Combined effects of radiation and ultrasound on ICR mice in the preimplantation stage

Abstract

Embryos of ICR mice at the preimplantation stage of development were used to examine the single and combined effects of ultrasound (US) and radiation. Pregnant mice were exposed to a single dose of whole body gamma radiation and/or US at 2 hpc (hours postconception) or 3 hpc. The exposure duration was 10 min with 1-MHz continuous wave US at 1 or 2 W/cm2 by ISPTA (intensities of spatial peak temporal average). Gamma irradiation of pregnant mice (2 hpc) was at 0.5 Gy at a dosage rate of 0.2 Gy/min. The rate for ultrasonic irradiation was a dose of 1 or 2 W/cm2, considered by some to be too high in therapy, such as for arthritis in the rehabilitation area of the medical application. Various malformations were recognized, and the incidence of malformations in the 0.5-Gy exposure and the control groups were compared. A greater number of malformations were observed in the 0.5-Gy exposure group relative to the 0.5-Gy plus 1.0 W/cm2 US exposure group. Therefore, the synergistic effects of radiation relate to external malformations, the number of implantations, and the rate of embryonic death due to US. It appears that US may act to repair DNA damaged by ionizing radiation. The cell cycle of the fertilized egg is delayed, which may be the mechanism by which lesions induced by ionizing radiation are healed by ultrasonic irradiation. (E-mail:gu@suzuka-u.ac.jp)