Time-course analysis of type II cell hyperplasia and alveolar bronchiolization in rats treated with different particulates

In this study, we compared the morphological reaction patterns in rat lungs following a single intratracheal instillation of 20 mg quartz, 20 mg coal mine dust (15.3% quartz), or 25 mg talc. Control animals received a single dose of 0.5 mi saline solution intratracheally. Investigations by light mic roscopy, morphometry, and DNA image cytometry were carried out 3, 6, 12, an d 18 mo after dust administration. During the investigation period, we obse rved a temporary increase in the number, area, and proliferative activity o f the type II cells, which differed in intensity among the three dusts. Aft er 18 mo, however, type II cells in treated animals did not differ from con trol animals. On the other hand, the expansion of a multifocal alveolar bro nchiolization as putative preneoplastic lesion had progressed enormously by the end of the rest (1-3% of the investigated lung area). Consistent with this, the proliferative activity of the epithelial cells in terminal bronch i of the coal mine dust- and quartz-treated animals was enhanced by the end of the 18-mo investigation period, while the reaction to talc was minimal (0.2% of totally investigated lung area). Our data suggest that in bronchio lo-alveolar regions, especially in the epithelium of terminal bronchi, ther e is an overshoot regeneration after cell damage that leads to an alveolar bronchiolization.