(Hypertension. 1997;29:210.)
© 1997 American Heart Association, Inc.
Arthur C. Corcoran Memorial Lecture |
Pressure Natriuresis and Autoregulation of Inner Medullary Blood Flow in Canine Kidney
From the Department of Physiology, Tulane University School of Medicine, New Orleans, La.
Correspondence to Dewan S.A. Majid, PhD, Department of Physiology, SL39, Tulane University School of Medicine, 1430 Tulane Ave, New Orleans, LA 70112. E-mail majid{at}mailhost.tcs.tulane.edu
We have evaluated the responses to changes in arterial pressure on regional blood flows in the renal medulla and sodium excretion simultaneously in denervated kidneys of six anesthetized sodium-replete dogs. Renal regional blood flow responses were determined using laser-Doppler needle flow probes and whole-kidney blood flow was assessed using an electromagnetic flow probe. The responses to stepwise reductions in renal arterial pressure (140 to 70 mm Hg) were examined first with a laser-Doppler needle probe inserted in the outer medulla and then repeated after advancing the same probe in the inner medulla. There were no differences in the control values of total renal blood flow (4.4±0.7 to 4.5±0.5 mL·min-1·g-1), glomerular filtration rate (0.89±0.7 to 0.94±0.9 mL·min-1·g-1), sodium excretion (3.6±0.6 to 3.4±0.5 µmol·min-1·g-1), and urinary excretion rate of nitric oxide metabolites (nitrate/nitrite, 1.6±0.2 to 1.5±0.2 nmol·min-1·g-1) at the start of both experimental periods. During changes in renal arterial pressure, inner medullary blood flow exhibited efficient autoregulation similar to that in outer medullary blood flow. Usual excretory responses to reductions in renal arterial pressure as well as autoregulation of cortical and whole-kidney blood flows and glomerular filtration rate were observed in these dogs. The slopes of the relationship between arterial pressure and sodium excretion (0.046±0.007 to 0.044±0.009 µmol·min-1·g-1·mm Hg-1) or nitrate/nitrite excretion (0.014±0.003 to 0.013±0.003 nmol·min-1·g-1·mm Hg-1) were similar in both experimental periods. These data indicate that blood flow to the inner medulla is efficiently autoregulated as in outer medulla and cortex of the kidney in anesthetized dogs and demonstrate further that the arterial pressure-induced natriuretic responses do not require associated changes in medullary blood flow.
Key Words: renal autoregulation • laser-Doppler flowmetry • sodium excretion
Abbreviations: CBF = cortical blood flow • EMF = electromagnetic flow • FENa = fractional excretion of sodium • GFR = glomerular filtration rate • LDF = laser-Doppler flow • MBF = medullary blood flow • NO = nitric oxide • NO2 = nitrite • NO3 = nitrate • PU = perfusion unit • RAP = renal arterial pressure • RBF = renal blood flow • RIHP = renal interstitial hydrostatic pressure • SAP = systemic arterial pressure • UKV = potassium excretion • UNaV = sodium excretion
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