Daily variation in radiosensitivity of circulating blood cells and bone marrow cellularity of mice.

Random bred, nocturnal, male Mus musculus (DUB-ICR), on a 12/12 light/dark cycle with lights on at 6 a.m., were exposed to 100 R or 200 R of X-radiation at either noon or midnight to study diurnal radiosensitivity in circulating blood cells and bone marrow cellularity. Hematocrits, reticulocyte and white blood cell counts, daily white blood cell rhythm, and bone marrow cellularity indicate that these mice are more radiosensitive at night. At low doses it is possible that diurnal rhythms in natural, biological radioprotectors such as corticosterone may have more influence on radiation sensitivity than mitotic activity.