Cytochemical evidence of NADH-oxidase activity in the isolated working rabbit heart subjected to normothermic global ischaemia

Summary The cytochemical localization of NADH-oxidase, a possible source of oxygen derived toxic species was studied in the isolated working rabbit heart subjected to normothermic global ischaemia. The activity of this oxidase could be important for the damage observed during ischaemia, when cellular defence mechanisms against free radicals are depleted. In non-ischaemic myocardium only small amounts of the NADH-oxidase reaction product were present in the mitochondria. Although the reaction product could already be observed after 45 min of incubation, prolonged incubation times up to 2 h were necessary to clearly define these reactive sites. The reaction product is substrate dependent and is not affected by cyanide. Exposure of the hearts to ischaemia resulted in an alteration of the enzyme activity depending on the degree of ischaemic damage. In ultrastructurally slightly altered areas a high degree of cytochemical study supports the hypothesis that hydrogen peroxide and oxygen radicals produced in the mitochondria by NADH-oxidase activity may contribute to the mitochondrial damage observed during ischaemia when NADH is no longer oxidized by the respiratory chain and cellular defence mechanisms are impaired.