Different susceptibility of BALB/Mo and BALB/c mice to cytogenetic damage induced by urethan.

The urethan-induced clastogenic effect in BALB/Mo mice carrying the Moloney murine leukemia virus (M-MuLV) as an endogenous retrovirus was evaluated by short-term micronucleus assay on bone marrow polychromatic erythrocytes (PCE). A single urethan injection in 3 dose levels brought the incidence of micronucleated PCE far above baseline values when scoring was performed 24 h after treatment; this increase was higher in BALB/Mo than in M-MuLV-free BALB/c mice. In a second experiment, micronucleated PCE incidence was determined as a function of the time interval after a single injection of 1 mg urethan/g of body weight. Higher values of micronucleated PCE were scored in BALB/Mo than in BALB/c mice; statistically significant differences were found at 24 and 48 h after treatment.