Fundamental study for development of a new preventive method of radiation pneumonitis

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The purpose of this study was to reveal the anti-fibrotic effect of spironolactone after pulmonary irradiation by an experimental system of rats. Female Wistar rats underwent local irradiation of the right whole thorax with a single dose of 15Gy by 200kVp x-rays. 90-day release pellets of 200mg of spironolactone were implanted in the rat's left back subcutaneously before or after irradiation. 13 weeks after irradiation, rats were sacrificed and bilateral lungs were removed and fixed in buffered formaldehyde for histopathological examinations. Fibrotic changes and foamy macrophage infiltrations were evaluated for each lung. The fibrotic changes of the irradiated lungs were severer when spironolactone was administered before irradiation. If spironolactone administration was delayed after irradiation, fibrotic change was not suppressed by spironolactone. Foamy macrophage infiltrations were not significantly different among the groups of different timings of spironolactone administration.