The influence of selected -receptor blockers on iron overload and oxidative stress in endothelial cells (ECs) was assessed. Confluent bovine ECs were loaded with iron dextran (15 M) for 24 h and then exposed to dihydroxyfumarate (DHF), a source of reactive oxygen species, for up to 2 h. Intracellular oxidant formation, monitored by fluorescence of 2Ј,7Ј-dichlorofluorescin (DCF; 30 M), increased and peaked at 30 min; total glutathione decreased by 52 Ϯ 5% (p Ͻ 0.01) at 60 min. When the ECs were pretreated 30 min before iron loading with 1.25 to 10 M D-propranolol, glutathione losses were attenuated 15 to 80%, with EC 50 ϭ 3.1 M. D-Propranolol partially inhibited the DCF intensity increase, but atenolol up to 10 M was ineffective. At 2 h, caspase 3 activity was elevated 3.2 Ϯ 0.3-fold (p Ͻ 0.01) in the iron-loaded and DHF-treated ECs, and cell survival, determined 24 h later, decreased 47 Ϯ 6% (p Ͻ 0.01). Ten micromoles of D-propranolol suppressed the caspase 3 activation by 63% (p Ͻ 0.05) and preserved cell survival back to 88% of control (p Ͻ 0.01). In separate experiments, 24-h iron loading resulted in a 3.6 Ϯ 0.8-fold increase in total EC iron determined by atomic absorption spectroscopy; D-propranolol at 5 M reduced this increase to 1.5 Ϯ 0.4-fold (p Ͻ 0.01) of controls. Microscopic observation by Perls' staining revealed that the excessive iron accumulated in vesicular endosomal/lysosomal structures, which were substantially diminished by D-propranolol. We previously showed that propranolol could readily concentrate into the lysosomes and raise the intralysosomal pH; it is suggested that the lysosomotropic properties of D-propranolol retarded the EC iron accumulation and thereby conferred the protective effects against iron load-mediated cytotoxicity.