Effect of renal arterial pressure on the stop-flow sodium minimum

An increase in renal perfusion pressure in the rat and dog elevates the stop-flow distal sodium minimum concentration. The following studies were done to define the mechanism of this change. Dog kidneys were perfused at selected pressures during stop flow. The sodium minimum concentration changed 0.8 mEq Na/liter urine for each 10 mm Hg change in perfusion pressure. This was not modified by infusion of angiotension II. Ureteral pressure varied directly with perfusion pressure. The point of maximum PAH secretion showed proximal displacement with increased perfusion pressure. The entrance of postocclusive filtration markers into more distal samples increased with elevated perfusion pressure. It is concluded that the increase in distal sodium minimum concentration occurring with increased perfusion pressure is probably due to an increase in filtration, intratubular pressure, and tubular dilatation, causing stop-flow distal sodium minimum concentration to equilibrate at a higher level.