Inhalation toxicity studies on cigarette smoke (VI). 6-week comparative experiments using modified flue-cured cigarettes: histopathology of the lung.

Rats were exposed twice daily for 6 weeks to diluted smoke derived from cigarettes with a range of deliveries of particulate matter. The inhaled smoke reached the alveolar surface, increased the size and number of free macrophages and provoked epithelial metaplasia but did not appear to alter the lymphoid reaction to spontaneous infection. The hypertrophy of the macrophages was typically alveolar and their hyperplasia was directly proportional to the particulate delivery of cigarettes smoked. Alveolar metaplasia was incipient, developed characteristically near the respiratory bronchiole in close association with macrophage clusters and only in rats exposed to smoke from cigarettes with the highest delivery of particulate matter.