Betamethasone effects on paraquat lung toxicity.

1. Betamethasone (1 mg/ml) was administered i.v. to adult Wistar rats 3 h before paraquat injection (30 mg/ml) and various parameters of lung function were studied to determine the effect of an anti-inflammatory drug in paraquat lung toxicity. 2. Rats treated with both drugs showed not only increases in spontaneous lung chemiluminescence (90%), malondialdehyde formation (40%), migration of PMN cells to the lungs (450%) and lung wet wt (20%), but also the survival times were decreased to 25% at day 7. 3. The data indicate that betamethasone exacerbates the toxic effects of paraquat. The mechanism can be explained in terms of inhibition of phospholipase A2 activity, which may increase the accumulation of hydroperoxide, produced by paraquat redox cycling upon lipid membranes.