Histopathologic Examinations Of Rats Treated By Chronic Inhalation Exposures To Glass Fibers

Abstract

Effects on rats of a chronic inhalation exposure to glass fibers were examined histopatho-logically with special reference to pulmonary fibrosis and tumor genesis. Twenty-seven male Wistar rats of 6 wk of age were exposed to glass fibers, the exposure concentration was 2.2 ± 0.6 mg/m³, and the mass median aerodynamic diameter 2.6 mm (the geometric standard deviation 1.9), for I yr. Among them 6 and 9 rats were sacrificed just after the 1-yr exposure period and after a further l-yr clearance period, respectively. Among 25 control rats who did not undergo the exposure, 5 and 15 rats were sacrificed at the same time as each exposure group. Twelve exposure and five control rats died during the exposure and clearance period, respectively. No tumors were found in both the exposure and control rats immediately after the inhalations. There were no pneumoconiotic nodules or interstitial fibrosis in any of the rats, though a somewhat shorter survival was observed in the exposure group than in the control group. As for the group after the clearance period, increasing macrophages aggregated around the terminal bronchioles and a small number of lung tumors; (or example, two adenomas in the exposure group, and one adenoma and one squamous-cell carcinoma in the control group were noted. Sporadic tumors in other organs were also noted. However, there was no significant difference in the occurrence of these tumors between the exposure and control groups. It was concluded that the chronically inhaled glass fibers showed no apparent promoting effects of lung fibrosis or tumor genesis in this study, although a cumulative survival rate was somewhat more diminished in the exposure group than in the control.