Centriacinar alterations in lungs of cats chronically exposed to diesel exhaust

This study describes the morphologic changes in the centriacinar regions of lungs following long-term exposure of cats to diesel exhaust. Nine male cats (13 months of age) from a minimal disease colony were exposed to diesel exhaust for 8 hours/day, 7 days/week for 27 months. Eight cats were exposed to filtered air. Following exposure, the animals were killed by exsanguination and the lungs and trachea removed from the chest by thoracotomy, weight, and fixed via tracheal cannula with glutaraldehyde/paraformaldehyde (550 mOsmoles, pH 7.4) at 30 cm of pressure. Centriacinar regions were selected from fixed tissue, the airways bisected, and complementary tissue halves processed by a large block method for high resolution light microscopy and for scanning electron microscopy. Compared with controls, diesel-exposed cats had lower fresh lung and kidney weights and lower fixed volumes of the right cranial lobe. The volume fractions of pulmonary parenchyma and nonparenchyma were unchanged. Epithelium of terminal and respiratory bronchioles in exposed cats consisted of three types of cells (ciliated, basal, and Clara cells), compared with only one type (Clara cells) in controls. Carbon-laden macrophages were found filling alveolar and interstitial spaces in exposed animals. Type 2 pneumocyte hyperplasia was present in proximal interalveolar septa. More distal alveolar ducts and the majority of the rest of the parenchyma were unchanged from controls. We concluded that exposure to diesel exhaust produces changes in both epithelial and interstitial tissue compartments and that the focus of these lesions in peripheral lung is the centriacinar region where alveolar ducts join terminal conducting airways.