: Glaser, U.; Oldiges, H.; Takenaka, S.

Abstract
Pulmonary changes of 153 male Wistar rats were examined histopathologically after continuous exposure to cadmium oxide dust (CdO) at concentrations of 0, 30 or 90 Myg Cd/cubic meter for a maximum period of 18 months. In the 90 Myg-exposure group, the exposure was terminated at 7 months due to an increase of mortality. Six to 8 animals of each group were sacrificed at 6 months and - with the exception of the 90 Myg-exposure group - at 18 months (sequential sacrifice study). Subsequent to the inhalation period, remaining animals were kept unexposed until the termination of the experiment at 31 months (basic study). At 6 months, animals of both exposure groups inflammatory reactions in the alveolar region. Bronchiolo-alveolar hyperplasia was also observed. In the 90 My g-exposure group the changes were more severe than in the 30 Myg-exposure group. At 18 months, abnormal proliferation of epithelia (nodular formation of mucus-secreting cells, basophilic foci of cuboidal epithelia and adeno matous proliferation of epithelia) occured in the 30 Myg-exposure group in association with the changes observed at 6 months. In the basic study primary lung tumors developed in 72 % of the 30 My g-exposure group and in 31 % of the 90 My g-exposure group. The tumor incidence is obviously dependent on the duration of exposure, which was much shorter in the 90 My g-exposure group. The lung tumors were classified as bronchiolo-alveolar adenomas and adenocarcinomas, benign and malignant squamous cell tumors, and an adenosquamous carcinoma. The types of tumors observed in this experiment were identical to those in duced in a previous experiment using CdCl sub 2 and in a parallel experiment using CdSO sub 4, CdS and CdCl sub 2. The findings of this study suggest that progressive prolifertion of bronchiolo-alveolar epithelia can lead to the development of lung tumors in rats exposed to CdO.