Histological examination of the effect of differently fractionated irradiations in rat and mouse organs. III. Autoradiographic examination of DNA synthesizing cells in locally X-irradiated rat spleens.

The spleen of rats was irradiated with 50 Gy dose local X-rays in two different fractionation rhythms, i.e. twice a week given high and daily applied lower fractions of radiation. According to the results of 3H-thymidine autoradiography made after the last irradiation 24 hours later both in the white and the red pulp the labelling index was less on the effect of twice in a week applied high radiation fractions than in case of daily given lower fractions. This indicate in correlation with the results of earlier analogous histological experiments that the damaging effect of rarely given higher fractions of radiation in the spleen is especially obvious.