Pressure natriuresis and renal medullary blood flow in dogs
Majid, D.S.; Godfrey, M.; Navar, L.G.
Hypertension 29(4): 1051-1057
1997
ISSN/ISBN: 0194-911X PMID: 9095098 Document Number: 480749
In the present study, we evaluated the effects of changes in arterial pressure on regional renal blood flows and sodium excretion in anesthetized dogs during control conditions and after 5% volume expansion with isotonic saline. Medullary and cortical blood flow responses were determined with laser-Doppler needle flow probes inserted into the midmedullary and midcortical regions, and whole-kidney blood flow was assessed with an electromagnetic flow probe. Volume expansion in six dogs caused marked increases in urine flow (20.2 +- 5.5 to 82.5 +- 22.7 mu-L cntdot min-1 cntdot g-1) and sodium excretion (3.2 +- 0.5 to 11.1 +- 2.7 mu-mol cntdot min-1 cntdot g-1), with slight increases in glomerular filtration rate (0.92 +- 0.03 to 1.01 +- 0.02 mL cntdot min-1 cntdot g-1) but no significant changes in total renal blood flow (4.7 +- 0.3 to 5.2 +- 0.6 mL cntdot min-1 cntdot g-1), medullary blood flow (+6 +- 9%), or cortical blood flow (+12 +- 10%). During stepwise reductions in renal arterial pressure (150 to 75 mm Hg) elicited with a renal arterial occluder, both before and after volume expansion, medullary, cortical, and total renal blood flows as well as glomerular filtration rate exhibited efficient autoregulation, with slopes not significantly different from zero over this range of arterial pressure. There were marked increases in the slopes of the relationships between arterial pressure and urine flow (0.18-0.05 to 0.78 +- 0.27 mu-L cntdot min-1 cntdot g-1 cntdot mm Hg-1) as well as sodium excretion (0.03 +- 0.004 to 0.10 +- 0.03 mu-mol cntdot min-1 cntdot g-1 cntdot mm Hg-1) during volume expansion. These data demonstrate that medullary blood flow is efficiently autoregulated in dogs during control and volume-expanded states and indicate that the mechanism responsible for the arterial pressure-induced changes in sodium excretion does not depend on coincident alterations in medullary blood flow.