Purine nucleoside phosphorylase: a new marker for free oxygen radical injury to the endothelial cell.

The effect of ischemia and reperfusion on purine nucleoside phosphorylase was studied in an isolated perfused rat liver model. This enzyme is localized primarily in the cytoplasm of the endothelial and Kupffer cells; some activity is associated with the parenchymal cells. Levels of this enzyme accurately predicted the extent of ischemia and reperfusion damage to the microvascular endothelial cell of the liver. Livers from Lewis rats were subjected to 30, 45 and 60 min of warm (37 degrees C) no flow ischemia that was followed by a standard reperfusion period lasting 45 min. Purine nucleoside phosphorylase was measured at the end of the no flow ischemia and reperfusion periods as was superoxide generation (O2-). Bile production was monitored throughout the no flow ischemia and reperfusion periods. Control perfusions were carried out for 120 min. A significant rise in purine nucleoside phosphorylase levels as compared with controls was observed at the end of ischemia in all the three groups. The highest level, 203.5 +/- 29.2 mU/ml, was observed after 60 min of ischemia. After the reperfusion period, levels of purine nucleoside phosphorylase decreased in the 30- and 45-min groups 58.17 +/- 9.66 mU/ml and 67.5 +/- 17.1 mU/ml, respectively. These levels were equal to control perfusions. In contrast, after 60 min of ischemia, levels of purine nucleoside phosphorylase decreased early in the reperfusion period and then rose to 127.8 +/- 14.8 mU/ml by the end of reperfusion (p less than 0.0001). Superoxide generation at the beginning of reperfusion was higher than in controls with similar values observed at the end of 30, 45 and 60 min of ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)