Pathophysiology of experimental canine interstitial lung disease.

may be present long before they are clinically apparent. Classically, pulmonary complications become apparent only about a week after paraquat ingestion, but lesions are regularly apparent in animals long before this. At present, it is still not clear from our data whether the airway epithelium is involved or not and we are studying the matter further. As noted, rather nonspecific alterations were seen in some paraquat animals, but not in all of them, and it is clear that airway epithelium shows lesions which, if real, are far less obvious than those seen in alveolar epithelium. Absence of lesions in airway epithelium would be of considerable interest. It is not clear why certain organs and cells are particularly sensitive to paraquat. The similarity to oxygen poisoning and the additive effect of oxygen to paraquat poisonings has suggested that paraquat may particularly affect the lung because of its high ambient oxygen. Were this the case, then airway epithelium should be especially involved but this is not the case. Alternatively, cells may be particularly sensitive because paraquat goes selectively to them. This is a hard question to solve in the lung interstitium where the epithelium appears sensitive and the endothelium relatively resistant. Paraquat is highly soluble in water and thus ordinary autoradiographic techniques cannot be used and, in addition, high resolution is necessary to separate endothelium from epithelium. However, the presence or absence of radioactive paraquat in airway epithelium should be relatively easy to determine and we are at present examining this problem.