AIM: To investigate experimentally ultrastructural and biochemical signs of acute injury to the renal parenchyma after warm renal ischemia of various duration and subsequent reperfusion.

MATERIALS AND METHODS: The experiments were performed on 44 healthy conventional female rabbits of the "Chinchilla" breed weighted 2.6-2.7 kg, which were divided into four groups. In the first, control, group included pseudo-operated animals. In the remaining three groups, an experimental model of warm ischemia of renal tissue was created, followed by a 60-minute reperfusion. The renal warm ischemia time was 30, 60 and 90 minutes in the 2nd, 3rd and 4th groups, respectively. Electron microscopy was used to study ultrastructural disturbances of the renal parenchyma. Biochemical signs of acute kidney damage were detected by measuring the following blood serum and/or urine analytes: NGAL, cystatin C, KIM-1, L-FABP, interleukin-18. The glomerular filtration was evaluated by creatinine clearance, which was determined on days 1, 5, 7, 14, 21 and 35 of follow-up.

RESULTS: A 30-minute renal warm ischemia followed by a 60-minute reperfusion induced swelling and edema of the brush membrane, vacuolation of the cytoplasm of the endothelial cells of the proximal tubules, and microvilli restructuring. The observed disorders were reversible, and the epithelial cells retained their viability. After 60 minutes of ischemia and 60 minutes of reperfusion, the observed changes in the ultrastructure of the epithelial cells were much more pronounced, some of the epithelial cells were in a state of apoptosis. 90 min of ischemia and 60 min of reperfusion resulted in electron-microscopic signs of the mass cellular death of the tubular epithelium. Concentration in serum and/or biochemical urine markers of acute renal damage increased sharply after ischemic-reperfusion injury. Restoration of indicators was observed only in cases when the renal warm ischemia time did not exceed 60 minutes. The decrease in creatinine clearance occurred in the first 24 hours after the intervention, lasting not less than two weeks after a 30-minute warm ischemia, at least 3 weeks after a 60-minute warm ischemia and continued more than a month after a 90-minute renal artery occlusion.

CONCLUSION: Intraoperative warm ischemia and subsequent reperfusion are the actual reasons for the alteration of the ultrastructure of the renal tissue and the impairment of the filtration function. The severity of the disorders depends on the duration of the damaging factors. After a 30-60-minute ischemia, the structural and functional changes in the renal tissue are reversible. The mass death of nephrocytes-effectors is possible only after warm renal ischemia longer than 60 min.