Persistence of micronuclei in peripheral blood normochromatic erythrocytes of subchronically benzene-treated male mice.

The kinetics of micronucleus (MN) induction and decline in blood normochromatic erythrocytes (NCE) of mice subchronically exposed to benzene was investigated during and after exposure. Swiss (ICR) male mice (10/group) were given 0.0, 36.6, 73.2, and 146.4 mg/kg body weight benzene by gavage daily for 14 days, except for days 5 and 10. The frequency of MN increased significantly (P less than .001) during benzene treatment as a function of both concentration and time. Eleven days after exposure the levels of MN were higher than those observed at the end of exposure. After an initial rapid decline in the frequency of MN from 11 to 18 days postexposure, the decline became linear with time through 60 days postexposure. Using linear regression analysis, the MN level in each treatment group was predicted to reach control levels by approximately 85 days post-treatment. Dose-dependent suppression and recovery of erythropoiesis, estimated by polychromatic erythrocyte frequency, were observed in the 1st and 2nd weeks of exposure, respectively. Red blood cell (RBC) production was markedly increased in the first 3 weeks after benzene treatment. At later times the rate of production of the RBC returned to normal and may account for the linear decline observed in MN frequency. This research indicates that the frequency of MN is dose and duration dependent, while the decline in MN frequency after the end of benzene exposure can be related to changes in the kinetics of erythropoiesis.