Ultrastructural changes in hamster lung four hours to twenty‐four days after exposure to elastase

A single endotracheal instillation of elastase initiates a series of changes in animal lungs that results in a condition resembling human panlobular emphysema. An ultrastructural examination of this series of changes was conducted on the lungs of male golden hamsters exposed to 3H-methylated pancreatic elastase and sacrificed at intervals between 4 hour and 24 days after exposure to enzyme. Lung tissue between 4 and 48 hours showed evidence of hemorrhage and progressive degradation of elastic fibers. Very little indication of epithelial cell damage accompanied these changes. Four days after exposure to elastase, synthesis of new elastic fibers began with the appearance of small clumps of microfibrils in close association with interstitial cells, fibroblasts, and smooth muscle cells. There was also evidence of alterations in alveolar type II cells at this time. Small fibrillar elastic fibers continued to be present in the lung through twenty-four days and may represent a slow repair process or may indicate a structural difference in elastic fibers synthesized after exposure to elastase. Evidence of the continued degradation of elastic fiber could be found up to 16 days after exposure to elastase, revealing that repair processes were occurring in some areas of the lung while destructive process still predominated in other areas.