Biological impacts on the lungs in rats internally exposed to radioactive MnO particle.

To understand the radiation effects 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. Mn, 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 effects of internal exposure to MnO particle in the lung of male Wistar rats comparing to the effects of external Co-γ irradiation. Absorbed doses of internal irradiation of lungs were between 25 and 65 mGy in MnO-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 MnO particle exposure. However, mRNA and protein expressions of aquaporin 5 increased significantly in the lung tissue on day 3 postexposure in MnO groups (by 1.6 and 2.9 times, respectively, in the highest dose group). Smad7 mRNA expression was also significantly elevated by 30% in the highest dose group of MnO. Our data demonstrated that internal exposure to MnO induced significant biological responses including gene expression changes in the lungs, while external Co-γ irradiation of 2 Gy did not show any changes.