Response to lethal radiation in the postnatal survival rescued by radioadaptive response from fetal radiation in mice

Studies on the radioadaptive response (AR) in rodents retrospect to 1960 for the editio princeps by Maisin et al, stating a slight increased 30-day survival rate induced by preirradiation in rats. The first report on a significantly enhanced survival rate induced by preirradiation was by Yonezawa et al in 1990 in ICR mice. Later in 2001 Ohyama et al verified this so-called "Yonezawa Effect" and demonstrated that the AR could be induced in C57BL strain mice under the similar conditions. Namely, preirradiation of 6 weeks old mice with 0.5 Gy of X-rays before a second exposure 2 weeks later to a lethal dose of 6.5 Gy significantly enhanced the survival rate from 0 to about 77% in a 30-day survival study. On the other hand, Wang et al's work in 1998 and 2000 proved the existence of AR in fetal mice in both ICR and C57BL strains. However, the postnatal survivals rescued by the AR in utero were not healthy, being significantly suffered from neurophysiological alteration and developmental retardation. In this study, the responses of the postnatal survivals to the lethal irradiation and to the AR induction were investigated in C57BL mice using 30-day survival test. A significantly increased radiosensitivity to the killing effect was observed and the AR could not be induced in the AR postnatal survivals. For those only receiving the priming dose in utero, the response to lethal irradiation and AR induction was similar to the non-irradiated animals. These findings indicated that the postnatal survivals did not response to radiation the same as the control non-irradiated animals.