Recovery from paraquat pneumonitis

New Zealand white rabbits were evaluated for recovery from paraquat induced pneumonitis 6 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 2 paraquat exposures (separated by a 5 day interval). Morphometric and pathological measurements were made at death either 3 days or 42 days after the second exposure. The animals killed 3 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 3 days after 2 exposures were no longer found 6 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.