The effects of radiation dose-rate and quality on the induction of dominant lethals in mouse spermatids.

Hybrid male mice were given 3 Gy (300 rad) doses of X- or gamma-irradiation at dose-rates of either 0.6 or 0.002 Gy/min for each radiation. Germ-cells treated as spermatids were tested for dominant lethality. Effects on spermatogonia were evaluated by studying testis-weight, sperm-count and sperm abnormalities. The rate of induction of dominant lethal mutations was 2.1 times as high after acute X-irradiation as after protracted gamma-irradiation. Most of this difference resulted from the change in radiation quality, since the relative effectiveness of X- versus gamma-irradiation was 1.9 at low and 1.6 at high dose rates. For each radiation, however, fewer dominant lethals were induced at low dose-rates than at high (low/high ratios of 0.8 and 0.9 respectively) although differences did not reach a significant level. There were no statistically significant effects of dose rate on testis-weight or sperm-count in the X-ray series, but there were significantly less severe effects on both with protraction of the gamma-irradiation. Evidence for effects of radiation quality on these characters was conflicting. Frequencies of abnormal spermatozoa were markedly increased 7 weeks after irradiation but there were no consistent effects of radiation intensity or quality.