X-ray sterilization of immature female rats.

Abstract

SUMMARY 1. Judged by the absence of germ cells, direct X-irradiation of ovaries of weanling rats at a level of 3150 and 4400 r leads to sterilization. Sterilization was often incomplete following exposure to 2200 r. The animals were kept under observation for 12 weeks after irradiation. Daily vaginal smears were taken after the rupture of the vaginal closure membrane. The age at which the vagina opened was about the same in animals sterilized at the age of 21–29 days as in their litter-mate controls. The rupture of the closure membrane was somewhat delayed in animals exposed to 4400 r at 18–20 days, and in unilaterally ovariectomized animals exposed to 4400 r at 23–26 days. Complete atrophy of the uterus did not occur within the experimental period of 12 weeks. The degree of involution corresponded to that of the ovaries. Changes in body weight and the weight of the pituitary and thymus were similar to those observed in adult rats following X-ray sterilization. 2. Treatment with gonadotrophins immediately after X-irradiation (at the age of 19–24 days) led to a less rapid breakdown of the vaginal closure membrane in rats exposed to 4400 r than in either similarly treated litter-mates exposed to 3150 r or their non-irradiated controls. 3. Treatment with gonadotrophins during the 5 days preceding X-irradiation (at the age of 23–26 days) was followed by an increase in subsequent secretion of oestrogen, as judged by the pattern of vaginal smears and the weight of the uterus.