Mutation induction by N-propyl-N-nitrosourea in eight MutaMouse organs

As a part of the 2nd Collaborative Study for the Transgenic Mouse Mutation Assay, we studied the organ specificity and the temporal changes in mutant frequency (MF) of the lacZ gene following intraperitoneal injection of 250 mg/kg N-propyl-N-nitrosourea into male MutaMouse. We used a positive selection system and examined eight organs, i.e., bone marrow, liver, kidney, lung, spleen, brain, heart, and testis. The chemical caused a significant increase in MF in all organs except for brain, and the bone marrow was the most sensitive organ, exhibiting a MF on day 7 that was 10 times that of the control. The MF increased from day 7 to day 28 in liver, kidney, and testis, while it decreased in bone marrow. The relationship between the results of this study and the target organs of carcinogenesis, and the cause of the temporal changes in MF, are discussed.