Iron-catalyzed formation of hydroxyl radicals has been postulated to occur during reperfusion of ischemic tissues. To assess the role of iron-catalyzed oxidant production in ischemia/reperfusion (I/R) injury to skeletal muscle, we examined the effects of deferoxamine (an iron chelator) and apotransferrin (an iron-binding protein) on the increased vascular permeability produced by I/R in isolated, pump-perfused rat hindquarters. Solvent drag reflection coefficients (sigma) were measured in hindquarters subjected to 2 h of ischemia and 30 min of reperfusion with either no pretreatment, pretreatment with 50 mg/kg deferoxamine, 200 mg/kg apotransferrin, or iron-loaded deferoxamine (50 mg/kg). I/R alone was associated with an increase in vascular permeability as indicated by the significantly lower estimates of sigma obtained after I/R (0.68 +/- 0.03) compared with those obtained in nonischemic preparations (0.82 +/- 0.02). Pretreatment with deferoxamine or apotransferrin attenuated this permeability increase (sigma = 0.83 +/- 0.03 and 0.86 +/- 0.02, respectively), whereas pretreatment with iron-loaded deferoxamine afforded no protection (sigma = 0.71 +/- 0.02). These findings are consistent with the hypothesis that iron-catalyzed oxidant production is important in the genesis of microvascular injury following I/R. Since the enzyme xanthine oxidase has been implicated as a major source of oxidants generated during reperfusion, we also measured tissue levels of xanthine oxidase and xanthine dehydrogenase in muscle samples obtained from the same hindquarters in which we measured permeability changes.(ABSTRACT TRUNCATED AT 250 WORDS)