Mannitol Reduces the Hydrostatic Pressure in the Proximal Tubule of the Isolated Blood-Perfused Rabbit Kidney during Hypoxic Stress and Improves Its Function.

Background/aims: Hypoxia may play a role in the development of renal failure in donated kidneys. In the present study, the effects of hypoxia on isolated blood-perfused rabbit kidneys were investigated and the effects of mannitol were explored, giving special attention to intratubular pressure.

Methods: Kidneys were perfused with their autologous blood during four 30-min periods (P1-P4). P1 was considered baseline function. In P2, hypoxia was induced either alone or with an infusion of mannitol (15 mg/min) during P2-P4. Reoxygenation was applied after P2. Proximal intratubular pressure was measured in all conditions.

Results: During hypoxia, renal blood flow doubled and restored immediately in P3. Urine flow stopped in P2, except in the series with mannitol, but gradually resumed in P3 and P4. Likewise, creatinine clearance recovered slightly (<25%) in P4, except for the series with mannitol, where it still could be measured in P2 and reached a value >50% of P1. Proximal intratubular pressure (mean ± SD) increased from 12 ± 5 in P1 to 24 ± 11 mm Hg during hypoxia and returned to 10 ± 6 mm Hg in P3. This increase was not observed with mannitol.

Conclusion: Cellular swelling might be responsible for the suppressed filtration during hypoxia and can be prevented by mannitol.