The relative biological effectiveness of low doses of 14 MeV neutrons in steady-state murine spermatogenesis as determined by flow cytometry

The relative biological effectiveness of 14 MeV neutrons in the low-dose ra nge II Gy has been determined in differentiating and differentiated spermat ogonia. Male NMRI mice were exposed to single doses of 2 cGy to 3 Gy of Co- 60 gamma rays or neutrons. The ratios of testicular S-phase cells, 4c prima ry spermatocytes, and elongated spermatids were quantified by DNA how cytom etry 2 to 70 days after irradiation and were found to decrease. Histologica l samples and testis weight were analyzed in parallel. Doses of 2-5 cGy neu trons and 10-50 cCy gamma rays significantly (P < 0.05) decreased the propo rtions of S-phase cells, spermatocytes and elongated spermatids at 4, 14 an d 28 days postirradiation. For S-phase cells, the biphasic shape of the cel l survival curves was described with a D-50 of 5 cCy neutrons. The D-50 for Co-60 gamma rays and the relative biological effectiveness could not be de termined. The relative biological effectiveness of neutrons at 50% reductio ns of testis weight, primary spermatocytes, and elongated spermatids were 2 .5, 10.0 and 6.1, respectively. This in vivo assay Is interesting because o f its sensitivity at dose ranges that are relevant for exposures in the env ironment, the workplace and radiotherapy, (C) 2000 by Radiation Research So ciety.