Lung changes resulting from intraperitoneal injections of porcine pancreatic elastase in suckling rats.

We administered 1 mg of purified porcine elastase per 100 g body weight intraperitoneally twice weekly to male rats during the first 4 wk of life. This altered the structure of the lungs so that the proportion of alveolar duct air (the "core" of air internal to the mouths of alveoli in alveolar ducts) increased and the proportion of alveolar air decreased. The alveolar surface-to-volume ratio was decreased, and the lungs had too few alveoli. The lungs were also hyperexpandable, containing more air and saline per gram of lung tissue. No biochemical alterations were noted in elastin or collagen content in elastase-treated animals. In a separate experiment, we showed that elastaselike activity appears in the blood 1 h after intraperitoneal injection of elastase and, although low, was still significantly raised 24 h after injection. We feel that elastase has interfered with lung growth and alveolar development by altering mainly the elastin in the collagen-elastin network. Intraperitoneal elastase injection at the time of active elastin synthesis and alveolar multiplication may be a suitable model to test the hypothesis that lungs injured in infancy may be more susceptible to damage in later life.