A Possible Link between Diurnal Variations in Radiation Sensitivity and Cell Division in Bone Marrow of Male Mice

Abstract

Levels of DNA synthesis and mitosis were measured at 6 A.M.' 10 A.M., 2 P.M., 6 P.M., 10 P.M., and 2 A.M. in bone marrow of male Swiss Webster mice maintained on a 12-hour light, 12-hour dark cycle (lights on at 7 A.M.). Peak levels of DNA synthesis occurred at 10 P.M. and mitotic peak levels at 2 A.M., coinciding with previously observed peaks of total-body radiosensitivity following 800 and 900 R. Large numbers of cells in a critical organ in radiosensitive life-cycle stages may account for the lowered tolerance of radiation at these times.