Effects of dietary salt changes on renal  renin-angiotensin system in rats

Renin (RA) and angiotensin-converting enzyme (ACE) activities and angiotensinogen, ANG I, and ANG II levels were measured in the kidney (cortex and medulla) and plasma of Wistar-Kyoto rats on a low-sodium (LS; 0.025% NaCl; n= 8), normal-sodium (NS; 1% NaCl; n = 7), or high-sodium (HS; 8% NaCl; n = 7) diet for 21 days. RA, ANG I, and ANG II levels increased in a manner inversely related to sodium content of the diet in both plasma and renal tissues. The LS diet resulted in a 16-, 2.8-, and 1.8-fold increase in plasma RA, ANG I, and ANG II levels, respectively, compared with those in HS rats. In the renal cortex and medulla, RA, ANG I, and ANG II levels were also increased by diminution of dietary salt content but, in contrast to plasma, ANG II levels increased much more than RA or ANG I levels [5.4 (cortex)- and 4.7 (medulla)-fold compared with HS rats]. In summary, we demonstrated variations of ANG II levels in the kidney during dietary salt modifications. Our results confirm that RA and ACE activity are not the steps limiting intrarenal ANG II levels. Nevertheless, despite RA and ACE activity differences between renal cortex and medulla, ANG I and ANG II levels are equivalent in these two tissues; these results argue against a compartmentalization of RAS in these two intrarenal areas.

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High Na intake increases renal angiotensin II levels and reduces expression of the ACE2-AT2R-MasR axis in obese Zucker rats

AJP Renal Physiology ◽

10.1152/ajprenal.00097.2012 ◽

2012 ◽

Vol 303 (3) ◽

pp. F412-F419 ◽

Cited By ~ 24

Author(s):

Preethi Samuel ◽

Quaisar Ali ◽

Rifat Sabuhi ◽

Yonnie Wu ◽

Tahir Hussain

Keyword(s):

Sodium Intake ◽

Zucker Rats ◽

Kidney Cortex ◽

Complex Nature ◽

Ang Ii ◽

Pronounced Increase ◽

High Sodium ◽

High Sodium Intake ◽

Obese Rats ◽

Obese Zucker Rats

High sodium intake is known to regulate the renal renin-angiotensin system (RAS) and is a risk factor for the pathogenesis of obesity-related hypertension. The complex nature of the RAS reveals that its various components may have opposing effects on natriuresis and blood pressure regulation. We hypothesized that high sodium intake differentially regulates and shifts a balance between opposing components of the renal RAS, namely, angiotensin-converting enzyme (ACE)-ANG II-type 1 ANG II receptor (AT1R) vs. AT2-ACE2-angiotensinogen (Ang) (1–7)-Mas receptor (MasR), in obesity. In the present study, we evaluated protein and/or mRNA expression of angiotensinogen, renin, AT1A/BR, ACE, AT2R, ACE2, and MasR in the kidney cortex following 2 wk of a 8% high-sodium (HS) diet in lean and obese Zucker rats. The expression data showed that the relative expression pattern of ACE and AT1BR increased, renin decreased, and ACE2, AT2R, and MasR remained unaltered in HS-fed lean rats. On the other hand, HS intake in obese rats caused an increase in the cortical expression of ACE, a decrease in ACE2, AT2R, and MasR, and no changes in renin and AT1R. The cortical levels of ANG II increased by threefold in obese rats on HS compared with obese rats on normal salt (NS), which was not different than in lean rats. The HS intake elevated mean arterial pressure in obese rats (27 mmHg) more than in lean rats (16 mmHg). This study suggests that HS intake causes a pronounced increase in ANG II levels and a reduction in the expression of the ACE2-AT2R-MasR axis in the kidney cortex of obese rats. We conclude that such changes may lead to the potentially unopposed function of AT1R, with its various cellular and physiological roles, including the contribution to the pathogenesis of obesity-related hypertension.

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Functional expression of the renin-angiotensin system in human podocytes

AJP Renal Physiology ◽

10.1152/ajprenal.00475.2004 ◽

2006 ◽

Vol 290 (3) ◽

pp. F710-F719 ◽

Cited By ~ 86

Author(s):

Max C. Liebau ◽

D. Lang ◽

J. Böhm ◽

N. Endlich ◽

Martin J. Bek ◽

...

Keyword(s):

Renin Angiotensin System ◽

Functional Expression ◽

Kidney Cortex ◽

Receptor Subtypes ◽

Ang Ii ◽

Angiotensin Receptor ◽

Angiotensin System ◽

Renin Angiotensin ◽

Beneficial Effects ◽

Glomerular Proteinuria

Experimental and clinical studies impressively demonstrate that angiotensin-converting enzyme inhibitors (ACEI) and angiotensin receptor blockers (ARB) significantly reduce proteinuria and retard progression of glomerular disease. The underlying intraglomerular mechanisms are not yet fully elucidated. As podocyte injury constitutes a critical step in the pathogenesis of glomerular proteinuria, beneficial effects of ACEI and ARB may partially result from interference with a local renin-angiotensin system (RAS) in podocytes. The knowledge of expression and function of a local RAS in podocytes is limited. In this study, we demonstrate functional expression of key components of the RAS in differentiated human podocytes: podocytes express mRNA for angiotensinogen, renin, ACE type 1, and the AT1 and AT2 angiotensin receptor subtypes. In Western blot experiments and immunostainings, expression of the AT1 and AT2 receptor was demonstrated both in differentiated human podocytes and in human kidney cortex. ANG II induced a concentration-dependent increase in cytosolic Ca2+ concentration via AT1 receptors in differentiated human podocytes, whereas it did not increase cAMP. Furthermore, ANG II secretion was detected, which was blocked by neither the ACEI captopril nor the renin inhibitor remikiren nor the chymase inhibitor chymostatin. ANG II secretion of podocytes was not increased by mechanical stress. Finally, ANG II was found to increase staurosporine-induced apoptosis in podocytes. We speculate that ACEI and ARB exert their beneficial effects, in part, by interfering with a local RAS in podocytes. Further experiments are required to identify the underlying molecular mechanism(s) of podocyte protection.

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Abstract P104: Renin Angiotensin System (RAS) Modulation in Hypertension Program by Maternal Intrauterine Malnutrition

Hypertension ◽

10.1161/hyp.66.suppl_1.p104 ◽

2015 ◽

Vol 66 (suppl_1) ◽

Author(s):

Rafael S Banti ◽

Rodrigo Yokota ◽

Danielle S Aragão ◽

Adriana Souza ◽

Amanda Pedroso ◽

...

Keyword(s):

Blood Pressure ◽

Renin Angiotensin System ◽

Control Group ◽

Ang Ii ◽

Alternative Pathways ◽

Angiotensin Peptides ◽

Increased Risk ◽

Ace Activity ◽

Intrauterine Malnutrition ◽

Group D

Intrauterine malnutrition (IM) during the early stages of development can alter the function of organs and tissues and can predict a lifetime of increased risk for adverse health outcomes, such as diabetes and hypertension. The kidney plays a key role in the development of hypertension programmed by IM, with the participation of the RAS. Our objectives were to study ACE activity and angiotensin peptides levels in tissues. Pregnants Wistar rats were separated into two groups: control group (C), fed ad libitum, and malnourished group (D) submitted to food restriction (diet 50% of the amount of feed consumed by the group C). After birth the offspring were kept as experimental groups C and D, respectively. At 4 months of age, the animals were sacrificed, heart and kidney tissues were collected to quantify angiotensin peptides and ACE activity. The offspring born with low birth weight. Kidney ACE activity was higher in group D compared to group C (299 ±86.7 vs. 253.4 ±84.82 mU/mg, p<0.05), differing from Heart (D versus C: 0.15 ± 0.08 vs. 0.24 ±0.09 mU/mg). Group D presented high blood pressure values compared to group C (140.6 ±2.8 vs. 124,3±2.6 mmHg). Kidney and heart Ang II levels were increased in group D being significant when compared to group C (238.26 ±25.1 vs. 161.85 ±45.6 pmol/g and 397.89±74.9 vs. 223.33±48.7 pmol/g, p<0.05, respectively). The same was observed for Ang I. The vasodilator peptide Ang1-7 levels in group D from kidney and heart were lower in comparison with group C, thus emphasizing an enabling environment for hypertension (220.74 ± 48.74 vs. 288.09 ± 47 pmol/g and 152.1±41.2 pmol/g vs. 228.93±41.2 pmol/g, p<0.05, respectively). Our results indicate that perturbed maternal nutritional status alters tissue RAS resulting in higher blood pressure in the offspring, demonstrated by increased renal ACE activity and Ang II levels, with reduced Ang 1-7. The increase of Ang I and II in the heart, despite low ACE activity in this tissue suggests the activation of RAS alternative pathways. This study describes for the first time that low levels of Ang 1-7 contributed to the early development of hypertension.

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Abstract 227: The Protective Effect of Kidney-Specific ACE Inhibition Against Chronic Angiotensin II Infusions is Associated with Blunted Intrarenal Renin-Angiotensin System Activation

Hypertension ◽

10.1161/hyp.60.suppl_1.a227 ◽

2012 ◽

Vol 60 (suppl_1) ◽

Author(s):

Jorge F Giani ◽

Tea Djandjoulia ◽

Nicholas Fetcher ◽

Sebastien Fuchs ◽

Dale M Seth ◽

...

Keyword(s):

Renin Angiotensin System ◽

Fold Increase ◽

Ace Inhibition ◽

Sham Operation ◽

Ang Ii ◽

Angiotensin System ◽

Renin Angiotensin ◽

Intrarenal Ras ◽

Failed Induction

Introduction: The responses to chronic angiotensin (Ang) II infusions of gene-targeted mice lacking kidney angiotensin-converting enzyme (ACE), in terms of intrarenal Ang II accumulation, hypertension, sodium and water retention are all blunted or absent. The objective of this study was to determine if these reduced responses were associated with changes in the intrarenal renin-angiotensin system (RAS). METHODS: Mice lacking intrarenal ACE (ACE10/10) were generated by targeted homologous recombination placing the expression of ACE only in macrophages. As a result, these mice have normal circulating ACE levels, but no kidney ACE. Wild-type (WT) mice of the same background (C57Bl/J) served as controls. Mice were subjected to sham-operation or subcutaneous infusion of Ang II for two weeks (n=6-10, 400 ng/kg/min via osmotic minipump). Mean arterial pressure (MAP) was followed by telemetry. At the end of the experiment, the kidneys were collected for analysis. Ang II content was measured by RIA. Renal abundance of ACE, angiotensinogen (AGT) and Ang II receptor type 1 (AT1R) were determined by Western Blot in total kidney homogenates. Results: At baseline, the MAP of WT and ACE 10/10 mice was similar 110 ± 4 mmHg vs. 109 ± 3 mmHg respectively (p>0.05). However, when subjected to chronic Ang II infusions, the hypertensive response was blunted in ACE 10/10 mice (129 ± 6 mmHg) vs. WT (146 ± 5 mmHg; P<0.05). Also, intrarenal Ang II accumulation was lower in ACE10/10 mice (724 ± 81 fmol/g) vs. WT (1130 ± 105 fmol/g, p<0.05). In non-treated mice, intrarenal RAS components analysis revealed that the absence of ACE in ACE10/10 mice was accompanied by a significant reduction in AGT (0.41 ± 0.06) and increased AT1R expression (1.32 ± 0.05) when compared to WT (normalized to 1.00, p<0.05 in both instances). Importantly, after chronic Ang II infusions, AGT, ACE and AT1R expression increased in WT (1.36, 1.26 and 1.17 fold increase respectively compared to non-treated WT, p<0.05) but not in the ACE10/10 mice (1.19, 1.06, 0.89 fold increase respectively compared to non-treated ACE10/10, p>0.05). Conclusion: The blunted hypertension and Ang II accumulation of mice devoid of kidney ACE in response to Ang II infusions is associated with a failed induction of renal AGT and the AT1R.

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In vitro production of angiotensin II by isolated glomeruli

AJP Renal Physiology ◽

10.1152/ajprenal.1995.268.2.f266 ◽

1995 ◽

Vol 268 (2) ◽

pp. F266-F272 ◽

Cited By ~ 5

Author(s):

B. A. Atiyeh ◽

B. S. Arant ◽

W. L. Henrich ◽

M. G. Seikaly

Keyword(s):

Angiotensin Ii ◽

Incubation Medium ◽

Renin Angiotensin System ◽

Ang Ii ◽

In Vitro Production ◽

Vascular Control ◽

Isolated Glomeruli ◽

Salt Depletion ◽

Wistar Kyoto

The glomerulus has several components of the renin-angiotensin system (RAS). The purpose of this study was to evaluate the ability of glomeruli isolated from adult Wistar-Kyoto rats to produce angiotensin II (ANG II). When isolated glomeruli were incubated in Krebs buffer, the peak concentration of immunoreactive angiotensin (ANG) in the incubation medium, representing simultaneous production and degradation, occurred after 15 min of incubation (3.98 +/- 0.34 pg.mg protein-1.15 min-1, of which 18% was ANG II. When 125I-labeled ANG II was incubated with isolated glomeruli, the half-life of ANG II was 6.06 min. Hence, we estimated ANG II production at 3.77 +/- 0.21 pg.mg protein-1.15 min-1. When angiotensinogen-rich serum was added to the incubation medium, ANG concentration at 15 min increased by 500-fold (1,978 +/- 44 pg.mg protein-1.15 min-1, P < 0.001). ANG concentration in the glomerular incubate responded to perturbations known to alter systemic RAS. Enalaprilat, chymostatin, propranolol, and renin antiserum decreased ANG concentration in glomerular incubate, whereas salt depletion increased this (P < 0.05). We conclude that the rat glomerulus can generate ANG II independent of neural, hormonal, or vascular control.

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Renal endosomes contain angiotensin peptides, converting enzyme, and AT1A receptors

AJP Renal Physiology ◽

10.1152/ajprenal.1999.277.2.f303 ◽

1999 ◽

Vol 277 (2) ◽

pp. F303-F311 ◽

Cited By ~ 41

Author(s):

John D. Imig ◽

Gabriel L. Navar ◽

Li-Xian Zou ◽

Katie C. O’Reilly ◽

Patricia L. Allen ◽

...

Keyword(s):

High Salt ◽

Dietary Sodium ◽

Kidney Cortex ◽

Ang Ii ◽

Converting Enzyme ◽

High Salt Diet ◽

Salt Diet ◽

Angiotensin Peptides ◽

Low Salt ◽

Ace Activity

Kidney cortex and proximal tubular angiotensin II (ANG II) levels are greater than can be explained on the basis of circulating ANG II, suggesting intrarenal compartmentalization of these peptides. One possible site of intracellular accumulation is the endosomes. In the present study, we tested for endosomal ANG I, ANG II, angiotensin type 1A receptor (AT1A), and angiotensin converting enzyme (ACE) activity and determined whether these levels are regulated by salt intake. Male Sprague-Dawley rats were fed chow containing either high or low dietary sodium for 10–14 days. Blood and kidneys were harvested and processed for measurement of plasma, kidney, and renal intermicrovillar cleft and endosomal angiotensin levels. Kidney ANG I averaged 179 ± 20 fmol/g and ANG II averaged 258 ± 36 fmol/g in rats fed a high-sodium diet and were significantly higher, averaging 347 ± 58 fmol/g and 386 ± 55 fmol/g, respectively, in rats fed a low-salt diet. Renal intermicrovillar clefts and endosomes contained ANG I and ANG II. Intermicrovillar cleft ANG I and ANG II levels averaged 8.4 ± 2.6 and 74 ± 26 fmol/mg, respectively, in rats fed a high-salt diet and 7.6 ± 1.7 and 70 ± 25 fmol/mg in rats fed a low-salt diet. Endosomal ANG I and ANG II levels averaged 12.3 ± 4.4 and 43 ± 19 fmol/mg, respectively, in rats fed a high-salt diet, and these levels were similar to those observed in rats fed a low-salt diet. Renal endosomes from rats fed a low-salt diet demonstrated significantly more AT1A receptor binding compared with rats fed a high-salt diet. ACE activity was detectable in renal intermicrovillar clefts and was 2.5-fold higher than the levels observed in renal endosomes. Acute enalaprilat treatment decreased ACE activity in renal intermicrovillar clefts by 90% and in renal endosomes by 84%. Likewise, intermicrovillar cleft and endosomal ANG II levels decreased by 61% and 52%, respectively, in enalaprilat-treated animals. These data demonstrate the presence of intact angiotensin peptides and ACE activity in renal intermicrovillar clefts and endosomes, indicating that intact angiotensin peptides are formed and/or trafficked through intracellular endosomal compartments and are dependent on ACE activity.

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Inhibitory effects of angiotensin-(1–7) on the nerve stimulation-induced release of norepinephrine and neuropeptide Y from the mesenteric arterial bed

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00400.2009 ◽

2010 ◽

Vol 298 (2) ◽

pp. H457-H465 ◽

Cited By ~ 14

Author(s):

Mirnela Byku ◽

Heather Macarthur ◽

Thomas C. Westfall

Keyword(s):

Neuropeptide Y ◽

Receptor Antagonist ◽

Renin Angiotensin System ◽

Sympathetic Nerves ◽

Ang Ii ◽

Spontaneously Hypertensive ◽

Angiotensin Type 2 Receptor ◽

Mesenteric Arterial Bed ◽

Wistar Kyoto

Neuropeptide Y (NPY) is a cotransmitter with norepinephrine (NE) and ATP in sympathetic nerves. There is evidence for increased activity of the sympathetic nervous system and the renin-angiotensin system (RAS), as well as a role for NPY in the development of hypertension in experimental animal models and in humans. Angiotensin II (ANG II) is known to facilitate sympathetic neurotransmission, an effect greater in spontaneously hypertensive rats (SHR) than normotensive Wistar-Kyoto (WKY) rats. A newly discovered product of the RAS is angiotensin-(1–7) [ANG-(1–7)]. There is evidence suggesting that ANG-(1–7) opposes the actions of ANG II, resulting in hypotensive effects. The objective of this study was to investigate the role of ANG-(1–7) on the nerve-stimulated overflow of NE and NPY from the mesenteric arterial bed of SHR and the mechanisms involved in mediating any effects produced. ANG-(1–7) (0.001, 0.01, 0.1 μM) decreased nerve-stimulated NE and NPY overflow, as well as perfusion pressure in preparations obtained from SHR. This effect was greater in preparations of SHR than WKY controls. In addition, ANG-(1–7) decreased NE overflow to a greater extent than NPY overflow. Administration of the Mas receptor antagonist, d-Ala7 ANG-(1–7), attenuated the decrease in both NE and NPY overflow due to ANG-(1–7) administration. However, the angiotensin type 2 receptor antagonist, PD-123391, attenuated the effect of ANG-(1–7) on NE overflow without affecting the decrease in NPY overflow. Moreover, in the presence of NG-nitro-l-arginine methyl ester, ANG-(1–7) decreased NPY overflow, but not NE overflow. ANG-(1–7) decreases the nerve-stimulated overflow of NE and NPY in preparations of SHR, whereas ANG II enhances it. Therefore, ANG-(1–7) may counteract the effects of ANG II by acting on ANG type 2 and Mas receptors.

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Modulation of the intrahepatic renin–angiotensin system after stimulation of the gastric sodium monitor in the rat

Clinical Science ◽

10.1042/cs0980057 ◽

1999 ◽

Vol 98 (1) ◽

pp. 57-64

Author(s):

V. Z. C. YE ◽

K. A. DUGGAN

Keyword(s):

Renin Angiotensin System ◽

Ang Ii ◽

Sprague Dawley ◽

Angiotensin System ◽

Low Sodium Diet ◽

Low Sodium ◽

Sprague Dawley Rats ◽

Sodium Load ◽

Ace Activity ◽

Stimulation Of

Changes in the rate of formation of angiotensin II (ANG II) participate in mediating the natriuresis that occurs in direct response to a gastric sodium stimulus (upper-gut sodium monitor). As this natriuresis is also dependent on intrahepatic events, we investigated whether changes in hepatic and plasma angiotensinogen levels and hepatic angiotensin-converting enzyme (ACE) activity might explain the decrease in ANG II synthesis. Male Sprague–Dawley rats, equilibrated on a low-sodium diet, were anaesthetized and received a sodium load of 1.5 mmol/kg (using 3× normal saline) either intragastrically or intravenously. Blood and livers were sampled before and at various times after sodium administration. ACE activity in serum and tissues was determined by generation of histidyl-leucine. Angiotensinogen was determined by radioimmunoassay of angiotensin I generated by incubation in the presence of exogenous renin. Plasma angiotensinogen had decreased significantly by 15 min after sodium administration (P< 0.005), while hepatic angiotensinogen was also decreased significantly from 30 min after the sodium load (P< 0.01). Hepatic ACE activity decreased in response to sodium (P< 0.005) from 30 min. We conclude that stimulation of the gastric sodium monitor regulates angiotensinogen synthesis and secretion by the liver, as well as hepatic ACE activity.

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An angiotensin-(1–7) peptidase in the kidney cortex, proximal tubules, and human HK-2 epithelial cells that is distinct from insulin-degrading enzyme

AJP Renal Physiology ◽

10.1152/ajprenal.00609.2014 ◽

2015 ◽

Vol 308 (6) ◽

pp. F594-F601 ◽

Cited By ~ 11

Author(s):

Bryan A. Wilson ◽

Nildris Cruz-Diaz ◽

Allyson C. Marshall ◽

Nancy T. Pirro ◽

Yixin Su ◽

...

Keyword(s):

Epithelial Cells ◽

Specific Activity ◽

Renin Angiotensin System ◽

Kidney Cortex ◽

Peptidase Activity ◽

Ang Ii ◽

Insulin Degrading Enzyme ◽

Angiotensin System ◽

Degrading Enzyme ◽

Thimet Oligopeptidase

Angiotensin 1–7 [ANG-(1–7)] is expressed within the kidney and exhibits renoprotective actions that antagonize the inflammatory, fibrotic, and pro-oxidant effects of ANG II. We previously identified an peptidase that preferentially metabolized ANG-(1–7) to ANG-(1–4) in the brain medulla and cerebrospinal fluid (CSF) of sheep (Marshall AC, Pirro NT, Rose JC, Diz DI, Chappell MC. J Neurochem 130: 313–323, 2014); thus the present study established the expression of the peptidase in the kidney. Utilizing a sensitive HPLC-based approach, we demonstrate a peptidase activity that hydrolyzed ANG-(1–7) to ANG-(1–4) in the sheep cortex, isolated tubules, and human HK-2 renal epithelial cells. The peptidase was markedly sensitive to the metallopeptidase inhibitor JMV-390; human HK-2 cells expressed subnanomolar sensitivity (IC50 = 0.5 nM) and the highest specific activity (123 ± 5 fmol·min−1·mg−1) compared with the tubules (96 ± 12 fmol·min−1·mg−1) and cortex (107 ± 9 fmol·min−1·mg−1). The peptidase was purified 41-fold from HK-2 cells; the activity was sensitive to JMV-390, the chelator o-phenanthroline, and the mercury-containing compound p-chloromercuribenzoic acid (PCMB), but not to selective inhibitors against neprilysin, neurolysin and thimet oligopeptidase. Both ANG-(1–7) and its endogenous analog [Ala1]-ANG-(1–7) (alamandine) were preferentially hydrolyzed by the peptidase compared with ANG II, [Asp1]-ANG II, ANG I, and ANG-(1–12). Although the ANG-(1–7) peptidase and insulin-degrading enzyme (IDE) share similar inhibitor characteristics of a metallothiolendopeptidase, we demonstrate marked differences in substrate specificity, which suggest these peptidases are distinct. We conclude that an ANG-(1–7) peptidase is expressed within the renal proximal tubule and may play a potential role in the renal renin-angiotensin system to regulate ANG-(1–7) tone.

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Renal renin-angiotensin system in diabetes: functional, immunohistochemical, and molecular biological correlations

AJP Renal Physiology ◽

10.1152/ajprenal.1993.265.4.f477 ◽

1993 ◽

Vol 265 (4) ◽

pp. F477-F486 ◽

Cited By ~ 44

Author(s):

S. Anderson ◽

F. F. Jung ◽

J. R. Ingelfinger

Keyword(s):

Renin Angiotensin System ◽

Plasma Renin ◽

Hydraulic Pressure ◽

Ang Ii ◽

Glomerular Injury ◽

Renal Vasculature ◽

Angiotensin System ◽

Renin Angiotensin ◽

Ace Activity ◽

Immunohistochemical Studies

Recent evidence indicates a role for the renin-angiotensin system (RAS) in the pathogenesis of glomerular injury in diabetes. To further explore the RAS in diabetes, studies were conducted in nondiabetic control rats and in moderately hyperglycemic diabetic (DM) rats. In DM rats, both acute and chronic therapy with the specific angiotensin II (ANG II) receptor antagonist losartan did not affect glomerular hyperfiltration or hyperperfusion but selectively normalized the glomerular capillary hydraulic pressure and ultrafiltration coefficient. To determine the basis of intrarenal hemodynamic responsiveness to RAS inhibition, we conducted biochemical, molecular biological, and immunohistochemical studies to assess endogenous RAS activity. Values for plasma renin concentration and serum angiotensin-converting enzyme (ACE) activity in DM rats were normal. In contrast, intrarenal renin protein content, and renin and angiotensinogen mRNAs, were increased in DM rats, suggesting disproportionate activation of the intrarenal RAS. Total renal ACE activity was significantly reduced in DM rats, but immunohistochemical studies indicated redistribution of ACE in the diabetic kidney. Proximal tubule ACE activity was reduced, but ACE immunostaining intensity was enhanced in glomeruli and renal vasculature. Together, these observations indicate increased RAS activity in those sites (glomeruli and vasculature) most likely to regulate hemodynamic function, potentially explaining the prominent responses to pharmacological blockade of ANG II formation and/or action.

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