Pulmonary and Pleural Responses in Fischer 344 Rats Following Short-Term Inhalation of a Synthetic Vitreous Fiber: I. Quantitation of Lung and Pleural Fiber Burdens

The pleura is an important target tissue of fiber-induced disease,although it is not known whether fibers must be in direct contactwith pleural cells to exert pathologic effects. In the presentstudy, we determined the kinetics of fiber movement into pleuraltissues of rats following inhalation of RCF-1, a ceramic fiberpreviously shown to induce neoplasms in the lung and pleuraof rats. Male Fischer 344 rats were exposed by nose-only inhalationto RCF-1 at 89 mg/m³ (2645 WHO fibers/cc), 6 hr/day for 5 consecutivedays. On Days 5 and 32, thoracic tissues were analyzed to determinepulmonary and pleural fiber burdens. Mean fiber counts were22x10⁶/lung (25x10³/pleura) at Day 5 and 18x10⁶ (16x10/pleura)at Day 32. Similar geometric mean lengths (GML) and diameters(GMD) of pulmonary fiber burdens were observed at both timepoints. Values were 5 µm for GML (geometric standard deviationGSD 2.3) and 0.3 µm for GMD (GSD 1.9), with correlationsbetween length and diameter () of 0.2–0.3. Size distributionsof pleural fiber burdens at both time points were approximately1.5 µm GML. (GSD 2.0) and 0.09 µm GMD (GSD 1.5; 0.2–0.5). Few fibers longer than 5 µm were observedat either time point. These findings demonstrate that fiberscan rapidly translocate to pleural tissues. However, only short,thin (<5 µm in length) fibers could be detected overthe 32-day time course of the experiment.