Bovine aortic endothelial cells release hydrogen peroxide

Endothelial cells grown on microcarriers are able to release H 2 O 2 to the extracellular environment without any added stimulus. The extracellularly released H 2 O 2 can be detected by luminol‐amplified chemiluminescence (CL) if horseradish peroxidase is added. The CL response can be reduced by catalase and blocked by superoxide dismutase, indicating that O 2 ‐could be a precursor for H 2 O 2 . The CL kinetics, i.e., a long lag time followed by a rapid shift to a new level, indicate activation of an O 2 ‐producing enzyme. The cells are also able to protect themselves from H 2 O 2 stimulation by both catalase and the glutatione system. Bradykinin stimulates the H 2 O 2 release, but if the effect is directly stimulatory or if it acts by reduction of the protective system is at present unclear. The extracellularly released H 2 O 2 could be a cause of injury to the endothelial cells or to the subendothelial matrix.