The induction of reciprocal translocations in mouse germ cells by chemicals and ionizing radiations. I. Dose-response relationships and combined effects of bleomycin with thio-tepa and gamma-rays

The effect of bleomycin (BLM) on mouse stem cells has been analysed using the spermatocyte test. The dose-response relationships after treatment with doses of 20, 40 and 60 mg/kg of the compound as well as the combined effect of BLM and gamma-rays and BLM and thio-tepa (TT) were studied. A positive, significant correlation between the dose of BLM and the frequency of translocations was found. Two different responses were found when the yields of translocations induced after combined treatments, separated by a lapse of 24 h, were compared with the sum of translocation frequencies induced after the corresponding single treatments: (1) Potentiation, in the treatments with 1 Gy plus 9 Gy and 60 mg/kg of BLM plus 9 Gy; (2) additivity, in the treatments with 60 mg/kg of BLM plus 1 Gy, 1 Gy plus 60 mg/kg of BLM, and 0.2 mg of TT plus 60 mg/kg of BLM. In mice irradiated with 1 Gy plus 9 Gy and mice treated with 60 mg/kg of BLM plus 9 Gy, similar translocation yields were found. The potentiating effect of BLM is similar to that obtained with non-radiomimetic compounds such as triethylenemelamine, cyclophosphamide and adriamycin. These results are discussed taking into account the hypothesis of germ cell selection, and the dose of radiation employed.