The effects of chronic whole-body irradiation on the reproduction of C-57 black mice

One thousand C -57 black mice were exposed to chronic continuous radiation from a Co⁶⁰ source. The dose rates employed were 0, 2, 5, 10 and 20r per day (23 hours), for total accumulated doses of 0, 60, 120, 240, 480 and 600r. Forty-eight mice were employed in each of the rate groups and each of the total dose groups. The effects on reproduction and resulting degenerative changes in the gonads were evaluated for each total dose, which was received at each of the various rates. The reproductive capability of thirty-two of the forty-eight mice were evaluated by the following matings in each group: six control females and two control males; six control females and two irradiated males; six irradiated females and two control males; and six irradiated fem a le s and two irradiated males. Concurrent with the above matings sixteen mice (four irradiated, four controls, four males and four females) were sacrificed for histological examination. The criteria set for evaluating the histological results for the males were: number of stage IX tubular cross sections per 500 tubules counted; diameter of seminiferous tubules; weight of testes; average number of type A spermatogonia, spermatocytes in leptotene and pachytene stages of development, developing spermatozoa, and sertoli cells per stage IX tubular cross section . For evaluating the reproductive capability of the males the criterium was a litter produced within three weeks after removal from the radiation field. These observations led to the following general conclusions: (1) C - 57 black males are more radiosensitive than females when exposed to chronic ionizing radiation; (2) there is a definite age effect which expresses itself for each total dose, but which is dose -rate dependent; (3) results in general show a decrease in sterilizing effect with a decrease in dose -rate even though at certain stages an inverse relation can be demonstrated.