Abstract:
To understand the radiation efects of the atomic bombing of Hiroshima and Nagasaki among the
survivors, radiation from neutron-induced radioisotopes in soil should be considered in addition to
the initial radiation directly received from the bombs. 56Mn, which emits both β particles and γ-rays,
is one of the dominant radioisotopes created in soil by neutrons from the bomb. Thus we investigated
the biological efects of internal exposure to 56MnO2 particle in the lung of male Wistar rats comparing
to the efects of external 60Co-γ irradiation. Absorbed doses of internal irradiation of lungs were
between 25 and 65 mGy in 56MnO2-exposed animals, while the whole body doses were between 41
and 100 mGy. Animals were examined on days 3 and 61 after the exposure. There were no remarkable
pathological changes related to 56MnO2 particle exposure. However, mRNA and protein expressions of
aquaporin 5 increased signifcantly in the lung tissue on day 3 postexposure in 56MnO2 groups (by 1.6
and 2.9 times, respectively, in the highest dose group). Smad7 mRNA expression was also signifcantly
elevated by 30% in the highest dose group of 56MnO2. Our data demonstrated that internal exposure
to 56MnO2 induced signifcant biological responses including gene expression changes in the lungs,
while external 60Co-γ irradiation of 2 Gy did not show any changes.
