Adaptive response of mouse thymic lymphoma with low dose gamma irradiation

This review describes whether there is the adaptive response in carcinogenesis of a mouse model leukemia. The response, firstly found in human lymphocytes, concerns the reducing effect of pre-irradiation on chromosome aberration rate. At the whole body level, suppression or delay of tumor development by the response is reported: In mice irradiated with 2 Gy, thymic lymphoma is observed in 46% whereas the rate is reduced to 42.5-30% in animals pre-irradiated once to 10 times with 0.1 cGy. In mice receiving the adaptive dose of 1 cGy and the transplantation of barcle 95 tumor cells derived from the above lymphoma, the tumor development in 100% of the control is reduced to 70%. The adaptive irradiation with 1 cGy is also effective in vitro to suppress neoplastic transformation of mouse fetal cells by 4.0 Gy irradiation. Repair mechanisms of DNA damage and participation of signal transduction mediated by protein kinase C are proposed at the molecular level for possibly explaining the mechanism of adaptive response, however, the problem still remains to conclude there is the response in author's carcinogenic process. (K.H.)