HYDROGEN-PEROXIDE (H2O2) PRODUCTION BY MONOAMINE-OXIDASE IN RAT-TISSUES USING ENDOGENOUS CATECHOLAMINES AS SUBSTRATES - A COMPARISON OF CATALYTIC MONOAMINE-OXIDASE HISTOCHEMISTRY AND RECENTLY PUBLISHED CATECHOL-O-METHYLTRANSFERASE IMMUNOHISTOCHEMISTRY

Histochemical studies on hydrogen peroxide (H2O2) production by monoam ine oxidase (MAOX) using xenobiotic (foreign) catecholamines such as t ryptamine or tyramine as substrates may not reveal the true H2O2-produ ction capacity of this enzyme and the potential co-localization and co operation of MAOX with catechol-O-methyltransferase (COMT), the other catecholamine-degrading enzyme. Therefore, in the present study the ca techolamine hormones adrenaline (epinephrine) and noradrenaline (norep inephrine) and the catecholamine neurotransmitter noradrenaline as wel l as the COMT metabolites metanephrine and normetanephrine, which ace likely to be the more important MAOX substrates, were used for MAOX vi sualization in many rat tissues with a cerium-diaminobenzidine-H2O2-Co method. Adrenaline and noradrenaline were autooxidized by Ce3+ and co uld not be employed; with metanephrine or normetanephrine as substrate s MAOX produced considerable amounts of H2O2 in many cells and tissues . Comparisons with immunohistochemical COMT-data for rats from the lit erature show that MAOX and COMT are co-localized or not. Therefore, di fferent from our current knowledge in rats COMT and MAOX either co-ope rate in catecholamine degradation or they degrade the respective catec holamines alone.