Ultrapure polymerized bovine hemoglobin (UPPBHb) improves integrity of the isolated perfused rat kidney (IPRK): effects on function and structure.

To test the oxyphoretic properties and potential nephrotoxic side-effects of polymerized hemoglobin solutions, isolated rat kidneys were perfused in a recirculating system for 180 min. Group I was perfused with a substrate enriched Ringer solution containing hydroxyethylstarch (HES) to produce isoncotic conditions. In group II HES was substituted in part by UPPBHb (34 g/l) with a high portion of low molecular weight molecules (= UPPBHb1). In group III 34 g/l of UPPBHb containing an increased fraction of high molecular weight polymers (= UPPBHb2) was used. Only UPPBHb2-perfused kidneys showed a reduced renal perfusate flow (RPF, 13.3 ± 1.1 ml/min g kw), when compared to HES-perfused controls (15.5 ± 0.8) and UPPBHb1 (15.1 ± 1.2). Glomerular filtration rate (GFR) was significantly higher in UPPBHb1-perfused kidneys (902 ± 107 vs 633 ± 55 μl/min g kw for HES). This difference became even more pronounced in the third hour of perfusion (474 ± 125 vs. 103 ± 33). In contrast, UPPBHb2 produced low initial GFR levels of 385 ± 25, which had only a minor tendency to decline with time. Parallel to GFR, absolute reabsorption of sodium (T Na ) andoxygen consumption (Q O2 ) showed values of 110 ± 16 and 5.46 ± 0.33 μmol/min g kw in UPPBHb1-kidneys vs 83 ± 6 and 5.09 ± 0.27 in controls and vs 53 ± 4 and 3.66 ± 0.12 in UPPBHb2-kidneys. Fractional excretion of sodium (FE Na ), of potassium (FE K ), and of water (FE H2o ) in UPPBHb1 and UPPBHb2-perfused kidneys were not significantly different from HES-perfused controls at any time of perfusion. Urinary flow rate (UFR) was similar in UPPBHbl- and HES-kidneys. Nevertheless, control kidneys tended to render oliguric during the third hour of perfusion (UFR 19.9 ± 4.1 μl/min g kw), whereas UPPBHb1 preserved urinary flow in a better way (83.7 ± 32.4). UFR of UPPBHb2-kidneys was significantly reduced initially (30.2 ± 5.1 vs. 105 ± 33 for HES), but increased steadily up to 67 ± 23. In the UPPBHb1 and HES group, all functional parameters determined declined dramatically within the third hour of perfusion, whereas UPPBHb2 produced functional stability. The in vivo reaction pattern of renal autoregulation was better preserved in UPPBHb-perfused kidneys than in HES-perfused controls : 74 ± 6 vs. 59 ± 5 vs. 42 ± 4% (of full autoregulatory response) for UPPBHb1, UPPBHb2, and HES kidneys, respectively. Light- and electron microscopic analysis revealed major alterations only for the outer medulla of HES-kidneys. Especially in the inner stripe of the outer medulla (ISOM), which is the zone of greatest sensitivity to damage in the isolated perfused kidney, severe hydropic degeneration, cell detachment and necrotic destruction of the medullary thick ascending limb (mTAL) was confined to the HES-perfused group, whereas in the UPPBHb1 group mTAL was well preserved. The results suggest that UPPBHb2, although stabilizing the IPRK during prolonged perfusion periods, was not as effective as UPPBHb1 for preserving kidney function in the IPRK-system. UPPBHb1 provided better oxygenation than HES perfusion and did not exert detectable nephrotoxic effects on the IPRK.