Ultrastructural alterations of APUD cells during nitrosamine-induced lung carcinogenesis.

Groups of Syrian golden hamsters were treated twice weekly for life with 1/10 LD50 DEN, or once weekly for life with 1/5 LD50 DBN. The sequential alterations in the ultrastructure of Apud cells in their bronchial lining were examined. Both carcinogens caused pronounced proliferation of this cell type during the initial treatment period. Thereafter, the formation of increasing numbers of filamentous bundles was observed in the cytoplasm of the Apud cells, whereas their neurosecretory granules decreased in number. The present findings suggest that after an initial phase of proliferation, the Apud cells undergo squamous metaplasia when treated with the two nitrosamines investigated.