In this study, the responses to H2O2 are in agreement with
earlier reports.5 The expression of eNOS in endothelial cells
is regulated by NO through a negative feedback mechanism
at both the transcriptional and translational levels. Hydrogen
peroxide-derived upregulation of eNOS was mediated by
diminished NO availability and a consequent reduction in
the negative feedback regulatory action of NO on eNOS
expression. This represents a compensatory protective
mechanism of the cells to a reduction in NO availability
induced by acute exposure to H2O2.5 Hydrogen peroxide has
been shown to increase eNOS activity by inducing changes
in the phosphorylation status of the enzyme. This response
represents an attempt by the endothelial cells to maintain NO
bioactivity under conditions of increased oxidative stress