Steroid pretreatment does not prevent paraquat pneumonitis in rabbits

Rabbits exposed to paraquat develop interstitial pneumonitis. A sublethal dose of paraquat (PQ) solution (250 mg/100 ml) was aerosolized by ultrasonic nebulization for one hour to rabbits in a closed vented chamber on two occasions with a five-day interval between exposures. Groups studied included saline-exposed (N = 4); saline-exposed, methylprednisolone (MP) treated (1 mg/kg daily IM starting one day prior to the first exposure and then throughout the exposure period until sacrifice at day 8) (N = 4); PQ-exposed (N = 6); and PQ-exposed, MP treated (N = 6). Controls and MP controls gained weight and showed no abnormalities of respiratory rate. PQ and PQ-MP animals lost weight (average -0.35 kg) and had decreased breathing frequency (average decrease, 80-90 BPM). Blood gases showed minimal changes in all groups, although some individuals had hypoxemia and an increased alveolar-arterial oxygen pressure quotient [P (A-a) O2]. Bronchoalveolar lavage at sacrifice showed a marked increase in the percent of neutrophils in PQ and PQ-MP animals that correlated with pathology scores (R = 0.83). The P(A-a)O2 correlated with both the percent of neutrophils in lavage and the pathology score. Total cells recovered from a 100 ml lavage were comparable in all groups (approximately 3 X 10(7) cells). Steroid did not prevent the development of pathologic change.