Oxygen-derived
free radicals are known to take part in cardiac injury during post-ischemic reperfusion (I/R).
Xanthine oxidase (XO) is closely associated with the generation of
superoxide radicals. We have determined the distribution of XO in rat myocardium after
ischemia (I) and I/R by immunocytochemical method using murine
monoclonal antibody against XO (bovine milk) and by
enzyme histochemistry (EHC) in situ. Frozen sections of
periodate-lysine-paraformaldehyde (PLP) fixed myocardium after 15, 60 and 90 min
ischemia and 15 min
ischemia and 30 min reperfusion were processed for immunocytochemistry and EHC. In other experiments, rats were treated with
allopurinol, an inhibitor of XO, and hearts were processed for immunocytochemistry. By immunoperoxidase and immunofluorescence methods, a deep staining of interstitial cells, capillary and small blood vessels was observed, but the staining intensity of these cells was increased after reperfusion, in comparison to the normal and ischemic heart tissue. In the electron microscope, an immunoperoxidase reaction product was seen in the cytoplasm of interstitial, endothelial and smooth muscle cells. Similarly, EHC studies by
nitroblue tetrazolium staining showed an increase in enzymatic activity in the tissue after reperfusion. The
allopurinol-treated I/R tissue exhibited reduced staining. The data suggest that XO activity increases during
ischemia but intensifies after reperfusion. The
enzyme is localized in interstitial cells, coronary vessel endothelium and smooth muscle cells. XO is constantly present in the interstitial cells of the myocardium and it is a new finding not previously reported. It is further suggested that myocardial interstitium may be one of the major sites where
oxygen derived radicals are generated during
ischemia.