6-MONTH EXPOSURE OF STRAIN A J MICE TO CIGARETTE SIDESTREAM SMOKE - CELL-KINETICS AND LUNG-TUMOR DATA/

Male strain A/J mice were exposed to sidestream smoke (SS) generated f rom burning Kentucky 1R4F reference cigarettes. Chamber concentrations were 4 mg/m(3) of total suspended respirable particulate matter (TSP) . Animals were exposed 6 hr a day, 5 days a week. One-week cumulative labeling indices were significantly increased in the large intrapulmon ary airways during the Ist week and in the respiratory epithelium of t he nasal and maxillar turbinates during the first 3 weeks of exposure and then returned to control values. Subsequently, signs of increased cell proliferation were again found in the nasal and maxillar turbinat es during the 9th and 16th exposure weeks. The experiment was terminat ed after 6 months. The number of animals bearing lung tumors was the s ame in smoke-exposed as in filtered air-exposed animals as was the ave rage number of tumors per lung. Analysis of the DNA of individual tumo rs obtained from exposed and control mice for K-ras mutations suggeste d that exon 2 might be a specific target for SS. It was concluded that (1) duration of exposure was too short or (2) concentration of TSP wa s too low to reveal a possible carcinogenic potential of SS in strain A/J mice or that (3) SS is not carcinogenic in strain A mice. (C) 1995 Society of Toxicology.