Cross-linked hemoglobin increases fractional reabsorption and GFR in hypoxic isolated perfused rat kidneys

We compared the ability of human red blood cells (RBC) and a cell-free oxygen carrier to maintain isolated perfused kidney function under moderately hypoxic conditions. Recirculating perfusate was gassed initially with 93% air-7% CO2, and, after 30 min, the gas was changed to 12 O2-7 CO2-81% N2. Oxygen content of the perfusate was increased with RBC (30 g/l Hbg) or highly purified human hemoglobin Ao (HbAo) polymerized with O-raffinose (o-R-poly-Hb, 30 g/l Hbg). For comparison, kidneys were perfused with 60 g/l of bovine serum albumin (BSA) alone. The effects of unmodified hemoglobin were examined by adding 5 g/l of nonpolymerized HbAo to the BSA perfusate after 20 min. The effect of increasing oxygen delivery without hemoglobin was examined by switching to 93% O2 after 20 min during some BSA perfusions (BSA-HiO2). Vascular resistance decreased progressively in o-R-poly-Hb- and BSA-HiO2-perfused kidneys but remained constant in other experiments. Nitro-L-arginine methyl ester (L-NAME) prevented vasodilati...