Recovery from paraquat pneumonitis.

New Zealand white rabbits were evaluated for recovery from paraquat induced pneumonitis six weeks after the last exposure. The animals were exposed to a respirable aerosol of 100 ml distilled water or 250 mg paraquat in 100 ml distilled water. Blood gases, breathing frequency, and body weights were recorded before and at regular intervals after exposure. Groups included control and two paraquat exposures (separated by a five day interval). Morphometric and pathological measurements were made at death either three days or 42 days after the second exposure. The animals killed three days after the second exposure showed hypoxia, decreased breathing frequency, decreased body weight, increased A-aO2 gradient, decreased per cent macrophages in bronchoalveolar lavage fluid, increased per cent neutrophils in bronchoalveolar lavage fluid, increased lung weight, and reduced lung volume compared with animals allowed to recover. None of these measures differed between control animals and animals allowed to recover, except that animals exposed to paraquat had significantly increased lung volume and lung weights. Pathological changes noted three days after two exposures were no longer found six weeks after exposure. It is concluded that rabbits exposed to paraquat aerosol develop a severe pneumonitis that resolves if exposure is stopped and recovery time is allowed; physiological abnormalities remain, however.