiated at the pachytene and resting dictyate stages.

Ovaries of Chinese hamsters were irradiated with 1 Gy of X-rays on day 0, 4, 8 and 14 after birth, and the late effects on pachytene and resting dictyate oocytes, which had been proven to be radioresistant and to survive acute oocyte-killing, were studied in the progeny of the irradiated females. Thirty hours after mating, fertilized ova were collected and female pronuclear chromosomes were karyotyped. On day 18.5 of gestation, the number of corpora lutea and implantation sites were counted and the live and dead fetuses were examined phenotypically. There was no increase of chromosome aberrations in female pronuclei of one-cell embryos of the irradiated groups. There was no significant difference in the incidences of pre- and postimplantation deaths and of congenital malformations between the irradiated groups and the non-irradiated controls. These findings indicated clearly that oocytes at the pachytene and resting dictyate stages which had survived the acute oocyte-killing effects of X-rays were also free from late deleterious effects on genetic and developmental abilities. The radiosensitivity of oocytes of the Chinese hamster was compared with that of the mouse with respect to chromosome aberrations, lethal mutations and congenital anomalies, and the difference between both species was discussed.