Relation between vasa recta blood flow and renal interstitial hydrostatic pressure during pressure natriuresis

Pressure natriuresis may be mediated through increases in inner medullary vasa recta blood flow (QVR). By means of acute renal decapsulation to prevent increases in renal interstitial hydrostatic pressure (RIHP), the effect of increases in QVR in the presence and absence of changes in RIHP in the natriuretic and diuretic responses to increases in renal perfusion pressure (RPP) was evaluated. Blood flow in descending (QDVR) and ascending (QAVR) vasa recta was determined in the exposed papilla by fluorescence videomicroscopy in anesthetized euvolemic Munich Wistar rats. In rats with intact renal capsules (n = 12), increases in RPP from 101 +/- 0.5 to 132 +/- 2.9 mm Hg caused significant increases in QDVR (from 4.7 +/- 0.9 to 5.5 +/- 0.9 nl/min, p < 0.001) and QAVR (from 2.8 +/- 0.2 to 3.5 +/- 0.2 nl/min, p < 0.001) in association with increases in RIHP (from 4.6 +/- 1.3 to 7.6 +/- 1.3 mm Hg, p < 0.001), urine flow (from 16.2 +/- 2.6 to 20.2 +/- 3.2 microliters.min-1 x g kidney wt-1, p < 0.01), and urinary sodium excretion (from 2.10 +/- 0.38 to 3.36 +/- 0.62 mu eq.min-1 x g kidney wt-1, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)