The influence of hypoxic cell-free perfusion and ischemia on cell morphology in the proximal tubular S2-segment of the rat kidney

Ameliorative effect of adenosine on hypoxia-reoxygenation injury in LLC-PK1, a porcine kidney cell line

We studied the effects of adenosine on injury caused by hypoxia and reoxygenation in LLC-PK1 cells. Lactate dehydrogenase and gamma-glutamyltranspeptidase were released from cells exposed to hypoxia for 6 hr and then reoxygenation for 1 hr. The addition of adenosine at 100 microM to the medium before hypoxia began significantly decreased enzyme leakage into medium during both hypoxia and reoxygenation. The adenosine A1-receptor agonist, R(-)-N6-(2-phenylisopropyl)adenosine (R-PIA), at the concentration of 100 microM, did not affect enzyme release, but the adenosine A2-receptor agonist 2-p-[2-car-boxyethyl]phenethyl-amino-5'-N-ethylcarboxamido-adenosi ne hydrochloride (CGS 21680) at the concentration of 100 nM, suppressed the injury caused by hypoxia and reoxygenation. There were decreases in cAMP contents and ATP levels in LLC-PK1 cells injured by hypoxia and reoxygenation. Adenosine (100 microM) restored ATP levels in the cells during reoxygenation. With adenosine, the intracellular cAMP level was increased prominently during reoxygenation. These results suggest that adenosine protects LLC-PK1 cells from injury caused by hypoxia and reoxygenation by increasing the intracellular cAMP level via adenosine A2 receptor.

Ischemia-reperfusion injury of rat kidney relates more to tubular than to microcirculatory disturbances

Several pathophysiological mechanisms have been purported to be involved in the development of acute ischemic renal failure, such as impairment of tubular function and/or of the renal microcirculation. However, it has not been elucidated as yet which of these mechanisms relates to the extent of kidney damage. Besides, little is known about the time course relationship between tubular and microcirculatory disturbances during the development of ischemia-reperfusion injury. We therefore performed intravital videomicroscopy of the proximal tubules as well as the peritubular microcirculation of the rat renal cortex during the first 24 hr of reperfusion after varying lengths of warm ischemia (30 min, 30 WI group; 60 min, 60 WI group; 90 min, 90 WI group). In a separate group of animals subjected to the same protocol, the survival rate (SR) was determined. The SR in these groups were 100%, 20% and 0%, respectively. Initially, the tubular and microcirculatory changes (i.e., increased tubular diameter and reduced capillary blood flow) relate well to the length of warm ischemia as well as the SR. At a later stage of reperfusion, however, we observed that peritubular capillary blood flow and tubular diameter recovered more quickly in the 90 WI group than in the 30 WI and 60 WI groups. As a result, these parameters as obtained at 24 hr of reperfusion did not relate anymore to the survival rate. Besides, at this stage a severe loss of integrity of the tubular wall was noted in the 60 WI and 90 WI groups. These findings suggest that kidney viability is not determined by the extent of recovery of microcirculatory blood flow and/or tubular diameter during early reperfusion, but by the integrity of the tubular wall.

Hypoxia and reoxygenation-induced injury of renal epithelial cells: effect of free radical scavengers

The aim of this study was to characterize injuries of LLC-PK1 and MDCK cells exposed to hypoxia and reoxygenation. Exposure of LLC-PK1 cells to hypoxia reduced the ATP contents and increased the leakage of lactate dehydrogenase (LDH), but MDCK cells had no such injuries. Hypoxia-reoxygenation of LLC-PK1 cells dramatically increased LDH leakage, which was suppressed by free radical scavengers, N,N'-diphenyl-p-phenylenediamine, superoxide dismutase and N,N'-dimethylthiourea. These results suggest that use of LLC-PK1 cells has advantages for the investigation of ischemia-reperfusion injury of the kidney as an in vitro model and that generation of oxygen radicals is involved in the cellular injury induced by hypoxia-reoxygenation.