Role of Pressure Natriuresis in Long-term Control of Renal Electrolyte Excretion

If pressure natriuresis is to play an important role in arterial pressure control, renal perfusion pressure must have a long-term effect on urinary sodium excretion. The aim of this study was to quantitate the importance of renal perfusion pressure per se in controlling renal hemodynamics and electrolyte excretion chronically. Female mongrel dogs (n=6) were instrumented with bilateral renal artery catheters for measurement of renal perfusion pressure and occluders on both renal arteries for servo-control of renal perfusion pressure at different levels; the urinary bladder was split for determination of renal clearances and electrolyte excretion from each kidney separately. Because both kidneys were exposed to the same neurohumoral influences, any changes in renal function could be attributed to differences in renal perfusion pressure between the two kidneys. After 5 days of control, renal perfusion pressure to one kidney was reduced from 86.7±0.2 to 74.2±0.6 mm Hg for 12 days, and pressure in the contralateral kidney increased to 91.5±0.4 mm Hg. Sodium excretion decreased from 41±2 to 25±1 mmol/d in the servo-controlled kidney and increased from 41±1 to 55±1 mmol/d in the contralateral kidney during 12 days of servo-control. Urine volume, chloride excretion, and potassium excretion exhibited similar patterns during servo-control. In addition, autoregulation of effective renal plasma flow and glomerular filtration rate was relatively well maintained; however, in the low-pressure kidney, glomerular filtration rate was slightly but significantly lower (∼8%) than in the contralateral kidney. In summary, long-term changes in renal perfusion pressure caused sustained alterations in renal electrolyte excretion. These results suggest that renal perfusion pressure is an important long-term controller of sodium and water excretion.