['In order to determine the mechanism of the protective effect of a urinary trypsin inhibitor (UTI) on renal ischemic reperfusion injury, we measured the tissue oxygen partial pressure pO2 in both the renal cortex and medulla in rats, using electron paramagnetic resonance (EPR) oximetry.', 'We allocated the rats to three groups: normal saline (NS) group, a UTI 50,000 U x kg(-1) (LD) group, and a UTI 150,000 U x kg(-1) (HD) group, with the normal saline and UTI being administered 30 min before ischemia. Renal ischemia was achieved by inflating the balloon of a vascular occluder that had been placed around the abdominal aorta just above the bifurcation of the renal artery. Cortical and medullary pO2 were measured every 10 min during ischemia (30 min) and reperfusion (60 min) by EPR oximetry; also, systemic cardiopulmonary parameters were measured.', 'The pO2 in the cortex and medulla decreased to less than 2 mmHg during ischemia in all groups. At 60 min after reperfusion, the pO2 values in the NS group were not fully restored, whereas those in the LD and HD groups were completely restored to the pre-ischemic values. There were no significant differences between the HD and LD groups. There were no differences between any groups in cardiopulmonary parameters.'] Does urinary trypsin inhibitor ameliorate renal tissue oxygenation after ischemic reperfusion in rats?