COMPARISON OF PLEURAL RESPONSES OF RATS AND HAMSTERS TO SUBCHRONIC INHALATION OF REFRACTORY CERAMIC FIBERS

In the present subchronic study, we compared pleural inflammation, vis ceral pleural collagen deposition, and visceral and parietal pleural m esothelial cell proliferation in rats and hamsters identically exposed to a kaolin-based refractory ceramic fiber, (RCF)-1 by nose-only inha lation exposure, and correlated the results to translocation of fibers to the pleural cavity. Fischer 344 rats and Syrian golden hamsters we re exposed to 650 fibers/cc of RCF-1, for 4 hr/day, 5 days/week for 12 weeks. Following 4 and 12 weeks of exposure, and after a 12-week reco very period, pleural lavage fluid was analyzed for cytologic and bioch emical evidence of inflammation. Visceral and parietal pleural mesothe lial cell proliferation was assessed by immunocytochemical detection o f bromodeoxyuridine incorporation. Pleural collagen was quantitated us ing morphometric analysis of lung sections stained with Sirius Red. Fi ber-exposed rats and hamsters had qualitatively similar pleural inflam mation at each time point. Mesothelial cell proliferation was more pro nounced in hamsters than in rats at each time point and at each site. In both species, the mesothelial cell labeling index was highest in th e parietal pleural mesothelial cells lining the surface of the diaphra gm al each rime point. Hamsters but not rats had significantly elevate d collagen in the visceral pleura at the 12-week postexposure time Fei nt. Fibers were found in the pleural cavities oi both species at each rime point. These fibers were generally short and thin. These results suggest that mesothelial cell proliferation and fibroproliferative cha nges in the pleura of rodents following short-term inhalation exposure are associated with fiber translocation to the pleura and may be pred ictive oi chronic pleural disease outcomes following long-term exposur e.