Biological Effects of Continuous Low-Dose-Rate Irradiation in Silkworms and Mice : Growth Promotion and Tumor Transplantability

概要

[Purpose]
A previous study showed that continuous low-dose-rate irradiation promoted the growth
of silkworm larvae. This study aimed to confirm that finding, determine the optimal
dose rate for growth promotion, and compare low- and high-dose-rate irradiation in
silkworms, while also investigating the effects of the radiation-emitting sheet on growth
and tumor transplantability in mice.
[Materials & Methods]
Silkworm eggs were placed on low-dose-emitting sheets with 4 different dose rates (gray rate: 1.7 -22.4 mSv/hour) or on control sheets. The other groups of silkworm larvae
received single whole-body X-irradiation (0.1-50 Gy), and subsequent body weight
changes were monitored. Starting at 3 weeks old, Balb/c mice were bred on the same
sheets, and body weight change was measured. Seven weeks later, the mice were used
to investigate the transplantability of EMT6 tumor cells cultured in vitro.
[Results]
The silkworms bred on the 13.4- and 22.4-mSv/hour sheets became larger than the
control. Single 50-Gy irradiation suppressed the growth of silkworms. An increase in
the time to EMT6 tumor development was observed in low-dose-rate-irradiated mice.
[Conclusion]
This study confirmed growth promotion of silkworms by continuous low-dose radiation
and demonstrated growth suppression at a high dose rate. Growth promotion was not
observed in mice; further studies using higher dose-rate sheets may be warranted. ...