title: Induction of long-lived chromosome damage, as manifested by sister-chromatid exchange, in lymphocytes of animals exposed to mitomycin-C.
abstract: The cytogenetic effects of repeated vs. acute exposure to a chemical mutagen--carcinogen were determined with an in vivo system in which chemicals injected into rabbits induce sister-chromatid exchanges (SCEs). SCE induction can be monitored when the animal's peripheral lymphocytes are cultured in the presence of bromodeoxyuridine (BrdUrd) and then scored for SCE frequency. Mitomycin-C (MMC), 0.5 mg/kg, was injected intraperitoneally once a week for 8 weeks. This treatment initially induced small increases in SCE frequency within one day of injection, followed by a return to control levels within 1 week. After the 4th injection, however, the frequency failed to return to normal. After the 5th injection, however it showed a 4-fold increase over the control which was sustained for the remaining 3 weeks of treatment and for an additional 2 weeks thereafter. The frequency then dropped to twice the control value and remained at this level for more than 4 months. All of the high SCE values after the first 4 weeks were due in part to the appearance and persistence of a population of cells with high SCE frequencies. Exposure to the same total dose given as a single injection resulted in a transient elevation in the SCE frequency and a subsequent return to lower values, with no evidence of a delayed effect such as the increase observed after 4 weeks in repeatedly exposed animals. Overall, repeated exposure is at least as effective as acute exposure in eliciting long-lived SCEs in vivo.
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002869:Chromosome Aberrations; D002875:Chromosomes / Q000187:drug effects*; D003434:Crossing Over, Genetic; D004305:Dose-Response Relationship, Drug; D008214:Lymphocytes / Q000648:ultrastructure; D008297:Male; D008937:Mitomycins / Q000494:pharmacology*; D011817:Rabbits; D013997:Time Factors
chemical_list: D008937:Mitomycins