Studies on dose-response relationships for induction of chromosome aberrations in stem-spermatogonia of the crab-eating monkey after low and high dose-rate γ-irradiation

Radiation-induced reciprocal translocations in stem-spermatogonia were examined with the crab-eating monkey, Macaca fascicularis. Monkeys were subjected to acute gamma irradiation at the dose rate of 0.25 Gy. The frequency of the translocation was 0.09% (65/3,500 cells) in the 1 Gy group, 2.50% (74/3,000 cells) in the 2 Gy group, and 1.30% (40/3,000 cells) in the 3 Gy group. Linear dose-response relationship for translocation induction lied in the range of 0 to 1 Gy. The dose-response curve was well fitted with the linear equation indicated by Y=1.08 x 10-3 + 1.79 x 10-2 D. In the range of 0 to 3 Gy, the dose-response curve was humped with a peak yield around 2 Gy. When the monkeys received chronic gamma irradiation (1.8 x 10-5 Gy/min, approximately 0.024 Gy/22 h/day), the frequency of translocation was 0.15% (11/7,500 cells) in the 0.3 Gy group, 0.27% (16/6,000 cells) in the 1.0 Gy group, and 0.33% (13/4,000 cells) in the 1.5 Gy group. The dose-response relationship for translocation was linear with a regression coefficient of 0.16 x 10-2 and was expressed as Y=0.94 x 10-3 + 0.16 x 10-2 D. The frequency of translocation was approximately ten times higher in the group receiving high dose rate gamma iradiation than that receiving low dose rate irradiation (1.79/100 cells vs 0.16/100 cells). Dose-response relationship was noticeable in the case of crab-eating monkeys. (Namekawa, K)