Free radicals appear to play a major role in the reperfusion injury of the myocardium. Iron chelators and antioxidants can prevent the reperfusion injury. The cellular source of free radicals during reperfusion is not clearly established. However, an important source may be the endothelial cells (EC). The protective effect of iron chelators and antioxidants on reperfusion injury of the myocardium may be partially mediated by their effect on vascular EC, which may attenuate the formation of hydroxyl radicals. We examined the protective effect of deferoxamine and antioxidants on iron-dependent free radical-mediated damage to EC and membrane lipid peroxidation and compared it with those of a new class of compounds (21-aminosteroids: U-74389F, U-74500A, U-78517F) which have both antioxidant and iron chelating properties. We examined viability of the EC and membrane lipid peroxidation using primary aortic EC. First, the effect of increasing iron concentration (0-3.8 microM) (added as ferric ammonium citrate) was characterized. We then examined the effect of deferoxamine (1-10 microM), butylated hydroxytoluene (BHT 1-10 mM), probucol (0.5-5.0 mM), allopurinol (1-1,000 microM), U-74389F (2-20 microM), U-74500A (1-5 microM), and U-78517F (0.1-1.0 microM) on reversing the effect of iron. With increasing iron concentration, there was a significant decrease in the viability of dog aortic or bovine pulmonary arterial EC as compared with NIH 3T3 or human fibroblasts. Equally, there was also a significant increase in lipid peroxidation of the cellular membranes. There were significant differences between the compounds with respect to their ability to maintain the viability of EC and prevent membrane lipid peroxidation.(ABSTRACT TRUNCATED AT 250 WORDS)