First 11 pages of thesis. - OPUS - Universität Würzburg

oxide’s metabolite nitrite, ESR directly detects nitric oxide as a specific hyperfine
triplet peak 190 . Our experiments show a significant reduction of baseline nitric
oxide formation in the vessel wall of apoE/eNOS dko, compared to apoE ko
mice. In addition, the in vivo concentration of circulating nitrosyl hemoglobin, a
measure for nitric oxide bioavailability in the circulation, was markedly reduced
in apoE/eNOS dko mice. Our data suggest that eNOS is the major contributor of
vascular and circulating nitric oxide despite all these possibilities. Since eNOS
is expressed in the endothelium lining the lumen of the vessel, the nitric oxide
generated by eNOS can easily diffuse into the circulation, explaining the
significant contribution of eNOS to circulating levels of nitric oxide.
To assess vascular superoxide formation we used a HPLC assay which
measures the formation of oxyethidium, a specific reaction product of
dihydroethidium with superoxide 199 . These measurements revealed a significant
reduction in superoxide production following genetic deletion of the enzyme
(chronic) in apoE/eNOS dko, and acute pharmacological inhibition of eNOS in
apoE ko. The reduction of superoxide generation observed in apoE/eNOS dko
reflects the specific contribution of eNOS derived superoxide production in
endothelial cells. Since both, significant nitric oxide and superoxide production
by eNOS is detectable in apoE ko mice, we conclude that eNOS is partially
uncoupled during atherosclerosis development in this model. We speculate that
eNOS produces nitric oxide in the healthy regions of the vessel, whereas in the
diseased regions, it is uncoupled and contributes to superoxide production.
As recently shown in eNOS transgenic apoE ko mice, reduced nitric
oxide and increased superoxide generation by uncoupled eNOS can accelerate
atherosclerosis 151 . However, despite decreased vascular superoxide formation
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