Comparative subchronic inhalation study of smoke from the 1R4F and 2R4F reference cigarettes.

A subchronic, nose-only inhalation study compared the effects of mainstream smoke from a 1R4F research cigarette to that of a 2R4F research cigarette. Male and female rats were exposed for 1 h/day, 5 days/wk, for 13 wk to mainstream smoke at 0, 0.06, 0.20, or 0.80 mg wet total particulate matter per liter of air. Clinical signs, body and organ weights, clinical chemistry, hematology, carboxyhemoglobin, serum nicotine, pulmonary plethysmography, gross pathology, and histopathology were determined. When histological changes resulting from exposure to smoke from the two types of cigarettes were compared, no biologically significant differences were observed. At the end of the exposure period, subsets of rats from each group were maintained without smoke exposures for an additional 13 wk (recovery period). At the end of the recovery period, there were no statistically significant differences in histopathological findings observed between the 1R4F and the 2R4F cigarettes. The complete toxicological assessment in this comparative inhalation study of 1R4F and 2R4F cigarettes suggests no overall biologically significant differences between the rats exposed to the two cigarettes.