ABSTRACT. Reactive osygen metabolites have an important role in ischemia-reperfusion injury. One of the sources of reactive osygen metabolites is santhine osidase, which is present in several tissues but is also released into the circulation after ischemia. We studied the effect of several potentially protective compounds on adenine nucleotide depletion induced by extracellular santhine osidase and hypoxanthine, in concentrations relevant to human pathophysiology. In umbilical vein endothelial cells prelabeled with '"C-adenine, cellular adenine nucleotides retained 64 f 9% of the initial radioactivity over a 4-11 incubation with culture medium (controls), whereas in the presence of xanthine osidase (80 mU/mL) and hyposanthine (100 phl), only 3 2 4% of radioactivity remained in cellular nucleotides, the rest appearing in catabolic products in the medium. Glutathione and 3-aminobenzamide, an inhibitor of poly-ADP-ribose polymerase, partly prevented the nucleotide depletion (adenine nucleotide radioactivity 15 f 6% to 3 3 f 13% of total), but scavengers of the Ilydrosyl radical, dimethylthiourea and DhISO, a s rvell a s vitamins E and C, were without effect. Superoside dismutase prevented the leakage of nucleotides into the culture medium but not intracellular nucleotide catabolism, whereas the latter process was decreased by catalase, consistent with predominant effects of superoside and hydrogen peroxide at the cell membrane and interior, respectively. (Pediatr Res 34: 572-576, 1993)