Genetic disruption of atrial natriuretic peptide receptor-A alters renin and angiotensin II levels

We have studied cardiovascular and renal phenotypes in Npr1 (genetic determinant of natriuretic peptide receptor-A; NPRA) gene-disrupted mutant mouse model. The baseline systolic arterial pressure (SAP) in 0-copy mutant (-/-) mice (143 +/- 2 mmHg) was significantly higher than in 2-copy wild-type (+/+) animals (104 +/- 2 mmHg); however, the SAP in 1-copy heterozygotes (+/-) was at an intermediate value (120 +/- 4 mmHg). To determine whether Npr1 gene function affects the renin-angiotensin-aldosterone system (RAAS), we measured the components of RAAS in plasma, kidney, and adrenal gland of 0-copy, 1-copy, and 2-copy male mice. Newborn (2 days after the birth) 0-copy pups showed 2.5-fold higher intrarenal renin contents compared with 2-copy wild-type counterparts (0-copy 72 +/- 12 vs. 2-copy 30 +/- 7 microg ANG I. mg protein(-1). h(-1), respectively). The intrarenal ANG II level in 0-copy pups was also higher than in 2-copy controls (0-copy 33 +/- 5 vs. 2-copy 20 +/- 2 pg/mg protein, respectively). However, both young (3 wk) and adult (16 wk) 0-copy mutant mice showed a dramatic 50-80% reduction in plasma renin concentrations (PRCs) and in expression of renal renin message compared with 2-copy control animals. In contrast, the adrenal renin content and mRNA expression levels were 1.5- to 2-fold higher in 0-copy adult mice than in 2-copy animals. The results suggest that inhibition of renal and systemic RAAS is a compensatory response that prevents greater increases in elevated arterial pressures in adult NPRA null mutant mice. However, the greater renin and ANG II levels seen in 0-copy newborn pups provide evidence that the direct effect of NPRA activation on renin is an inhibitory response.

Enhancement of angiotensinogen expression in angiotensin II-dependent hypertension

Chronic infusion of angiotensin (Ang) II leads to the development of hypertension and enhances intrarenal Ang II content to levels greater than can be explained from the circulating concentrations of the peptide. We previously reported that renal angiotensinogen (Ao) mRNA is enhanced in Ang II-dependent hypertension and may contribute to augmented intrarenal Ang II levels, but the Ao protein levels were not significantly increased. Because a high-salt diet (H/S) has been shown to suppress renal expression of Ao mRNA, we examined the effects of chronic Ang II infusion on kidney and liver Ao mRNA and protein levels in male Sprague-Dawley rats (n=12) maintained on an 8% salt diet. Ang II was administered via osmotic minipumps (40 ng/min) to 1 group (n=6) while the remaining rats were sham-operated. A H/S diet alone did not alter systolic blood pressure in sham animals (109+/-6 mm Hg at day 12); however, Ang II infusions to the H/S rats significantly increased systolic blood pressure (167+/-7 at day 12) and intrarenal Ang II content (459+/-107 fmol/g versus 270+/-42) despite a marked suppression of plasma renin activity (0.9+/-0.2 ng Ang I. mL(-1). h(-1) versus 2.8+/-1.3). Ang II infusions significantly increased kidney Ao mRNA compared with the H/S diet alone by 1.9+/-0.1-fold. Western blot analysis of kidney protein extracts showed that the Ang II-infused rats had increased kidney Ao protein levels compared with the H/S diet alone (1.9+/-0.1-fold). Liver Ao mRNA and protein and plasma Ao protein were also significantly increased by Ang II infusions. These data demonstrate the effects of Ang II infusion to stimulate Ao mRNA and protein. Thus, the augmented intrarenal Ang II in Ang II-dependent hypertension may result, in part, by a positive amplification mechanism to activate renal expression of AO:

Nitric oxide in the control of renal hemodynamics and excretory function

Experimental evidence has now been amassed to indicate that inhibition of nitric oxide (NO) synthase reduces total or regional renal blood flow by approximately 25 to 30% and markedly increases the renal vascular resistance, demonstrating that basal release of NO helps to maintain the relatively low vascular resistance that is characteristic for the kidney. It has been demonstrated that intraarterial administration of NO synthase inhibitors causes marked reductions in sodium excretion without changes in filtered load and suppressed the arterial pressure-induced natriuretic responses in the kidney. We also demonstrated that a constant rate infusion of a NO donor in dogs pretreated with a NOS inhibitor resulted in increases in sodium excretion but failed to restore the slope of the relation between arterial pressure and sodium excretion, suggesting that an alteration in intrarenal NO production rate during changes in arterial pressure is involved in the mediation of pressure natriuresis. Further experiments in dogs performed in our laboratory have confirmed that there is a direct relationship between changes in arterial pressure and intrarenal NO activity measured using NO-sensitive microelectrodes in the renal tissue. These arterial pressure-induced changes in intrarenal NO activity were seen positively correlated with the changes in urinary excretion rates of sodium. Collectively, these data suggest that acute changes in arterial pressure alter intrarenal NO production, which inhibits tubular sodium reabsorption to manifest the phenomenon of pressure natriuresis.

Interactions of adenosine A1 and A2a receptors on renal microvascular reactivity

Adenosine vasoconstricts preglomerular arterioles via adenosine A1 receptors. Because adenosine also activates adenosine A2 receptors, its overall renal vascular actions are complex and not fully understood. The present study was performed to determine the relative contributions of adenosine A1 and A2a receptors to the responsiveness of the renal microvasculature to adenosine. Afferent and efferent arteriolar diameters were monitored in vitro using the blood-perfused rat juxtamedullary nephron preparation. Basal afferent and efferent arteriolar diameters averaged 17.1 +/- 0.5 (n = 35) and 17.8 +/- 0.5 (n = 20) microm, respectively. Superfusion with 0.1 and 1 micromol/l adenosine did not significantly alter afferent and efferent arteriolar diameters; however, 10 micromol/l adenosine significantly reduced afferent and efferent arteriolar diameters (-8.2 +/- 0.8 and -5.7 +/- 0.6%, respectively). The afferent and efferent arteriolar vasoconstrictor responses to adenosine waned at a dose of 100 micromol/l, such that diameters returned to values not significantly different from control within 2 min. During adenosine A1 receptor blockade with 8-noradamantan-3-yl-1,3-dipropylxanthine (KW-3902: 10 micromol/l), 10 and 100 micromol/l adenosine significantly increased afferent diameter by, respectively, 8.1 +/- 1.2 and 13.7 +/- 1.3% (n = 14) and efferent arteriolar diameter by 6.4 +/- 1.3 and 9.3 +/- 1.2% (n = 8). The afferent and efferent arteriolar vasodilatory responses to adenosine in the presence of KW-3902 were significantly attenuated by addition of the adenosine A2a receptor antagonist 1,3-dipropyl-7-methyl-8-(3,4-dimethoxystyryl)xanthine (KF-17837: 15 micromol/l, n = 7 and 6, respectively). The addition of KF-17837 alone significantly enhanced afferent (n = 15) and efferent (n = 6) arteriolar vasoconstrictor responses to 1, 10, and 100 micromol/l adenosine. These results indicate the presence of adenosine A1 and A2a receptors on afferent and efferent arterioles of juxtamedullary nephrons, such that adenosine A2a receptor-mediated vasodilation partially buffers adenosine-induced vasoconstriction in both pre- and postglomerular segments of the renal microvasculature.

Nitric oxide dependency of arterial pressure-induced changes in renal interstitial hydrostatic pressure in dogs

A direct relationship between renal arterial pressure (RAP) and renal interstitial hydrostatic pressure (RIHP) has been shown under conditions of efficient renal blood flow autoregulation. Experiments were performed in six anesthetized dogs to evaluate whether these RIHP responses to changes in RAP were modified during nitric oxide (NO) inhibition with nitro-L-arginine (NLA) or after administration of NO donor agents. A microtip catheter transducer was placed underneath the renal capsule to measure RIHP. Stepwise reductions in RAP (140 to 80 mm Hg) during control conditions resulted in decreases in RIHP from its basal value of 4.7+/-1.1 mm Hg with a slope of 0.04+/-0.026 mm Hg. mm Hg(-)(1) along with decreases in urinary nitrate/nitrite excretion rate (U(NOx)V). Renal cortical and medullary blood flows, measured by laser-Doppler flowmetry, exhibited high autoregulatory efficiency over this RAP range. The changes in RIHP during alterations in RAP were positively correlated (r=0.743; P:<0.001) with the changes in U(NOx)V but not with cortical or medullary blood flow. NLA infusion decreased RIHP to 1.9+/-0.5 mm Hg and also reduced U(NOx)V from 1.8+/-0.2 to 0.9+/-0.01 nmol. min(-)(1). g(-)(1). Infusion of NO donors restored RIHP (4.3+/-0.9 mm Hg) and U(NOx)V (1.5+/-0.2 nmol. min(-)(1). g(-)(1)). During NLA infusion, the RIHP responses to reductions in RAP were markedly attenuated and were not restored even during constant-rate infusion of NO donors. The results suggest that changes in RIHP in response to alterations in RAP are associated with changes in intrarenal NO, suggesting a direct effect of NO to regulate RIHP.

Renal interstitial atp responses to changes in arterial pressure during alterations in tubuloglomerular feedback activity

We recently demonstrated a direct relationship between autoregulation-related changes in renal vascular resistance (RVR) and renal interstitial ATP concentrations. To assess the possible role for extracellular ATP in the regulation of tubuloglomerular feedback (TGF)-mediated autoregulatory adjustments in RVR, renal interstitial ATP concentrations were measured with microdialysis probes in anesthetized dogs at different renal arterial pressures (RAPs) within the autoregulatory range during augmented and diminished activity of the TGF mechanism. Stepwise reductions in RAP from ambient pressure (129+/-3 mm Hg) to 102+/-2 mm Hg (step 1) and 75+/-1 mm Hg (step 2) resulted in significant decreases in ATP concentrations from 9.0+/-0.8 to 6.3+/-0.6 nmol/L in step 1 and to 4.2+/-0.5 nmol/L in step 2. Changes in RVR were highly correlated with changes in ATP concentrations (r=0.86, P<0.001, n=12). Acetazolamide (100 microgram. kg(-1). min(-1), n=6), which increases solute delivery to the macula densa, thus augmenting TGF activity, significantly decreased renal blood flow (RBF) by -16+/-2% and glomerular filtration rate (GFR) by -22+/-4% and increased ATP concentrations from 8.4+/-0.7 to 15.5+/-1.4 nmol/L. Although basal RBF and GFR levels were reduced by the acetazolamide infusion, autoregulation efficiency was maintained, and interstitial ATP concentrations were significantly decreased in response to reductions in RAP by -36+/-4% in step 1 and by -54+/-2% in step 2. The relationship between changes in RVR and interstitial ATP concentrations was preserved during acetazolamide treatment (r=0.80, P<0.01). Inhibition of the TGF mechanism by furosemide significantly increased RBF by 33+/-6% and GFR by 13+/-2% and decreased ATP concentrations from 8.9+/-1.4 to 5.0+/-0.8 nmol/L (n=6). Furosemide caused marked impairment of RBF and GFR autoregulatory efficiency (by -14+/-3% and -11+/-3% in step 1 and by -26+/-2% and -18+/-4% in step 2, respectively). In the furosemide-treated kidneys, interstitial ATP levels remained low and were not altered during reductions in RAP (4.7+/-0.7 nmol/L in step 1 and 4.7+/-0.8 nmol/L in step 2), and changes in RVR did not exhibit a correlation with changes in ATP concentrations (r=0.22, P=0.30). These data support the hypothesis that extracellular ATP contributes to autoregulatory adjustments in RVR that are mediated by changes in activity of the TGF mechanism.

Early diabetes mellitus stimulates proximal tubule renin mRNA expression in the rat

BACKGROUND

Enhanced intrarenal angiotensin II (Ang II) activity may contribute to diabetic nephropathy. The proximal tubule is a proposed site of significant intrarenal Ang II production. We determined the effect of early diabetes on mRNA expression of components of the proximal tubule renin-angiotensin system.

METHODS

Three groups of male Sprague-Dawley rats were studied after two weeks: (1) control (C), (2) streptozotocin-induced diabetes (STZ), and (3) STZ-induced diabetes, with normoglycemia maintained by insulin implants (STZ-I). Competitive reverse transcription-polymerase chain reaction was used to assay mRNA for renin, angiotensinogen, and angiotensin-converting enzyme in suspensions of proximal tubules; plasma and kidney levels of Ang II were measured by radioimmunoassay, and Western analysis of Ang II subtype 1 (AT1) receptors was performed.

RESULTS

STZ rats tended to have increased plasma and intrarenal levels of Ang II compared with C and STZ-I rats. In proximal tubules, mRNA for renin was significantly increased in STZ rats, with reversal to control values in STZ-I rats (C, 2432 +/- 437 vs. STZ, 5688 +/- 890 fg/0.25 microg RNA, P < 0.05 vs. C, N = 9, vs. STZ-I, 1676 +/- 376 fg/0.25 microg RNA, P = NS vs. C). In STZ rats, the AT1 receptor antagonist losartan caused a further fivefold increase in proximal tubule renin mRNA, associated with proximal tubular renin immunostaining. STZ had no significant effect on mRNA expression for angiotensinogen or angiotensin-converting enzyme in proximal tubules. By Western blot analysis, cortical and proximal tubule AT1 receptor protein expression was significantly decreased in STZ rats.

CONCLUSIONS

These data suggest activation of the proximal tubule renin-angiotensin system in early STZ diabetes, mediated at least partly by enhanced expression of renin mRNA. Increased local production of Ang II could contribute to tubulointerstitial injury in this model.

Dynamic interaction between myogenic and TGF mechanisms in afferent arteriolar blood flow autoregulation

The dynamic activity of afferent arteriolar diameter (AAD) and blood flow (AABF) responses to a rapid step increase in renal arterial pressure (100-148 mmHg) was examined in the kidneys of normal Sprague-Dawley rats (n = 11) before [tubuloglomerular feedback (TGF)-intact] and after interruption of distal tubular flow (TGF-independent). Utilizing the in vitro blood-perfused juxtamedullary nephron preparation, fluctuations in AAD and erythrocyte velocity were sampled by using analog-to-digital computerized conversion, video microscopy, image shearing, and fast-frame, slow-frame techniques. These assessments enabled dynamic characterization of the autonomous actions and collective interactions between the myogenic and TGF mechanisms at the level of the afferent arteriole. The TGF-intact and TGF-independent systems exhibited common initial (0-24 vs. 0-13 s, respectively) response slope kinetics (-0.53 vs. -0.47% DeltaAAD/s; respectively) yet different maximum vasoconstrictive magnitude (-11.28 +/- 0.1 vs. -7. 02 +/- 0.9% DeltaAAD; P < 0.05, respectively). The initial AABF responses similarly exhibited similar kinetics but differing magnitudes. In contrast, during the sustained pressure input (13-97 s), the maximum vasoconstrictor magnitude (-7.02 +/- 0.9% DeltaAAD) and kinetics (-0.01% DeltaAAD/s) of the TGF-independent system were markedly blunted whereas the TGF-intact system exhibited continued vasoconstriction with slower kinetics (-0.20% DeltaAAD/s) until a steady-state plateau was reached (-25.9 +/- 0.4% DeltaAAD). Thus the TGF mechanism plays a role in both direct mediation of vasoconstriction and in modulation of the myogenic response.

Roles of ANG II and bradykinin in the renal regional blood flow responses to ACE inhibition in sodium-depleted dogs

The relative contributions of ANG II and bradykinin (BK) to the renal regional blood flow responses during angiotensin-converting enzyme (ACE) inhibition remain unclear. This study was performed to evaluate renal cortical (CBF) and medullary blood flow (MBF) responses to intrarterial administration of enalaprilat (33 microg. kg(-1). min (-1)) after blockade of the ANG II AT(1 )receptors with candesartan (100 microg) in 7 dogs fed a low-salt diet (0.01%) for 5 days. Laser-Doppler flowmetry was used to measure relative changes in CBF and MBF. Candesartan alone increased CBF (+20 +/- 2%) and MBF (+22 +/- 7%). Enalaprilat infusion after candesartan administration resulted in further increases in both CBF (+21 +/- 5%) and MBF (+41 +/- 8%). However, the relative changes in MBF were significantly greater (P < 0.01) than those in CBF. Administration of the BK B(2) receptor blocker icatibant (300 microg) after enalaprilat returned CBF and MBF to values seen with candesartan alone. These data support a substantive role for BK potentiation during ACE inhibitor-induced renal vasodilation in dogs maintained on a low-sodium diet, with a relatively greater effect on MBF compared to CBF.

Impairment of pressure-natriuresis and renal autoregulation in ANG II-infused hypertensive rats

Chronic infusions of initially subpressor doses of angiotensin II (ANG II) lead to progressive hypertension over a 2-wk period and to augmented intrarenal ANG II levels. The present study was performed to investigate total renal blood flow (RBF) and medullary blood flow (MBF) autoregulatory behavior and pressure-natriuresis in ANG II-infused hypertensive rats and how these are modified by concomitant treatment with an ANG II AT(1) receptor antagonist. ANG II-infused rats (n = 27) were prepared by administration of ANG II at 60 ng/min via osmotic minipump for 13 days. Twelve of the ANG II-infused hypertensive rats were treated with losartan in the drinking water (30 mg. kg.(-1) day(-1)). Rats were anesthetized with pentobarbital sodium (50 mg/kg, ip) and prepared for renal function measurements. An aortic clamp was placed above the junction of the left renal artery to reduce renal arterial pressure. Autoregulatory responses for renal plasma flow, overall RBF, and glomerular filtration rate were impaired in ANG II-infused hypertensive rats; however, MBF autoregulation was not disrupted. Most strikingly, pressure-natriuresis was markedly suppressed in ANG II-infused hypertensive rats. Chronic treatment with losartan prevented the impairment of the pressure-natriuresis relationship caused by chronic ANG II infusion. These findings demonstrate that chronic ANG II infusion leads to marked impairment of sodium excretion and suppression of the pressure-natriuresis relationship, which may contribute to the progressive hypertension that occurs in this model. These renal effects are prevented by simultaneous treatment with an AT(1) receptor blocker.

Intrarenal angiotensin II augmentation in angiotensin II dependent hypertension

In several models of angiotensin II (ANG II) dependent hypertension, intrarenal ANG II levels increase to a much greater extent than the circulating levels even though the renal renin levels are decreased. The 2-kidney-1-clip (2K1C) Goldblatt rat model is particularly intriguing because hypertension develops in the presence of an intact kidney which would be expected to maintain sodium balance and protect against hypertension. Although the non-clipped kidney becomes renin depleted, it exhibits enhanced microvascular reactivity and increased tubular fractional sodium reabsorption. The non-clipped kidney ANG II content is either elevated or unchanged and proximal tubular fluid ANG II concentrations are not suppressed compared to the nanomolar concentrations found in normal rats. These results suggest that intrarenal ANG II content can be regulated independently of renal renin content. A similar hypertensive process occurs in rats infused chronically with low doses of ANG II. Renal ANG II content increases over 14 days to a greater extent than the circulating concentrations. Functionally, ANG II infused rats demonstrate reduced sodium excretion and marked suppression of pressure natriuresis. These ANG II dependent influences on kidney function contribute to the maintenance of hypertension. Renal augmentation of ANG II, hypertension, and suppressed sodium excretion are blocked by AT1 receptor blockers. To study the mechanisms responsible for intrarenal ANG II augmentation, we infused a different form of ANG II (Val5 ANG II), that can be separated from endogenous ANG II by HPLC. These results indicated that the increased renal ANG II content was due to accumulation of circulating ANG II in addition to continued production of endogenous ANG II. The renal accumulation of Val5-ANG II was markedly reduced by concomitant treatment with the AT1 receptor blocker, losartan. In addition, we found an unchanged overall ANG II-AT1 receptor protein which probably contributes to the maintained ANG II dependent influences. Collectively, the data support the concept that there is internalization of ANG II through an AT1 receptor mediated process and that some of the internalized ANG II is protected from degradation. The augmented intrarenal ANG II coupled with sustained levels of AT1 receptors contribute to the continued ANG II dependent suppression of renal function and sodium excretion thereby maintaining the hypertension.

Relation between renal interstitial ATP concentrations and autoregulation-mediated changes in renal vascular resistance

The present study was performed to examine the hypothesis that autoregulation-related changes in renal vascular resistance (RVR) are mediated by extracellular ATP. By use of a microdialysis method, renal interstitial concentrations of ATP and adenosine were measured at different renal arterial pressures (RAPs) within the autoregulatory range in anesthetized dogs (n=12). RAP was reduced in steps from the ambient pressure (131+/-4 mm Hg) to 105+/-3 mm Hg (step 1) and 80+/-2 mm Hg (step 2). Renal blood flow and glomerular filtration rate exhibited efficient autoregulation in response to these changes in RAP. RVR decreased by 22+/-2% in step 1 (P<0.01) and 38+/-3% in step 2 (P<0.01). The control renal interstitial concentration of ATP was 6.51+/-0.71 nmol/L and decreased to 4. 51+/-0.55 nmol/L in step 1 (P<0.01) and 2.77+/-0.47 nmol/L in step 2 (P<0.01). In contrast, the adenosine concentrations (117+/-6 nmol/L) were not altered significantly. Changes in ATP levels were highly correlated with changes in RVR (r=0.88, P<0.0001). Further studies demonstrated that stimulation of the tubuloglomerular feedback (TGF) mechanism by increasing distal volume delivery elicited with acetazolamide also led to increases in renal interstitial ATP concentrations, whereas furosemide, which is known to block TGF responses, reduced renal interstitial fluid ATP concentrations. The data demonstrate a positive relation between renal interstitial fluid ATP concentrations and both autoregulation- and TGF-dependent changes in RVR and thus support the hypothesis that changes in extracellular ATP contribute to the RVR adjustments responsible for the mechanism of renal autoregulation.

Nitric oxide-angiotensin II interactions in angiotensin II-dependent hypertension

Many studies indicate that renal haemodynamic function in angiotensin II- (ANG II) dependent hypertension is not reduced as much as would be predicted from the elevated ANG II levels suggesting that counteracting renoprotective mechanisms are activated. One important renoprotective effect is mediated by increased levels of nitric oxide. Recent studies using the ANG II-infused hypertensive rat model have shown that inhibition of nitric oxide synthesis (NOS) causes greater decreases in renal blood flow and glomerular filtration rate in ANG II-infused hypertensive rats than in control rats. This augmented nitric oxide-dependent influence is localized primarily in the cortex and to the preglomerular vasculature. The differential effects on the renal cortex and medulla are also reflected by the differences in NOS activities and protein expression. Ca2+-dependent NOS activity was significantly greater in the cortex but not the medulla of the ANG II-infused hypertensive rats compared with control rats. This was associated with marked activation of endothelial NOS protein levels and smaller increases in neuronal NOS protein levels in the cortex but not in the medulla. In contrast, the Ca2+-independent NOS activity and the inducible NOS protein levels in the cortex were significantly lower in the ANG II-infused hypertensive rats. These data support the hypothesis that cortical Ca2+-dependent NOS, primarily endothelial NOS, is stimulated during the early phases of ANG II-induced hypertension and exerts a renoprotective effect on cortical haemodynamics.

Renal responses to AT1 receptor blockade

Because of the importance of the renin-angiotensin system in the pathophysiology of hypertension and in mediating associated alterations in renal function, angiotensin II (Ang II) AT1 receptor blockers provide a direct means of protecting against influences of excessive Ang II levels. The kidney is an important site of action of Ang II AT1 receptor blockers because intrarenal Ang II not only vasoconstricts the renal vasculature but also reduces sodium excretion and suppresses the pressure natriuresis relationship. Even in normal conditions, intrarenal Ang II content is greater than can be explained on the basis of circulating Ang II and is compartmentalized with proximal tubule concentrations of Ang I and Ang II being several times higher than plasma concentrations. The localization of angiotensinogen in proximal tubule cells further supports the concept that the proximal tubule secretes Ang II or precursors of Ang II into the tubular fluid to activate luminal Ang II receptors. Recent immunohistochemical studies have demonstrated an abundance of AT1 receptors on the luminal surface of proximal and distal tubule cells as well as on vascular smooth muscle cells of afferent and efferent arterioles and on glomerular mesangial cells. Activation of luminal AT1 receptors stimulates the sodium hydrogen exchanger and increases reabsorption rate. The prominence of AT1 receptors in vascular and epithelial tissues in the kidney provides the basis for the powerful effects of AT1 receptor blockers on renal function especially in hypertensive conditions. In the two-kidney, one-clip (2K1C) Goldblatt hypertensive rat model, the nonclipped kidney is renin depleted but the intrarenal Ang II levels are not suppressed and Ang II concentrations in proximal tubular fluid remain high (10(-8) mol/L). AT1 receptor blockers such as candesartan have been shown to cause significant increases in glomerular filtration rate, renal blood flow and proportionately much greater increases in sodium excretion and fractional sodium excretion. Ang II blockade also markedly increases the slope of the pressure natriuresis relationship. The collective actions of Ang II blockers on tubular transport and renal hemodynamics provide long-term effects to regulate sodium balance, which contributes to the long-term control of hypertension.