ROLE OF PRESSURE NATRIURESIS IN LONG-TERM CONTROL OF RENAL ELECTROLYTE EXCRETION

If pressure natriuresis is to play an important role in arterial press ure 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 hem odynamics and electrolyte excretion chronically. Female mongrel dogs ( n=6) were instrumented with bilateral renal artery catheters for measu rement of renal perfusion pressure and occluders on both renal arterie s for servo-control of renal perfusion pressure at different levels; t he urinary bladder was split for determination of renal clearances and electrolyte excretion from each kidney separately. Because both kidne ys were exposed to the same neurohumoral influences, any changes in re nal function could be attributed to differences in renal perfusion pre ssure between the two kidneys. After 5 days of control, renal perfusio n 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 mmo l/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. U rine volume, chloride excretion, and potassium excretion exhibited sim ilar patterns during servo-control. In addition, autoregulation of eff ective renal plasma flow and glomerular filtration rate was relatively well maintained; however, in the low-pressure kidney, glomerular filt ration rate was slightly but significantly lower (approximately 8%) th an 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 i mportant long-term controller of sodium and water excretion.