ANALYSIS OF THE PRESSURE-FLOW CHARACTERISTICS OF ISOLATED-PERFUSED RAT KIDNEYS WITH INHIBITED TUBULAR REABSORPTION

The renal hemodynamics were studied in an isolated perfused rat kidney model modified for investigations of the glomerular permeability char acteristics. The tubular reabsorptive activity was inhibited by perfus ion at low temperature (8 degrees C) in the presence of furosemide and nitroprusside resulting in a dramatic increase in the filtered load o f fluid and solute reaching the tubules and hence in tubular pressure. The glomerular filtration rate (GFR), arterial pressure (P-A) and nee dle pressure (intrarenal tissue pressure, P-iR) were continuously reco rded and the glomerular hydrostatic pressure was estimated by an arter ial occlusion technique. The pre- to postglomerular resistance ratio w as calculated from the pressure vs. GFR relationships for two perfusat es having differing oncotic pressures (pi = 5.5 and pi = 20 mmHg), fro m which estimations of glomerular hydrostatic pressures (P-GC) were co ncomitantly made. Thus, increases in Delta pi could be exactly counter balanced by equally large increases in P-GC for any given GFR, the nee dle and Bowman's capsule pressures being dependent on GFR but not on p lasma colloid oncotic pressure. The experimental interventions resulte d in a pronounced elevation of P-iR as compared with in vivo condition s, while the P-GC values were in a normal range, resulting in reduced glomerular filtration pressures. Furthermore, the clearance of albumin varied with the oncotic pressure in agreement with the notion of hete roporosity.