Document pJ994ZG1Kv6moawbq3kXrvKB

EFFECTS OF INHALATION OF ASBESTOS IN RATS 257 j ffuse interstitial fibrosis with gradual in- adenomatosis. In contrast to this, a few <*1 se in the density of the fibrous tissue, control animals were seen to have solitary Ornately resulting in the replacement of adenomata which were small in size. The most of the lung parenchyma by a dense adenocarcinomata were of the same type llaeen network surrounding distorted air and origin as the " alveolar adenocarcino ''wees, many of which contain large clumps mata " described by Shabad and Pylev granular pneumocytes which, in some (1970); many of these tumours were papillary jreas have lysed leaving foci of lipo-alveolar adenoma-carcinomata. The squamous car cinomata appeared to originate from foci ^The assessment of these lesions was of squamous metaplasia occurring in the luised on 4 grades of fibrosis--minimal, asbestotic lesions in the respiratory bron slight, moderate and severe. Typical ex chioles (Fig. 7, 8). As far as can be ascer amples of slight, moderate and severe tained, all these tumours were peripheral Hshcstosis are shown in Fig. 1-4. In addi- in origin and not bronchial papillomata. liirn, when carrying out the assessment it The classification of these tumours was rt-as found convenient to introduce the discussed in some detail in Session VI at intermediate categories minimal/slight, slight/ the Gatlinburg Conference on the Morphology moderate and moderate/severe. The 7 re of Experimental Respiratory Carcinogenesis sulting categories were scored 2-8 and the in 1970; and the chapter by M. F. Stanton normal lung, in which there was no sign of (1974) in the IARC Monograph on Pathology ashestosis, was scored 1, and the assessments of Tumours in Laboratory Animals contains were averaged for each group of rats. The detailed descriptions of the tumours that we repeatability of this form of assessment was have illustrated. rested on 154 sections, reassessed in a The rats used in this experiment are different random order and 90% were from a caesarean derived, barrier maintained assigned to within one category of the first colony and fortunately they have been kept reading. free of rat bronchitis; therefore the squamous Classification of tumours.--The tumours metaplasia was not associated with bronchi found in the lungs of rats after exposure to ectasis. the various types of asbestos dusts were Metastases in the thoracic cavity to the peripheral adenomata, widespread adeno chest wall, diaphragm, pericardium or the matosis, adenocarcinomata and squamous tracheo-bronchial lymph glands were seen carcinomata. The rarity of pulmonary tu in 14 animals; the majority had lesions mours in rats has been stressed in the invading 3 of the sites and in only 2 animals reviews by Kuschner and Laskin (1970) and were metastases observed in the tracheo Xliabad and Pylev (1970). Further, these bronchial glands. In one animal secondary authors have described the development and deposits were seen in sections from a kidney. morphological features of the tumours that Eight adenocarcinomata and 6 squamous we are reporting. All these tumours were tumours had metastasized. peripheral and appeared to arise from the region of the respiratory bronchioles in which the asbestos fibre had accumulated. The origin of the adenomata appeared to be from accumulation of type II epithelial cells that proliferated in the alveoli of the RESULTS All except 2 of the rats in the groups with exposure of 12 months or less survived for the whole of their planned respiratory bronchioles (Fig. 5, 6). In many exposure. In the 24-month group there of the exposed animals these tumours were was appreciable mortality before the end multiple, and in a number of animals, of exposure and only 53% survived for particularly those with the more severe grades of asbestosis, there seemed to be adenomata arising from numerous adjoining respiratory bronchioles, giving an impression the full period. Out of 1013 rats it was impossible to obtain adequate histological material in only 8 because of cannibalism. of contiguous adenomata invading large areas of the lung. Dr Harold Stewart Dust retention (personal communication) suggested that The mean weights of asbestos dust this type of lesion should be referred to as in the lungs of animals killed at the