Steroid Pretreatment Does Not Prevent Paraquat Pneumonitis in Rabbits

Rabbits exposed to paraquat develop interstitial pneumonitis. A sublethal dose of paraquat (PQ) solution (250mg/100ml) 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, methylpred-nisolone (MP) treated (1mg/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 −0.35kg) 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]. Bron-choalveolar 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 100ml lavage were comparable in all groups (approximately 3×107 cells). Steroid did not prevent the development of pathologic change.