Mass and number of fibres in the pathogenesis of asbestos-related lung disease in rats

Abstract

Summary.-Five groups of rats were treated by inhalation for 12 months with the U.I.C.C. preparations of the 3 main commercially used asbestos types, chrysotile, crocidolite and amosite. The experiment was designed so that the effects of both fibre mass and fibre number could be examined. The results indicated that chrysotile dust caused far more lung fibrosis than either amphibole type even when the fibre numbers in the dust clouds were similar. All malignant pulmonary neoplasms found during this study occurred in animals treated with chrysotile. The fibre-number calculations used for the generation of dust clouds were evaluated using the parameters recommended by the Health and Safety Executive in 1976, by which all fibres over 5 ,um long are counted using a phase-contrast light microscope. When fibrelength distributions were calculated using a scanning electron microscope, however, it was found that the chrysotile clouds used in this study contained many more fibres over 20 ,um long than either of the amphibole clouds. The results, therefore, support previous suggestions that long asbestos fibres are more dangerous than short. They also indicate that neither a single mass standard, nor the present fibre-number standards are satisfactory.

Sequence of bronchoalveolar lavage and histopathologic findings in rat lungs early in inhalation asbestos exposure

“…The concentration of asbestos used in this experiment, when inhaled daily for 3 mo or longer, is known to cause fibrosis in rat lungs (Wagner et al, 1974;Holt et al, 1964;Tetley et al, 1976;Davis et al, 1978;Barry et al, 1983;Wagner et al, 1980). Using the same dose for shorter exposure periods of 2, 4, and 6 wk revealed (1) a demonstrable inflammatory and fibrotic process in the terminal airways after 2 wk of exposure (Figs.…”

“…In previous inhalation experiments, the time periods studied have been either very brief (1 h) (Brody et al, 1981) or very long after fibrosis is already evident (3 mo or longer) (Wagner et al, 1974(Wagner et al, ,1980Holt et al, 1964;Tetley et al, 1976;Davis et al, 1978;Barry et al, 1983). In these time periods, increases only in the number of macrophages have been uniformly observed.…”

“…Barry et al (1983) found that after 5 d of daily exposure to 9 mg/m 3 of chrysotile asbestos there was an increase in the number of alveolar macrophages, and the alveolar walls adjacent to terminal bronchioles appeared thickened. Wagner et al (1974), Tetley et al (1976), and Davis et al (1978) each independently showed that rats that inhaled chrysotile asbestos at doses of 10-15 mg/m 3 , 7 h/d, for 15 wk or longer developed fibrosis. This study used daily inhalation of asbestos, at a concentration known to cause fibrosis in rats, for periods of 2, 4, or 6 wk.…”

Distribution of transforming growth factor-beta 1, fibronectin, and smooth muscle actin in asbestos-induced pulmonary fibrosis in rats.

“…A number of animal models for this disease have been studied in which the asbestos exposure has been achieved either by inhalation (Brody and Overby, 1989; Pinkerton et al, 1984; Barry et al, 1983; Davis et al, 1978;Wagner et al, 1974) or by intratracheal instillation (Begin et al, 1981(Begin et al, ,1983; Craighead et al, 1982; Schoenberger et al, 1982). Introduction of asbestos fibers into the lung by either method results in interstitial fibrosis at the junction of the terminal bronchioles and alveolar ducts as is the case in human asbestosis (Begin et al, 1983; Craighead et al, 1982; Selikoff and Lee, 1978; Wagner et al, 1974;Wagner, 1965).…”

The Filtration of Fibrous Aerosols

“…Inhalation of airborne bers may lead to respiratory tract diseases in humans and laboratory animals (International Agency for Research on Cancer 1988;International Program on Chemical Safety 1988;World Health Organization 1984Davis et al 1978;Hesterberg et al 1993;Lippmann 1990;Pezerat et al 1992;Vu 1988;Wagner et al 1974). Respirator lters are designed to remove spherical and brous aerosols upon inhalation.…”