||Stanford Research Inst., Menlo Park, Calif. Life Sciences Div.;National Environmental Research Center, Research Triangle Park, N.C. Div. of Health Effects Research.;National Environmental Research Center, Cincinnati, Ohio. Environmental Toxicology Research Div.
Female beagle dogs were exposed for about 18 months to 1 ppm of ozone in air for either 8, 16, or 24 hours per day and to 2 or 3 ppm for 8 hours a day. The earliest evidence of response was the appearance of macrophages in and around the respiratory bronchiolar-ductal region and in the adjacent alveoli. The macrophages increased with the 'dosage,' the maximum concentrations being associated with 3 ppm for 8 hours per day. Although fibrous tissue elements were only rarely deposited at the lowest dosage, deposition became evident in occasional alveolar ducts following exposure for 16 hours daily to 1 ppm, and increased as the concentration of ozone rose. Features more apparent at the higher concentrations were thickening of the terminal and respiratory bronchiolar walls and their infiltration, by lymphocytes and some plasma cells and 'fibroblasts' that formed peribronchiolar collars of cells. Strands of connective tissue which contributed to the narrow alveolar openings in the respiratory bronchioles and in the alveolar ducts, extended into the attached alveolar walls. Bronchiolar walls, thickened by infiltration with cells and deposition of connective tissue, reduced the caliber of small airways.