Effects of post-irradiation interval on translocation frequency in male mice.

Hybrid male mice were given 5 Gy + 5 Gy acute X-rays 24 h apart, with cytological examination of testes 16-19, 39-42 and 64-66 weeks later. Mean testis weights were significantly lower in the youngest group than in the other two. However, translocation frequencies in spermatocytes of the youngest group (mean of 0.57 per cell) were significantly higher than in either of the other two groups, which gave similar values averaging 0.36 translocations per cell. There was highly significant heterogeneity in translocation yields within the youngest group. The decline in translocation yield with time after irradiation is in line with that reported by Léonard and Deknudt (1970) in inbred strain C57BL males. Analysis of all available data suggests that high translocation yields are found during late stages in the process of germ-cell repopulation of the testis after high radiation doses and may be connected with changing frequencies of radiosensitive and radioresistant stem cell populations as repopulation proceeds.