Effect of Exposure Mode on Amounts of Radiolabeled Cigarette Particles in Lungs and Gastrointestinal Tracts of F344 Rats

Abstract

This study was designed to compare the internal and external deposition of cigarette smoke particles in F344IN rats after nose-only or whole-body exposures and to provide information on how grooming affects the amount of smoke particles that pass through the gastrointestinal (GI) tract. Female rats were exposed to mainstream cigarette smoke by - four different modes: nose-only, tube-restrained (NOT); pelt-only, tube-restrained (POT); whole-body, tube-restrained (WBT); and whole-body, cage-housed (WBC). Croups of rats were exposed simultaneously for 40 min by 1 of the 4 modes to [¹⁴C]ldotriacontane (DTC) labeled cigarette smoke at a mean mass concentration of 327 mglm³. Half of the rats from each group were sacrificed immediately after exposure, and the others were sacrificed 24 h later. Head skin, a sample of subcutaneous fat, GI tract, trachea/lobar bronchi, lungs, depelted head, depelted carcass, and remaining pelt were analyzed to determine their ^UC content. About 60% of the ¹⁴C activity in the respiratory tract in the NOT and WBT groups was deposited in the pulmonary region, and about 40% was in the head airways and trachea. The radiolabeled DTC was cleared very slowly from the pulmonary region. The initial total body burdens of ¹⁴C in the rats exposed by the WBT and WBC modes were higher than those in the rats exposed by the NOT mode as a consequence of pelt contamination by the ¹⁴C-DTC. Crooming resulted in the ingestion of about 80-90% and 60% of the ¹⁴C activity originally deposited on the head skin and pelt, respectively, by 24 h after exposure. The ratio of the amount of smoke particles either contained within or passing through the CI tract to the amount in lung after 24 h was 2.6 for WBC-exposed rats and 1.3 for NOT-exposed rats. We concluded that compared to rats exposed using the NOT mode, WBC exposures increased the amount of smoke particles passing into the CI tract by about a factor of two.