Dose-rate effect of ethylene oxide inhalation exposures on DNA breakage in mouse spermatids

Experiments were performed to determine if the amount of DNA breakage in mouse spermatids exposed to EtO is altered by different rates of exposure. To assay for DNA breakage, an alkaline elution procedure was used. For each experiment, one group of (C3H x BL10)F1 male mice had their germ-cell DNA pre-labeled with 3H-thymidine and were subsequently exposed to EtO. A second group of males had their germ-cell DAN pre-labeled with 14C-thymidine and served as controls. Nine days following EtO exposure, spermatozoa from the vasa deferentia of treated and control animals were place together on a polycarbonate filter and lysed. Any small pieces of single-stranded DNA resulting from breakage by the EtO pass rapidly through the filter, while normal-sized DNA takes considerably longer to pass through. The amounts of treated and control DNA eluted were then determined using liquid scintillation counting techniques. The mice were given inhalation exposures of EtO at three different dose rates, but the total exposure was fixed at 1800 parts per million (ppm) -h. The rates of exposure were: 1800 ppm for 1 h, 900 ppm for 2 h, and 450 ppm for 4 h. The results showed that with an exposure of 1800 ppm for 1 h the amount of DNA eluted from the sperm cells of EtO-exposed animals was 36%. With an exposure of 900 ppm for 2 h, 22% of the treated sperm DNA eluted; and with 450 ppm for 4 h, 16% of the treated sperm DNA eluted. Thus, the amount of DNA breakage in mouse spermatids after inhalation exposures to EtO is clearly affected by the rate at which the animals are exposed to the chemical