MODULATION OF HYDROGEN-PEROXIDE RELEASE FROM VASCULAR ENDOTHELIAL-CELLS BY OXYGEN

We have investigated factors that regulate hydrogen peroxide (H2O2) re lease from vascular endothelial cells. Endothelial cells produce H2O2 at an intracellular site in the vicinity of peroxisomes and at a secon d site near the cell surface that is inaccessible to intracellular cat alase or glutathione peroxidase. Regulation of H2O2 generation at the intracellular site was studied using aminotriazole, which inactivates catalase in the presence of H2O2. Regulation of H2O2 generation at the second site was studied by measuring H2O2 release into the medium. Th e rate of H2O2 release was constant over 2 h when cells were incubated in room air. Changing O-2 levels in the atmosphere from O% to 10% O-2 resulted in a threefold increase in the rate of H2O2 release. Elevati on of O-2 levels from 10% to 95% O-2 produced no further enhancement i n the rate of release. Preincubation of cells under hypoxic conditions did not lead to an exaggerated rate of H2O2 release when cells were r eturned to room air. Pretreatment of cells with exogenous H2O2 inhibit ed subsequent H2O2 release while pretreatment with catalase enhanced H 2O2 release. Although arachidonic acid transiently enhanced the rate o f H2O2 release through a mechanism dependent on PGH synthase, basal H2 O2 release was independent of this enzyme. Neither hypoxia, hyperoxia, or hypoxia followed by reoxygenation altered H2O2 generation at the i ntracellular site accessible to peroxisomal catalase. These data demon strate that H2O2 release from endothelial cells is responsive to chang es in O-2 concentrations over a narrow range. The mechanisms involved are subject to product inhibition and appear to be saturated at 10% O- 2 in the atmosphere.