Deposition of Cigarette Smoke Particles in the Rat

The fractional deposition of cigarette smoke particles in the respiratory tracts of rats was studied. Male and female rats were conditioned in nose-only exposure tubes 25 min/day for 2 days, exposed to cigarette smoke at mass concentrations of 95 or 341 mg/m3 25 min/day for 3 days, and then exposed to smoke at mass concentrations of 212 and 657 mg/m3, 25 min/day for 5 days. Mainstream cigarette smoke was generated by a modified Walton smoking machine from two 1R3 research cigarettes burned sequentially for each exposure. Deposition studies were conducted by placing the rats in plethysmograph tubes to allow respiratory minute volume measurements during exposure, then exposing them to [14C] cigarette smoke at mass concentrations of 202 or 624 mg/m3 for 25 min, using the same smoking machine. Size distribution, real-time concentration, and 14C activity of the smoke particles were determined using a multijet Mercer impactor, a real-time aerosol monitor, and filter samples, respectively. Immediately after the exposure, the rats were terminated to determine the distribution of the 14C. Individual lung lobes, trachea and lobar bronchi, head, larynx, kidneys, liver, gastrointestinal (GI) tract, blood, and depelted carcass of each rat were analyzed for 14C content. Results showed that the GI tract contained 16–31% of the total activity, indicating significant clearance from the large airways and nose to the GI tract during the exposure and during the 10–15 min between the cessation of the exposure and the removal ofthe organs. Total deposition of the inhaled 14C activity was 20.1 � 1.6% for both exposure concentrations. The intrapulmonary deposition fractions (lung lobes plus airways below the lobar bronchi) were 12.4 � 0.9 and 15.9 � 1.4% for concentrations of 202 and 624 mg/m3 respectively, suggesting a slight enhancement in upper airway deposition for animals exposed to the higher smoke concentration.