PULMONARY AND PLEURAL RESPONSES IN FISCHER-344 RATS FOLLOWING SHORT-TERM INHALATION OF A SYNTHETIC VITREOUS FIBER .1. QUANTITATION OF LUNG AND PLEURAL FIBER BURDENS

The pleura is an important target tissue of fiber-induced disease, alt hough it is not known whether fibers must be in direct contact with pl eural cells to exert pathologic effects. In the present study, we dete rmined the kinetics of fiber movement into pleural tissues of rats fol lowing inhalation of RCF-1, a ceramic fiber previously shown to induce neoplasms in the lung and pleura of rats. Male Fischer 344 rats were exposed by nose-only inhalation to RCF-1 at 89 mg/m(3) (2645 WHO fiber s/cc), 6 hr/day for 5 consecutive days. On Days 5 and 32, thoracic tis sues were analyzed to determine pulmonary and pleural fiber burdens. M ean fiber counts were 22 X 10(6)/lung (25 X 10(3)/pleura) at Day 5 and 18 X 10(6)/lung (16 X 10(3)/pleura) at Day 32. Similar geometric mean lengths (GML) and diameters (GMD) of pulmonary fiber burdens were obs erved at both time points. Values were 5 mu m for GML (geometric stand ard deviation GSD approximate to 2.3) and 0.3 mu m for GMD (GSD approx imate to 1.9), with correlations between length and diameter (tau) of 0.2-0.3. Size distributions of pleural fiber burdens at both time poin ts were approximately 1.5 mu m GML (GSD approximate to 2.0) and 0.09 m u m GMD (GSD approximate to 1.5; tau approximate to 0.2-0.5). Few fibe rs longer than 5 mu m were observed at either time point. These findin gs demonstrate that fibers can rapidly translocate to pleural tissues. However, only short, thin (<5 mu m in length) fibers could be detecte d over the 32-day time course of the experiment. (C) 1996 Society of T oxicology