Trypan blue uptake and lactate dehydrogenase release were measured as indices of irreversible cell damage in isolated, perfused rat livers during low-flow hypoxia. In livers from fasted rats perfused in the anterograde direction, trypan blue uptake took place beginning at about 45 min of hypoxia. Cells which took up trypan blue first were located in narrow bands at the border between anoxic pericentral areas and normoxic periportal regions of the liver lobule. After longer periods of hypoxia, trypan blue uptake progressed towards the central vein until after 120 min virtually all cells in the pericentral regions were stained. Under these conditions, cells in periportal regions were spared. In perfusions in the retrograde direction, cell death began in midzonal regions and spread towards the portal vein. Release of lactate dehydrogenase into the effluent paralleled trypan blue uptake, beginning at about 40 min of low-flow hypoxia and peaking at 80 min. In contrast to livers from fasted rats, trypan blue was not taken up, and lactate dehydrogenase was not released in livers from fed rats exposed to low-flow hypoxia for as long as 120 min. To test the hypothesis that xanthine oxidase-mediated oxygen-free radical formation was involved in cell injury at the border between anoxic and normoxic regions (anoxic edge), allopurinol, an inhibitor of xanthine oxidase, was studied. Allopurinol (0.2 to 5 mM) delayed the release of lactate dehydrogenase during low-flow hypoxia in a dose-dependent fashion (e.g., 5 mM allopurinol delayed hypoxia-induced lactate dehydrogenase release by about 30 min).(ABSTRACT TRUNCATED AT 250 WORDS)