Changes in Renal Interstitial Fluid Pressure Do Not Mediate Arterial Pressure‐induced Medullary NO Production

Abstract

The present study examined whether renal outer medullary NO production, as reflected by changes in NO3+NO2, would be enhanced by increased renal perfusion pressure (RPP) and whether this is related to associated changes of renal interstitial fluid pressure (RIFP). Two groups of male Sprague Dawley rats (10 wks) were compared; intact renal capsule (IN; n=7) and decapsulated (DC; n=6). The left kidney was denervated, a linear microdialysis probe implanted into the outer medulla, and urine collected from a catheter in the left ureter. Medullary interstitial and urinary excretion of NO3+NO2 were determined. An adjustable aortic occluder proximal and distal to the left renal artery was used to increase RPP from 80 to 110 to 140 mmHg. As RPP increased, medullary NO3+NO2 increased significantly in both groups (IN= 9.2+2.8, 13.8+3.9 to 16.1+3.9; DC= 8.9+2.4, 15.7+3.2 to 16.9+3.3 uM) as did urinary NO3+NO2 excretion (IN= 1.6+0.9, 7.0+2.9 to 11.1+4.8; DC= 1.1+0.3, 6.6+0.9 to 7.8+1.3 nmol/min/g kwt). Only natriuresis and diuresis were significantly blunted in the DC group. We conclude that acute increases in RPP within the autoregulatory range induces a concomitant increase in intrarenal NO production independent of the RIFP‐determined pressure‐natriuresis component and may be a consequence of increases of medullary blood flow.