Review for "Altered renal medullary blood flow: a key factor or a parallel event in control of sodium excretion and blood pressure?"

The control of renal medullary perfusion and the impact of alterations in medullary blood flow on renal function have been topics of research interest for almost four decades. Many studies have examined the vascular architecture of the renal medulla, the factors that regulate renal medullary blood flow, and the influence of medullary perfusion on sodium and water excretion and arterial pressure. Despite these studies, there are still a number of important unanswered questions in regard to the control of medullary perfusion and the influence of medullary blood flow on renal excretory function and blood pressure. This review will first address the vascular architecture of the renal medulla and the potential mechanisms whereby medullary perfusion may be regulated. The known extrarenal and local systems that influence the medullary vasculature will then be summarized. Finally, this review will present an overview of the evidence supporting the concept that selective changes in medullary perfusion can have a potent influence on sodium and water excretion with a long-term influence on arterial blood pressure regulation.

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Role of renal medullary blood flow in the development of L-NAME hypertension in rats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1995.268.2.r317 ◽

1995 ◽

Vol 268 (2) ◽

pp. R317-R323 ◽

Cited By ~ 29

Author(s):

K. Nakanishi ◽

D. L. Mattson ◽

A. W. Cowley

Keyword(s):

Blood Pressure ◽

Blood Flow ◽

Flow Distribution ◽

Renal Medulla ◽

Sodium Balance ◽

Cortical Blood Flow ◽

Medullary Blood Flow ◽

Intrarenal Blood Flow ◽

Renal Medullary Blood Flow ◽

Renal Cortical Blood Flow

The effect of chronic intravenous infusion of the nitric oxide inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 8.6 mg.kg-1.day-1) on blood pressure, intrarenal blood flow distribution, and sodium and water balance was studied in conscious rats. On the 1st day of intravenous L-NAME infusion, renal medullary blood flow was reduced by 22%, renal cortical blood flow was unaltered, approximately 1 meq of sodium and 12 ml of water were retained, and blood pressure increased from 96 +/- 2 to 118 +/- 2 mmHg. Medullary blood flow was maintained at this decreased level, sodium continued to be retained, body weight continued to increase, and blood pressure remained elevated for the 5 days of L-NAME infusion. During the postcontrol period, blood flow in the renal medulla returned to levels not significantly different from control; the animals went into negative sodium balance and stopped gaining weight, and blood pressure returned to control. The present experiments indicate that decreased renal medullary blood flow and retention of sodium and water play an important role in the development of hypertension during chronic systemic L-NAME administration despite no measurable changes in renal cortical blood flow.

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Effect of atrial natriuretic peptide on vasa recta blood flow in the rat

AJP Renal Physiology ◽

10.1152/ajprenal.1987.252.6.f1112 ◽

1987 ◽

Vol 252 (6) ◽

pp. F1112-F1117 ◽

Cited By ~ 4

Author(s):

B. A. Kiberd ◽

T. S. Larson ◽

C. R. Robertson ◽

R. L. Jamison

Keyword(s):

Blood Flow ◽

Atrial Natriuretic Peptide ◽

Natriuretic Peptide ◽

Sodium Excretion ◽

Urine Flow ◽

Medullary Blood Flow ◽

Vasa Recta ◽

Renal Medullary Blood Flow ◽

Experimental Group ◽

Atrial Natriuretic

To determine whether synthetic atrial natriuretic peptide (ANP) increases renal medullary blood flow and if so whether the increase mediates the diuresis and natriuresis induced by ANP, inner medullary vasa recta blood flow in the exposed left renal papilla of anesthetized Munich Wistar rats weighing between 102 and 161 g was measured by fluorescence videomicroscopy. The rats were maintained in a euvolemic state by the infusion of albumin. Synthetic ANP (Auriculin B) was administered intravenously as 2.5 micrograms/kg body wt prime and as a continuous infusion of 0.2 microgram X min-1 X kg body wt-1 to the experimental group (n = 7). Within 2 min after ANP was given, urine flow and sodium excretion increased (29.4 +/- 3.8 to 50.4 +/- 5.8 microliter X min-1 X kidney wt-1, P less than 0.01, and 3.39 +/- 0.57 to 6.05 +/- 0.95 mueq X min-1 X g kidney wt-1, P less than 0.01, respectively), but vasa recta blood flow in descending (DVR) or ascending (AVR) vasa recta did not change significantly (9.5 +/- 2.3 to 10.0 +/- 2.8 nl/min in DVR and 5.3 +/- 1.0 to 6.1 +/- 1.2 nl/min in AVR). Forty-five minutes after ANP was begun, urine flow and sodium excretion increased further (77.1 +/- 11.1 microliter X min-1 X g kidney wt-1 and 12.0 +/- 2.15 mueq X min-1 X g kidney wt-1, respectively), and by this time vasa recta blood flow had increased significantly to 14.0 +/- 2.6 in DVR, P less than 0.01, and 9.8 +/- 1.2 in AVR, P less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)

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Role of renal medullary adenosine in the control of blood flow and sodium excretion

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1999.276.3.r790 ◽

1999 ◽

Vol 276 (3) ◽

pp. R790-R798 ◽

Cited By ~ 40

Author(s):

Ai-Ping Zou ◽

Kasem Nithipatikom ◽

Pin-Lan Li ◽

Allen W. Cowley

Keyword(s):

Blood Flow ◽

Sodium Excretion ◽

Renal Medulla ◽

Urine Flow ◽

Doppler Flowmetry ◽

Blood Flows ◽

Medullary Blood Flow ◽

Adenosine Concentration ◽

Interstitial Infusion

This study determined the levels of adenosine in the renal medullary interstitium using microdialysis and fluorescence HPLC techniques and examined the role of endogenous adenosine in the control of medullary blood flow and sodium excretion by infusing the specific adenosine receptor antagonists or agonists into the renal medulla of anesthetized Sprague-Dawley rats. Renal cortical and medullary blood flows were measured using laser-Doppler flowmetry. Analysis of microdialyzed samples showed that the adenosine concentration in the renal medullary interstitial dialysate averaged 212 ± 5.2 nM, which was significantly higher than 55.6 ± 5.3 nM in the renal cortex ( n = 9). Renal medullary interstitial infusion of a selective A1antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 300 pmol ⋅ kg−1 ⋅ min−1, n = 8), did not alter renal blood flows, but increased urine flow by 37% and sodium excretion by 42%. In contrast, renal medullary infusion of the selective A2 receptor blocker 3,7-dimethyl-1-propargylxanthine (DMPX; 150 pmol ⋅ kg−1 ⋅ min−1, n = 9) decreased outer medullary blood flow (OMBF) by 28%, inner medullary blood flows (IMBF) by 21%, and sodium excretion by 35%. Renal medullary interstitial infusion of adenosine produced a dose-dependent increase in OMBF, IMBF, urine flow, and sodium excretion at doses from 3 to 300 pmol ⋅ kg−1 ⋅ min−1( n = 7). These effects of adenosine were markedly attenuated by the pretreatment of DMPX, but unaltered by DPCPX. Infusion of a selective A3receptor agonist, N 6-benzyl-5′-( N-ethylcarbonxamido)adenosine (300 pmol ⋅ kg−1 ⋅ min−1, n = 6) into the renal medulla had no effect on medullary blood flows or renal function. Glomerular filtration rate and arterial pressure were not changed by medullary infusion of any drugs. Our results indicate that endogenous medullary adenosine at physiological concentrations serves to dilate medullary vessels via A2 receptors, resulting in a natriuretic response that overrides the tubular A1 receptor-mediated antinatriuretic effects.

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