The in vitro studies showed that organ specific metabolic activation does not appear to play a predominant role for the in vivo activities of the studied nitrosamines 2. The in vivo studies following 1 h exposure of rats with the nitrosamines can differentiate between organs susceptible for genotoxicity and and those which are not. Nontarget organs in carcinogenicity can not be identified exclusively. 3. The additional study of persistence of genotoxicity may identify organs susceptible for carcinogenicity. Presently, we are working on new techniques to detect DNA SSB and other events with microscale methods. This is necessary to allow a more complete elucidation of genotoxicity in remote target organs and with other carcinogens which may not induce DNA SSB. Accordingly in the near future we expect to have even more versatile tools available to study toxicokinetics of foreign compound. Meanwhile our work with N-nitrosamines is continuing in order to better understand their in vivo modes of action and to better evaluate their burden and risk for man.
