Document gbgR3oLV3p44kVM5RZpBmvGk9

Ref.: / XIVth International Congress of Occupational Health, Madrid, Sept. 16-21, 1965 Vol. II. International Congress Series 62 Excerpta Medica Foundation. U\l>KkiV.L.Vi'AL AhULSTOSlO IN GUINEA 1>1CS P. F. HOLT and J. MILLS University of Reading, dcrkslurc, Great Britain A description of changes in the lungs of rats which had inhaled very fine chrysolite asbestos oust has been publislicd (Holt, Mills and Yount. 1963). Severe lesion* developed a few week* after the dust was inhaled, ye: few particles of asbestos were Visi ble in sections. By dark tround illumination, areas were visible in these sections where dust particles ihai wcie too small to be observed by transmuted light were attretated. In human asbestosis, tile lunts contain many asbestos fibres up to *0/x and somo even lonter, and also asbestos bodies, which are fibres coated with protein. Few fibres and no bodies were visible when the sections of rai lungs were viewed in the optical microscope. Apparently the respi ratory passages of the rat are capable of removing front the air nearly all particles of dust larger th.ui about a micron, and this may account for the difference between asbestosis as sees is the rat and in the human lung. This paper reports experiments on guinea-pigs which had been caused to inhalo Cite particles of asocstos. A dense dust cloud was established by using a modification (Holt, Mills and Young, 1964) of an apparatus previously described (Holt and Young, 1960). The dust contained many par ticles less than 1 fi long. - Tnc same damage was observed as in the lungs of rats, but the guinea-pig lungs have numerous panicles of asbestos which are longer than * micron and also typical beaded and non-beaded asbestos bodies. Early sections are characterised by large mononuclear macrophages which are filled with dust panicles and multinuckar giant ceils lying in a rctieulin mesh. Croupe of macrophages become enclosed by a delicate enllagrn capsule and bier collagen replaces rctieulin in the substance of the nodule. The giant edit which are so obvious ia the early soctions, become less frequent after a few months. In one experiment guinea-pigs were exposed to a dense dust cloud over a period of only two weeks and woe then removed from the dusting tunnel. Animals were killed at intervals and cliangcs in histological soctions of the lungs were Studied. An unimal was killed on Uie 7tli day of ex posure to crocidoiitc dust. A soeuon of the lungs (Fig. 1) shows a terminal bronchiole plugccd with cellular exudate which was pouring uuo the respiratory bronchiole. This exudate consisted main ly of maeroph.iges, many of which were mulunucleaicd and loaded to capacity with fine dust. An occasional dust-laden cell or short asbestos fibre occurred in the alveolar duet. The initial lesion then appears to be a bronchiolitis, with an extension along the respiratory bronchiole srd alveolar duct. Another guinea-pig was killed 190 days after the experiment started. Histological sections show severe damage to the terminal bronchiole and to the air spaces bordering the respiratory bron chioles. Tiic alveolar duels are still idled with cellular exudate which contains many macrophages loaded to capacity with line dust. Asbestos bodies and asbestos fibres are numerous. An animal killed 400 days after a' similar ex posure to chrysolite dust bad extensive fibrosis*'* around tlio terminal bronchioles, Tbs fibrosis diminished progressively along the alveolar duets into alveoli more remote from the bronchioles (Fig. 2). Lung sections which had been ucaiad with ferrocyamdc showed asbestos bodies stained blue, in dicating the presence of iron in tho protein ooating (Fig. 3). The very small dust particles which packed tho macrophages also appeared blue at higher magnification. Somo of the fibres whieh penetrated into the lung were of considerable length. In one animal killed 193 days after exposure to croeidolitc, an asbestos fibre traversed ibo whole of one al veolus, penetrating the wall and extending into an adjacent alveolar duet. This fibre .was not uni formly coated. Sdver impregnation showed one 467 DUP 1141932 t. T. BOLT AMO 1. MlU-i Fit. I. Section of the hint of e guinea-pig killed after inhaling erecidolite asbestos dust for SO houn during 7 days. A terminal bronchiole is plugged with cellular exudate which is pouring into the respiratory bronchiole. Macrophages filled with dust are in the exudate and occa sionally in the wall of the duct. (X 17S Hacmaioxylin-eosin). and to be heavily coated by some substance which greatly increased its thickness and which stains intensely. At the other end was a similar but lighter eoating and in the middle, where the fibre penetrated the alveolar wall, there was acareely any eoating; the fibre was much thinner end yellow. This fibre also traverses a group of eioeely packed yellow granules which represent the lead of due carried by e macrophage, the cell it self remaining unstained by this technique. Other fibres presented a beaded appearance and were stained heavily with silver. A short fibre nearby was unstained and appeared as a very fine enoostod filament. One fibre was unstained but appeared beaded and another had two black beads at one end, a thin, curved and unstained middle portion and a black bead at '.he other end. There wide variations in the size, shape, thickness and staining properties of asbestos fibres, alt of which had been in the lung for approximately the same time (between 195 and 111 days) were inexplicable. All the silver impregnated sections exhibited a dilTure retkulinosis of the alveolar walls. The remits of these experiments on guinca-pics confirm the general findings resulting from the previous experiments on rats. The principal con- 661 DUP 1141933 fiXP&UMLKTAL ASttCSTOSU IN GUINEA PICS 1 I I1 I Fiu, 2> Section of the lung of u guinea-pig killed 390 Jay* after inhaling chrysotik usbotios for 14 Cays. A laic u&ge of bronebiobtu wuh collagen infiltration m the surrounding alveoli. (X 40 Van Gkaon). Fig. 3. Guinea-pig killed 181 day* after inhalation period of 14 day*. CrociUolile aaheaUM. Asbeatoe bodks namod deep blue indicate iron in the protein coating, borne fibres are not coatod. Suboucroa asbnuot ?*rt*i~* ^ pbagocyioa turn blue. (X 200 Hacnuiioayiuv^eain and Perl). 669 DUP 1141934 ":i_______ "-HE* - f^tw4' 'H '1 'O'Bljtp f. P. HOLT ISO J, WILLS elusion resulting from our earlier work, that very fine particles of asbestos, even submieroscopic panicles, can rapidly produce severe lesions in the lung, is reinforced. -The dilTcrencc between the lungs of the experimental rats and those of the guinea-pigs may be due to differences in the respiratory tract whereby the rat can efficiently remove from inhaled air panicles down to a sire of 1 ft or even less. In some earlier publications emphasis has been laid on the importance of long asbestos fibres as the causative agent in asbestosis. Our results indicate that very small asbestos panicles can cer tainly cause widespread damage in the lungs of small animals and this fraction of the dust can not be ignored in the assessment of a hazard. The fact that the diameter of the ultimate fibres of the types of asbestos which tire used in industry is smaller than the limit of resolution of the op tical microscope indicates that electron as well as light microscopy should be used in the study of this hazard. ACKNOWLEDGEMENTS This paper describes pan of a programme of re search which is being carried out under the aus pices of the Asbestosis Research Council. The authors are indebted to Mr. K. A. Jerrome for technical assistance. REFERENCES Holt, P. P,, Mills, J. and Youno, D. K.t Fort. Khrlut der Sumhlungcnlonchunt. edited Rcploh. H. and KlosterkStter, W. 1963 (201), Nioderrheiniaclie Druckcrci. Holt, P. F- Mills. J. and Youno, D. K.: J. Fath. Bad. 1964, S7 (15). Holt, P. F. and Youno, D. K.: Ann. occur. Uys I960, 2 (249). Ucwmcn, Abstract, Rfcaimc, Vol. IV, No. 170 670 DUP 1141935