Species comparisons of proximal alveolar deposition patterns of inhaled particulates.

Previous studies have shown that inhaled particles and fibers that are small enough to pass through the conducting airways deposit preferentially at alveolar duct bifurcations in the distal lungs of exposed rats. Because it is well documented that anatomic and physiologic differences exist among common experimental animals that may influence deposition patterns, we compared inhaled particle deposition patterns in alveolar regions of four rodent species. Proximal alveolar regions of hamsters and guinea pigs contain rudimentary respiratory bronchioles, whereas in rats and mice, terminal bronchioles lead directly into alveolar ducts. Groups of animals from one strain each of rats, mice, hamsters, and guinea pigs were exposed to aerosols of carbonyl iron (CI) particles for 1 h at design concentrations of 100 mg/m3. Immediately after exposure, the lungs of sham- and CI-exposed animals were perfusion fixed through the vasculature. Subsequently, lung tissues from exposed animals was analyzed for iron concentration; data indicated that total lung deposition of iron particles was highest in mice and hamsters. In addition, scanning electron microscopy of dissected lung tissue revealed that particle deposition patterns in the proximal regions of the distal lung were similar for all species, although greater numbers of CI particles per bifurcation were deposited in rats and mice compared to hamsters (p less than 0.05) and greater numbers were deposited in hamsters compared to guinea pigs (p less than 0.05). The data suggest that the presence of undeveloped respiratory bronchioles in the lungs of hamsters and guinea pigs has little influence on distal lung particle deposition patterns. It remains to be determined whether inhaled particles are deposited at similar sites in the lungs of species with well-developed respiratory bronchioles such as cats, nonhuman primates, and humans.