Effects of dose and dose-rate of gamma radiation on follicular development and reproduction capacity of the rat

The objectives of this study were to determine both the effects of y-radiation on the oocyte of the rat and the relationship between numbers of viable oocytes at various times postirradiation and long term reproductive performance. Two hundred animals, initial age 50 days, were used in this study. Using 40 control animals, the remaining 160 animals were divided equally into four groups and irradiated with ⁶⁰Co gamma radiation at the following doses and rates: 200 R at 1 R per minute, 200 R at 50 R per minute, 400 R at 1 R per minute, and 400 R at 50 R per minute. Following irradiation, all animals were subjected to continuous breeding until 150 days postirradiation, at which time the experiment was terminated. At 10, 70, 90, and 110 days postirradiation, 50 animals (10 per treatment group) were unilaterally ovariectomized for histological evaluation of the ovarian population at each postirradiation interval. At the termination of the experiment, the remaining ovary was taken for histological evaluation of the residual population following breeding and irradiation. The primordial follicle population was drastically reduced by all irradiation levels at 10 days postirradiation. There was also a difference in response to dose and dose rate. The numbers were further reduced by age at 70 days postirradiation. There was, however, no further decline in the primordial follicle population at the 90 and 110 day intervals. The growing follicle numbers were reduced at 10 days postirradiation by 200 R at 1 R per minute, 400 R at 1 R per minute and 400 R at 50 R per minute, but not by 200 R at 50 R minute. At 70, 90, and 110 days postirradiation, the growing follicle populations were further depleted by all irradiation treatments. At 10 days postirradiation, the vesicular follicle numbers were not affected by any of the irradiation levels. However, by 70 days post irradiation, the population was reduced by all treatments and age. The relationship of follicle numbers surviving irradiation and reproductive performance was tested and a relationship was demonstrated between the number of primordial follicles surviving irradiation and subsequent progeny produced after 70 days postirradiation by both 400 R dose rates (P < 0.05). A relationship also existed between growing follicles and progeny production in the 200 R at 50 R per minute and 400 R at 1 R per minute groups at 70 days postirradiation (P < 0.05). A relationship was not elucidated between the vesicular follicles and subsequent progeny produced. Based on the results obtained in this study, there does not appear to be a significant relationship between numbers of germ cells and progeny production in nonirradiated female rats. However, the irradiation treatments which were imposed did significantly reduce the number of germ cells and subsequent pup production.