First 11 pages of thesis. - OPUS - Universität Würzburg

The generation of other reactive oxygen intermediates, such as hydrogen
peroxide or hydroxyl radical can also cause oxidation of ferricytochrome C and
consequently result in the underestimation of superoxide production 187 .
Furthermore, because of its inability to penetrate cells it can be used only to
measure extra cellular superoxide. Chemiluminescent methods of superoxide
and nitric oxide detection in vascular tissues have been widely used because of
the ability of the method to measure intracellular radical production, the alleged
specificity of the reaction, the minimal cellular toxicity and the purported
increased sensitivity compared with chemical measurements. However, there is
uncertainity concerning the precise mechanism of enhanced luminescence-
dependent radical formation, particularly in a cell or tissue based experimental
system. Therefore, chemiluminescent techniques do not reflect actual cellular
radical production.
2.2.1.1 Electron spin resonance (ESR)
The most commonly used methods for evaluation of superoxide and nitric
production in biological systems are based on reduction of cytochrome C and
chemiluminescence, respectively. But these techniques have limitations for the
quantitation of superoxide and nitric oxide due to the fact that cytochrome c and
luminescent probes can readily react with other products from activated cells 188 .
The only analytical approach that permits a highly specific and sensitive direct
detection of free radicals is ESR, also termed electron paramagnetic resonance
spectroscopy.
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