Changes in chromosomes of bone marrow after intravenous injections of 7,12-dimethylbenz(a)anthracene and related compounds.

Multiple intravenous injections of an emulsion containing 7,12-dimethylbenz(a)anthracene (DMBA) or 7,8,12-trimethylbenz(a)anthracene (TMBA) induce a high incidence of leukemia in rats. Twenty-four hours after a single injection, about half of the metaphase cells in the marrow have chromosomes with breaks. Although breaks were inflicted on chromosomes of various sizes and morphology, these aberrations were nonrandom in that members of the nos. 1 and 2 chromosome pairs were involved to an extent greater than expected on the basis of their size and number. Distinctive karyotypic abnormalities involving the no. 2 chromosome were observed in half of the leukemic rats, whereas these abnormalities were not observed in nonleukemic, DMBA-treated rats. Benzo(a)pyrene and benzo(e)pyrene, polycyclic aromatic hydrocarbons which did not induce leukemia, produced fewer breaks of the no. 2 (and other) chromosomes than did DMBA or TMBA.