An isolated perfused rat kidney preparation designed for assessment of glomerular permeability characteristics

The aim of the present investigation was to modify the widely used isolated perfused rat kidney preparation to make it more suitable for studies of glomerular permeability to macromolecules. Both kidneys were perfused in situ using separate pumps in two of each other independent systems with Tyrode-solution containing human serum albumin (18.2 g l-1). Sodium nitroprusside was administered to induce dilatation and to maintain constant vascular resistance (PRU100) during the experiments. The addition of sodium nitroprusside decreased vascular resistance from 0.17 +/- 0.05 to 0.09 +/- 0.02 mmHg min-1 100 g-1 ml-1 and increased urine flow and glomerular filtration rate. The temperature of the perfusate was reduced from 37 degrees C to 8 degrees C to inhibit tubular reabsorption of protein and fluid, resulting in a urine to plasma concentration ratio of [51Cr]EDTA of 1.26 +/- 0.07. Furosemide reduced the urine to plasma concentration ratio for [51Cr]EDTA further to 1.15 +/- 0.02 and increased glomerular filtration rate. Moreover, by performing the studies at low temperatures (8 degrees C) in the presence of sodium nitroprusside and furosemide it was possible to achieve low and stable albumin fractional clearance values close to those prevailing in vivo. Thus, the described technique, allowing simultaneous perfusions of both kidneys with different solutions, pressures and flows, seem to be well suited for studies of macromolecular transport across glomerular capillaries.