Radiation response of apoptosis in C57BL/6N mouse spleen after whole-body irradiation

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 ion. 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.