Strand breakage in rat liver DNA and its repair following administration of cyclic nitrosamines.

the velocity sedimentation of DNA prepared 4 hr after administration of from 1to 100mg/kg body weight nitroso morpholine were observed in both alkaline and neutral su crose gradients. The single-strand damage to DNA was not completely repaired 14 days after treatment while the double-strand breaks were more rapidly repaired. Injec tion of similar doses of either of the other two cyclic com pounds also caused single-strand breaks in liver DNA which required at least 6 days for repair. These compounds had no effect on the velocity sedimentation of DNA on neutral sucrose gradients. High doses of the respective parent cyclic amines, morpholine, piperidine, and piperazine, did not cause strand breaks in DNA. The data are discussed with particular reference to the possibility that the cyclic nitrosamines examined may be metabolized by rat liver with the formation of species capable of alkylating DNA.