Purpose: Primary conditioning low dose irradiation suppresses the molecular
responses against secondary challenge high dose irradiation; this phenomen
on has been termed the radioadaptive response. The mechanism of the radioad
aptive response is not yet clear. This study was undertaken to elucidate th
e radiation response of apoptosis in mouse spleen after whole-body irradiat
Materials and methods: The induction of apoptosis was analysed ill the sple
ens of C57BL/6N mice after chronic irradiation with gamma -rays at 1.5 Gy (
0.001 Gy/min for 25 h) followed by challenge irradiation with X-rays at 3.0
Gy (1 Gy/min).
Results: Accumulation of p53 and Bax, and the induction of apoptosis were o
bserved dose-dependently in mouse spleen 12 h after acute irradiation at a
high dose-rate. However, it was found that there was significant suppressio
n of dic accumulation of p53 and Bax, and induction of apoptosis 12 h after
challenge irradiation at 3.0 Gy at a high dose-rate following chronic prei
rradiation at 1.5 GN at a low dose-rate. In addition. the combination of pr
e-irradiation at 1.5 Gy at a high dose-rate and challenge irradiation at 3.
0 Gy at a high dose-rate could not suppress the accumulation of p53 and Bax
or the induction of apoptosis.
Conclusions: Chronic pre-irradiation at a low dose-rate suppressed Bax-medi
ated apoptosis. These findings suggest that the radioadaptive response in m
ouse spleen may be due to a suppression of p53-mediated apoptosis.