Xanthine oxidase is increased and contributes to paraquat-induced acute lung injury. 
Two lines of investigation suggested that xanthine oxidase- (XO) derived O2 metabolites contribute to paraquat- (PQ) induced acute lung injury.  First, PQ treatment increased lung XO activity and decreased lung xanthine dehydrogenase activity.  Second, lung albumin uptake increased compared with control values in untreated XO-replete but not tungsten-treated XO-depleted lungs in rats treated with PQ.