Converting enzyme inhibition and renal tissue angiotensin II in the rat

Effect of blockade of endogenous angiotensin II on baroreflex function in conscious diabetic rats

Little is known about baroreflex control of renal nerve sympathetic activity (RSNA) or the effect of angiotensin II (ANG II) on the baroreflex in diabetes. We examined baroreflex control of RSNA and heart rate (HR) in conscious, chronically instrumented rats 2 wk after citrate vehicle (normal) or 55 mg/kg iv streptozotocin (diabetic) before and after losartan (5 mg/kg iv) or enalapril (2.5 mg/kg iv). Resting HR and RSNA were lower in diabetic versus normal rats. The range of baroreflex control of HR and the gain of baroreflex-mediated bradycardia were impaired in diabetic rats. Maximum gain was unchanged. The baroreflex control of RSNA was reset to lower pressures in the diabetic rats but remained otherwise unchanged. Losartan decreased mean arterial pressure (MAP) and increased HR and RSNA in both groups but had no influence on the baroreflex. Enalapril decreased MAP only in normal rats, yet the increase in HR and RSNA was similar in both groups. Thus in diabetic rats enalapril produced a pressure-independent increase in HR and RSNA. Enalapril exerted no effect on the baroreflex control of HR or RSNA in either group. These data indicate that in conscious rats resting RSNA is lower but baroreflex control of RSNA is preserved after 2 wk of diabetes. At this time, the baroreflex control of HR is already impaired and blockade of endogenous ANG II does not improve this dysfunction.

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.

Association of the D allele of the angiotensin I converting enzyme polymorphism with malignant vascular injury

AIMS

To determine whether there is an association between the insertion/deletion (I/D) polymorphism of the human angiotensin I converting enzyme (ACE) gene and malignant vascular injury (MVI).

METHODS

The polymerase chain reaction was used to genotype DNA extracted from archival, paraffin wax embedded renal biopsy material from 48 patients with MVI, made up from cases of malignant hypertension (n = 23), scleroderma (n = 10), and haemolytic uraemic syndrome (n = 15), and from whole blood samples from 191 healthy controls.

RESULTS

The D allele was found more frequently in cases of MVI than in healthy controls, (65% v 52%). Both the DD and I/D genotypes occurred significantly more frequently in patients with MVI than did the II genotype (chi(2) = 7.26, p = 0.007; and chi(2) = 4.06, p = 0.04, respectively).

CONCLUSIONS

Possession of at least one copy of the D allele is associated with an increased risk of developing MVI. Our data support a dominant mode of effect for the D allele. Use of the I/D polymorphism as a genetic marker for MVI may be of value clinically in identifying at risk individuals before the development of target end organ damage. Furthermore, those at risk may benefit from early ACE inhibition.

Angiotensin receptor blockers in diabetic nephropathy

Where shall we place angiotensin receptor blockers in the scheme of the prevention of diabetic nephropathy? Only the results of a large, randomized double-blind trial with a comparable and appropriate alternative would prove therapeutic efficacy. The results of several trials with angiotensin-converting enzyme (ACE) inhibitors have proven them to be the standard of care for diabetics and their kidneys. As reviewed in this article, the results of three large such clinical trials have recently been completed with angiotensin receptor blockers in patients with type 2 diabetes mellitus. Initial results appear favorable. However, whether angiotensin blockers have more to offer than ACE inhibitors is still speculative. The renin-angiotensin system plays an important role in the pathogenesis of diabetic nephropathy. Since alternative pathways to ACE have been uncovered in the formation of angiotensin II, inhibition at the final end point would provide favored blockade. Because angiotensin receptor blockers do provide this specific blockade, they offer far more promise than ACE inhibitors.

Angiotensin-converting enzyme (ACE) I/D genotype and renal ACE gene expression

BACKGROUND

The angiotensin-converting enzyme (ACE) I/D genotype affects serum ACE levels and the onset and progression of renal disease, but little is known about the mechanism. We investigated a possible association between the ACE I/D genotype and renal ACE mRNA levels in healthy subjects.

METHODS

Renal biopsy samples were obtained from 50 healthy kidney donors. The ACE I/D genotype was determined by polymerase chain reaction (PCR). Renal ACE mRNA quantification was performed by competitive RNA-PCR. In situ hybridization (ISH) for ACE mRNA on renal biopsy specimens was also performed.

RESULTS

The number of ACE transcripts in 100 ng of total RNA was significantly (P < 0.01) lower in subjects with II genotype (5.6 +/- 5.3 x 10(5), N = 20) compared with those with the ID (17.9 +/- 13.6 x 10(5), N = 23) or the DD genotype (36.9 +/- 14.6 x 10(5), N = 7) in healthy donors. The ISH studies showed that both tubular and glomerular ACE mRNA expressions were weak in subjects with the II genotype, intermediate in subjects with ID genotype, and strong in subjects with DD genotype.

CONCLUSIONS

It is suggested that renal ACE gene expression is associated with the ACE I/D genotype in healthy Japanese subjects.

Angiotensin-converting enzyme gene insertion/deletion polymorphism and renal damage in childhood uropathies

BACKGROUND

The activation of the renin-angiotensin system in various renal disorders is well established. Congenital urological abnormalities, such as obstruction and reflux, are common causes of renal failure in children contributing to approximately 25% of chronic renal failure in this age group. While the outlook relates to the severity of initial renal damage, there is considerable heterogeneity in renal parenchymal destruction among individuals and the reasons for this heterogeneity are not fully understood. A polymorphism within intron 16 of the angiostensin-converting enzyme (ACE) gene has been shown to influence the activity of the renin-angiotensin system, thus, it may also have an impact on the expression of renal disorders. We have determined the incidence of this ID polymorphism of the ACE gene in 47 Kuwaiti children with different urological abnormalities leading to variable degrees of renal impairment and in 48 healthy control subjects with a similar ethnic background.

METHODS

Blood samples were collected from the patients (n = 47) and controls (n = 48), total genomic DNA extracted and the ACE genotypes were determined using a polymerase chain reaction-based method.

RESULTS

The DD genotype was detected in 27/47 (57%) cases compared with 25/48 (52%) controls (P = 0.439). The heterozygous genotype ID was found in 14/47 (29%) cases compared with 22/48 (46%) controls (P = 0.0138). The homozygous II genotype was detected in 6/47 (13%) cases compared with 1/48 (2%) controls (P = 0.0247). The D allele of ACE gene was detected in 41/47 (87%) uropathy cases when individuals with homozygous DD and heterozygous ID genotypes were considered collectively. The incidence of parenchymal damage was considerably higher in uropathy cases with DD genotype (62%) compared with those having ID (26%) and II (12%) genotypes.

CONCLUSIONS

Our data suggest an association of D allele of the ACE gene insertion/deletion polymorphism and congenital urological abnormalities, which result in parenchymal damage in Kuwaiti Arab children.

Effect of ACE inhibition on pressor, renal vascular, and adrenal responses to infusion of angiotensin I in normal subjects eating a low-salt diet

To examine the influence of angiotensin-converting enzyme (ACE) on pressor, renal vascular, and adrenal responses during angiotensin I (Ang I) infusion, we studied 10 normotensive, healthy men. Each was in balance with a 10-mEq sodium, 100-mEq potassium intake and was studied before and during ACE inhibition with enalapril. Ang I (3, 10, and 30 ng/kg/min) was infused in each subject. Then ACE inhibition was instituted with enalapril for 3 days, which induced the anticipated fall in blood pressure, plasma Ang II, and aldosterone concentration, and rise in renal plasma flow. During ACE inhibition only the 30-ng/kg/min Ang I dose raised plasma Ang II levels. There was a spectrum, however, in the end-organ response to Ang I during ACE inhibition. Responses of plasma aldosterone concentration and blood pressure were in excellent accord with the reduction in Ang II formation. On the other hand, responses of the renal blood supply were substantially less inhibited than anticipated. Under the conditions of this study, ACE inhibition led to nonuniform changes in the response to exogenous Ang I, suggesting intrarenal conversion of Ang I to Ang II.

Greater blood pressure-lowering effect of the renin inhibitor EMD 58265 than an angiotensin-converting enzyme inhibitor in two-kidney one-clip Goldblatt rabbit

1. Renin inhibitors may be more advantageous than either angiotensin-converting enzyme (ACE) inhibitors or angiotensin (Ang) antagonists in blocking the renin-angiotensin system (RAS) because they do not allow accumulation of either AngI or AngII in plasma. 2. Effects of i.v. administration of two human renin inhibitors (EMD 58265 and U 71038) were compared with the ACE inhibitor enalaprilat on mean blood pressure (BP), renal blood flow (RBF) and plasma AngI and AngII in the anaesthetized two-kidney one-clip Goldblatt rabbit. 3. At doses of 2-2.5 mg/kg, i.v., EMD 58265 and 5-10 mg/kg, i.v., U 71038, both drugs decreased BP approximately 10 mmHg more than enalaprilat (2-4 mg/kg, i.v.) when given either before or after the ACE inhibitor. None of the three agents had any significant effect on RBF in the face of the lowered BP; however, renal vascular resistance was decreased. A higher dose of enalaprilat (10 mg/kg, i.v.) had no further effect on BP than the lower doses but did cause a marked increase in RBF. 4. Both renin inhibitors markedly decreased plasma AngI, but the high basal level of AngII was less consistently and only modestly affected. Enalaprilat, in either the low dose range or at the high dose, was also not effective in significantly decreasing AngII. 5. The results indicate that renin inhibition in the rabbit with a high circulating AngII level is more effective in lowering BP than ACE inhibition. A high dose of the ACE inhibitor may be required to block the intrarenal RAS, which may account for the increase in RBF.

Angiotensin-converting enzyme gene I/D polymorphism and carotid artery disease in renovascular hypertension

There is evidence linking the activation of the renin-angiotensin system (RAS) with target organ damage in renovascular hypertension (RVH). A genetic association of the DD genotype of the angiotensin-converting enzyme (ACE) gene with cardiovascular complications has been found in various clinical conditions. The aim of our study was to determine whether the insertion/deletion (I/D) polymorphism of the ACE gene is associated with the high prevalence of target organ damage reported in RVH. A total of 65 atherosclerotic patients (age 68.2 +/- 5.2 years) with RVH and 49 atherosclerotic patients (age 68.0 +/- 6.3 years) with essential hypertension (EH) were sequentially enrolled when attending the outpatient clinic for specialist assessment of their vascular disorder. Cardiac, renal, and vascular involvement were assessed in both groups and blood was taken for genetic analysis. Patients with RVH had a higher prevalence of left ventricular hypertrophy (LVH), carotid artery disease, and albuminuria than those with EH. In RVH, but not in EH, the DD genotype was significantly associated with severe arterial disease. In RVH, carotid disease (lumen narrowing >60%) was present in 62% of DD patients versus 25% of the other genotypes (OR = 4.90, 95% CI: 1.70-14.13). Such an association was also present in peripheral vascular disease: 72.4% in DD patients versus 41.6% in the other genotypes (OR = 3.67, 95% CI = 1.29-10.36). Logistic regression analysis showed that the DD genotype was the strongest predictor of risk of severe carotid disease. We conclude that, in atherosclerotic RVH, there is an association of the severity of vascular disease with the DD genotype of the ACE gene.

Risk factors for the progression of microalbuminuria in Japanese type 2 diabetic patients--a 10 year follow-up study

To clarify risk factors for the progression of microalbuminuria in Japanese type 2 diabetic patients, the longitudinal study for 10 years was conducted on 67 outpatients with type 2 diabetes, who had shown no overt proteinuria at baseline. The urinary albumin index (UAI) has been determined based on the mean of at least two random urine samples each year. Categories were defined as normoalbuminuria (UAI < 30.0 mg/g x Cr.), microalbuminuria (30.0 < or = UAI < 300.0), and macroalbuminuria (UAI > or = 300.0). Progression was defined as worsening of the category and/or more than doubling of the baseline UAI value. Multiple logistic regression analysis was performed using age, duration of diabetes, HbA1c, blood pressure, BMI, serum lipids, smoking habits, and alcohol consumption as independent variables and the progression of microalbuminuria as a dependent variable. Age and HbA1c were estimated as significant and independent variables. Furthermore, genetic polymorphisms of angiotensin I-converting enzyme (ACE) and angiotensinogen were analyzed to evaluate the genetic contribution. The D/D genotype of ACE was significantly more common in progressors than in non-progressors. These results suggest that glycemic control and age are important risk factors and the D/D genotype of ACE acts as a risk factor for the progression of microalbuminuria in Japanese type 2 diabetic patients.

Renal endosomes contain angiotensin peptides, converting enzyme, and AT(1A) receptors

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 (AT(1A)), 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 AT(1A) 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.

Kidney aminopeptidase A and hypertension, part I: spontaneously hypertensive rats

Tissue and plasma levels of aminopeptidase A (APA), the principal enzyme that hydrolyzes angiotensin II (Ang II) to angiotensin III, were measured in spontaneously hypertensive rats (SHR) and their normotensive control strain at 3 different ages corresponding to prehypertensive (4 weeks), developing (8 weeks), and established (16 weeks) phases of hypertension. Plasma APA activity was significantly but modestly elevated in SHR at all 3 ages compared with normotensive Wistar-Kyoto rats. Likewise, levels of APA in brain, heart, and adrenal gland were generally, but again only moderately, elevated in SHR at all ages. However, a large increase in APA activity was seen within the kidney in which APA levels were elevated 41%, 51%, and 68% in SHR at 4, 8, and 16 weeks of age, respectively. Kidney APA levels were also significantly increased in immunoblots from 8- and 16-week-old SHR. Glomeruli isolated from 16-week-old SHR had 57% higher APA activity and increased immunoreactivity compared with Wistar-Kyoto rats. To determine whether the increase in kidney APA activity in SHR was related to Ang II levels, SHR were treated for 2 weeks with the angiotensin-converting enzyme inhibitor captopril. Captopril treatment reduced blood pressure to normotensive values and resulted in a 25% reduction in kidney APA activity. These results suggest that APA expression in the kidney may be regulated by activity of the renin-angiotensin system. If so, this would further suggest that upregulation of APA during conditions in which Ang II levels were elevated would have a protective effect against Ang II-mediated cardiovascular diseases, whereas a decrease in APA expression or a failure to upregulate would exacerbate such conditions.

ACE Inhibitors and Renal Vascular Responses in the Spontaneously Hypertensive Rat

BACKGROUND: Substantial evidence has accumulated for the intrarenal generation of functionally important quantities of angiotensin II (Ang II). To assess the possibility that Ang II generation occurs beyond a barrier to diffusion from the vascular compartment, six angiotensin-converting enzyme (ACE) inhibitors varying widely in their lipid solubility were employed in the spontaneously hypertensive rat (SHR) and their normotensive controls (WKY). The biological end points were renal blood flow and its response to Ang II. RESULTS: Two ACE inhibitors, ramipril and captopril, induced a larger increase in renal blood flow and enhanced the renal vascular response to Ang II substantially more than did enalapril and lisinopril. The two prodrugs, enalapril and ramipril, which are substantially more lipophilic than the respective active drugs, enalaprilat and ramiprilat, showed equivalent responses. The partial agonist saralasin virtually abolished the renal vasodilator response to ramipril. The pattern of response was similar in WKY, but the responses were substantially smaller. CONCLUSIONS: The results support the concept that a functionally important compartment for intrarenal Ang II formation exists in the healthy rat and that this process is amplified in the SHR.

Association of the angiotensin I converting enzyme gene deletion polymorphism with early onset of ESRF in PKD1 adult polycystic kidney disease

To determine the effect of the ACE gene insertion/deletion (I/D) polymorphism, angiotensinogen gene M235T polymorphism and the angiotensin 1 receptor gene A1166C polymorphism on the age of onset of end-stage renal failure (ESRF) in PKD1 adult autosomal-dominant polycystic kidney disease (ADPKD), 189 individuals from 46 families with PKD1 were genotyped for each polymorphism. Of the 189 patients 52 (28%) reached ESRF at an average age of 48 +/- 1 year. In patients genotyped for the ACE gene insertion/deletion polymorphism the frequencies of the DD, ID and II genotypes were similar to those expected from Hardy Weinberg equilibrium. In patients with ESRF there was an excess of patients homozygous for the deletion allele (DD: 48% chi2 = 9.97 (1df) P = 0.002). Cumulative renal survival was significantly reduced among those with DD genotype compared to ID and II genotypes. The estimated mean renal survival (95% confidence intervals) were: DD, 52 years [48, 57]; II, 59 years [54, 63]; ID, 64 years [56, 72]; chi2 = 6.13 (1df) P = 0.013, DD versus ID/II. The mean age of renal failure was significantly younger in the DD genotype compared to ID and II genotypes (DD, ID, and II: 44 +/- 2, 49 +/- 2 and 54 +/- 3 years, respectively; P < 0.05 DD vs. ID, P < 0.05 DD vs. II). Ten of the eleven patients who reached ESRF before the age of 40 were homozygous for the deletion allele. The relative risk for ESRF below the age 40 for DD genotype was 17. For all ages there was an overall increased risk of 1.4 for ESRF with the DD genotype. There was no interaction between age of onset of ESRF and either the angiotensinogen M235T allele or angiotensin 1 receptor A1166C polymorphism. This study strongly suggests that PKD 1 patients homozygous for the deletion allele of the ACE gene are at increased risk of developing ESRF at a early age.

Expression of angiotensin converting enzyme and chymase in human atria

BACKGROUND

A cardiac angiotensin II-generating system has been suspected to be involved in various cardiac pathological conditions. Both angiotensin converting enzyme and human chymase can convert angiotensin I to angiotensin II.

OBJECTIVE

To clarify the relative contributions of these two enzymatic pathways to angiotensin II generation in vivo.

METHODS

We assessed the expression levels of messenger RNA (mRNA) for collagen type I alpha, transforming growth factor-beta(1), brain natriuretic peptide, angiotensin converting enzyme and chymase in right atrial appendages by competitive polymerase chain reaction and Northern blot analyses. Correlations among the concentrations of these mRNA were analysed to obtain insight that might be important in understanding the formation of angiotensin II in atrial tissue.

RESULTS

The collagen type I alpha and brain natriuretic peptide mRNA concentrations were correlated significantly to the mean pulmonary arterial pressure. Multivariate regression analysis revealed that the collagen type I alpha mRNA concentration could be explained in terms of the brain natriuretic peptide (P = 0.0005) and angiotensin converting enzyme (P = 0.0084) mRNA concentrations (r = 0.598, P < 0.0001). The chymase mRNA concentration had no significant correlation to the collagen type I alpha mRNA concentration. Moreover, multiple regression analysis revealed that the transforming growth factor-beta(1) mRNA concentration could be explained in terms of the angiotensin converting enzyme mRNA concentration alone (r = 0.424, P = 0.014).

CONCLUSIONS

The present results suggest that the level of angiotensin converting enzyme affects the tissue angiotensin II level in human atria; however, we could obtain no evidence that chymase is important in determining the tissue angiotensin II level.

Potential risk factors associated with progressive renal damage in childhood urological diseases: the role of angiotensin-converting enzyme gene polymorphism

PURPOSE

Experimental as well as human studies have established an important role for the renin-angiotensin system in the progressive deterioration of renal function. Recently genetic polymorphism in components of the renin-angiotensin system has been associated with several cardiovascular diseases, particularly variations in the angiotensin-converting enzyme gene that involve insertion (I) or deletion (D) of a 287 bp fragment. The D variant has been associated with myocardial infarction and cardiac hypertrophy.

MATERIALS AND METHODS

To assess whether this genetic variant is associated with worse prognosis in renal disorders we evaluated 70 children with congenital urological abnormalities, since a substantial number have progressive renal deterioration even after early corrective intervention. Renal deterioration was assessed by the presence or absence of radiographic evidence of parenchymal damage and serum creatinine.

RESULTS

Among patients with no radiographic renal parenchymal damage angiotensin-converting enzyme genotype distribution of II, ID and DD was 24, 67 and 9%, respectively. In contrast, a significantly different angiotensin-converting enzyme genotype distribution was observed in patients with evidence of parenchymal damage, that is 10, 49 and 41% for II, ID and DD, respectively (p < 0.05, chi-square 5.0). Mean serum creatinine plus or minus standard error in the former group was normal at 0.6 +/- 0.1 mg./dl., while in those with scarring it was elevated at 1.1 +/- 0.1 mg./dl., as expected. In patients with the DD genotype an overwhelming frequency of parenchymal damage was observed, that is of all 22 with that genotype 20 (91%) had parenchymal damage.

CONCLUSIONS

Considered together, these studies suggest that there are differences in the distribution of angiotensin-converting enzyme gene polymorphism in patients with congenital urological abnormalities who have evidence of renal parenchymal damage versus those who do not have such damage. Given that this genetic variation activates the renin-angiotensin system and this activation may be particularly robust in the kidney, we propose that the genotype of an individual independent of other factors modifies the likelihood of parenchymal loss in this setting.

Renal hemodynamic response to an angiotensin II antagonist, eprosartan, in healthy men

In view of the vasodilator potential of angiotensin-converting enzyme (ACE) inhibition via prostaglandins and kinins, we asked why renin inhibition induces a larger renal vasodilator response than ACE inhibitors in healthy humans in earlier studies. One possibility was that there was a more complete blockade of the renin system, which could also be achieved by an angiotensin II antagonist, eprosartan. We measured the hormonal and renal hemodynamic responses to eprosartan doses, from 10 to 400 mg in 9 healthy young men in balance on a 10-mmol/d sodium intake. The threshold eprosartan dose to influence renal perfusion was <10 mg, and the 100-mg dose induced a near-maximal vasodilator response of 135+/-19.7 mL x min(-1) x 1.73 m2. When the dose was increased to 400 mg, there was a modest additional increase of 147+/-57 mL x min(-1) x 1.73 m(-2). A highly significant dose-related fall in arterial blood pressure occurred (r=-.97; P<.001), with no indication of a maximal response at 400 mg. In 6 additional subjects, we compared responses to eprosartan on a high salt and a low salt diet. The renal response to 200 mg eprosartan on a high salt diet, 26.0+/-6.6 mL x min(-1) x 1.73 m(-2), was significantly less than that seen with the low salt diet (P<.001). There was no renal partial agonist angiotensin-like effect of eprosartan. Eprosartan reduced sharply the pressor, renal vascular, and hormonal responses to exogenous angiotensin II. The renal vasodilator response to the angiotensin II antagonist eprosartan closely resembles responses to renin inhibition and exceeds previously reported responses to ACE inhibitors. Thus, eprosartan probably exerted its effect via the angiotensin receptor. More complete blockade of the renin system can be achieved by pharmacological interruption at this level, a finding that could have therapeutic implications.

Renal tissue angiotensins during converting enzyme inhibition in the spontaneously hypertensive rat

To compare the effects of an angiotensin-converting enzyme inhibitor on circulating and tissue renin-angiotensin system (RAS), we measured different RAS parameters during the first day of treatment (Day1) as well as after two weeks of treatment (Day14). Ramipril was given orally once daily to adult male spontaneously hypertensive rats (SHR). Renin activity (RA), angiotensin converting enzyme (ACE) activity and levels of angiotensin I (ang I) and angiotensin II (ang II) in the plasma, renal cortex and renal medulla were assessed at Day1 and Day14 of the treatment. In the plasma, both RA and ang I increased 10 to 15 fold one to four hours after acute as well as at Day14 of ramipril treatment and then returned to basal values within 24 hours. Plasma ang II levels were not significantly decreased at Day1 or Day14. The decrease in the ang II/ang I ratio suggested a sustained inhibition of plasma ACE at Day14. In the renal cortex and medulla, a clearly different pattern was observed: in ramipril treated rats, RA in the renal cortex and medulla did not change at Day1 but at Day14 we observed a slight and sustained increase in RA. Despite very high basal levels of RA, ang I levels in the renal cortex were comparable to those in the plasma. The ang I level increased only one-fold one hour after ramipril intake at Day1 and Day14. This suggests that angiotensinogen may have a limiting role in the synthesis of ang I in the kidney. Ang II levels were slightly higher in the renal cortex and medulla than in the plasma suggesting local synthesis of the peptide. In the kidney, ang II levels decreased one and four hours after the acute or prolonged ramipril treatment and the ang II/ang I ratio was reduced at the same time. Our results show that the responses of the plasma and kidney components of the RAS to ACE inhibition are different in the plasma and the kidney suggesting that the circulating and tissue RAS are at least in part independent.

Tissue renin-angiotensin system: a site of drug action?

In this review, we present background material that provides partial support for a tissue renin-angiotensin system (RAS). Evidence for the existence of this system relied in part on the use of drugs, which has entailed using low doses or concentrations of angiotensin-converting enzyme inhibitors, renin inhibitors, and angiotensin antagonists to block the RAS in vascular beds and in isolated arteries or organs. Other evidence for a tissue RAS has depended upon measurements of the components of the system, i.e. enzymes, substrates, and mRNAs for these proteins. All of these components were first believed to be present in the heart and blood vessels; however, it is now known that renin in the circulating blood derived from the kidney is used for the local synthesis of angiotensins. The main emphasis of the review is on the renal RAS because it is believed that the local RAS is most prominent in this organ. The renal RAS is probably involved in the long-rather than short-term regulation of renal vascular resistance and maintenance of normal blood pressure through the regulation of sodium reabsorption.

Biological functions of angiotensin and its receptors

Angiotensin receptors are present in a number of organs and systems including heart, kidney, gonad, and placenta; pituitary and adrenal glands; the peripheral vessels, and the central nervous system. This octapeptide exerts diverse effects that include induction of cell hypertrophy and/or hyperplasia and a stimulation of hormone synthesis and ion transport in the heart, kidney, and adrenal, primarily through type 1 (AT1) receptors. In the kidney, several heterogeneous cell populations--endothelial, epithelial, and vascular--carry AT1 receptors. Some studies suggest that AT2 receptors are also functional, but the cell type carrying this receptor and the nature of its specific function have not been fully elucidated. Although studies indicate that AT1 receptors are affected in response to physiological and pathophysiological manipulations, the functional significance of these modulations remains largely uncertain. Nevertheless, recent human genetic studies indicate that polymorphisms in AT1 receptors, as well as in other angiotensin-related genes, have significant impact on organ remodeling processes of the heart and the kidney.

The urinary bladder angiotensin system: response to infusions of angiotensin I and angiotensin-converting enzyme inhibitors

The circulating and urinary bladder tissue concentrations of angiotensin I (ANG I) and angiotensin II [ANG-(1-8)] were examined in anesthetized Sprague-Dawley male rats given an intravenous bolus infusion of either ANG I, the angiotensin-converting enzyme (ACE) inhibitors enalaprilat or ramiprilat, or saline. The mean concentrations of ANG I and ANG-(1-8) were markedly higher in the urinary bladder tissue than in whole blood. There was a significant increase in the concentration of ANG I and ANG-(1-8), both in the urinary bladder tissue and the circulation, after the ANG I infusion. Both ACE inhibitors were associated with an increase in the concentration of whole blood ANG I; however, tissue ANG I levels were significantly increased only following ACE inhibition with ramiprilat but not with enalaprilat. Both plasma and urinary bladder tissue ANG-(1-8) levels decreased significantly following ACE inhibition, but only with ramiprilat. The elevated urinary bladder tissue levels of ANG I and ANG-(1-8) at baseline, compared with circulating levels, and the maintenance of ANG-(1-8) in bladder tissue in the face of inhibition of the circulatory renin-angiotensin system with enalaprilat support the presence of an autocrine/paracrine renin-angiotensin system in the urinary bladder. Under the current experimental conditions, ramiprilat appears to have enhanced bladder activity compared with enalaprilat.

Angiotensin II in the evolution of experimental heart failure

Although angiotensin II (Ang II) has been implicated in the pathophysiology of congestive heart failure, its temporal and regional changes during the development and progression of the disease are poorly defined. Our objective was to assess circulating, renal, cardiac, and vascular Ang II in a canine model of rapid ventricular pacing-induced heart failure that evolves from early left ventricular dysfunction to overt congestive heart failure. Ang II was measured by radioimmunoassay with low cross-reactivity to other angiotensins. Control, early left ventricular dysfunction, and overt congestive heart failure dogs were studied. Early left ventricular dysfunction was characterized by impaired cardiac function, cardiac enlargement, preserved renal perfusion pressure, maintained urinary sodium excretion, and normal plasma renin activity. Overt congestive heart failure was characterized by further impaired cardiac function and cardiac enlargement, reduced renal perfusion pressure, urinary sodium retention, and increased plasma renin activity and plasma Ang II. In early left ventricular dysfunction dogs, renal cortical, renal medullary, ventricular, and aortic Ang II were unchanged, and atrial Ang II was decreased. In overt congestive heart failure dogs, Ang II was increased in the kidney and heart compared with normal dogs and in all tissues compared with early left ventricular dysfunction dogs. The greatest increase in tissue Ang II occurred in the renal medulla. We conclude that early increases in local renal, myocardial, and vascular Ang II do not occur in this model of early left ventricular dysfunction and may even be suppressed. In contrast, increased myocardial and particularly renal Ang II in association with increased circulating Ang II are hallmarks of overt experimental congestive heart failure. These studies provide new insights into the temporal and regional alterations in Ang II during the progression of experimental congestive heart failure.

Therapeutic, but not low-dose, angiotensin-converting enzyme inhibition causes regression of cardiovascular changes in spontaneously hypertensive rats

Therapy with angiotensin II-converting enzyme (ACE) inhibitors has been suggested to prevent cardiovascular hypertrophy in hypertension even in doses that are subantihypertensive. We investigated the effects of two different ACE inhibitors on blood pressure and cardiovascular changes during as well as after discontinuation of treatment in spontaneously hypertensive rats (SHR). SHR were treated with either enalapril (ENA) or ramipril (RAM) from age 12 to age 20 weeks. Each drug was given in either an antihypertensive (ENA 15 mg center dot kg-1, RAM 3 mg center dot kg-1) or a subantihypertensive (ENA 50 mu g center dot kg-1, RAM 10 mu g center dot kg-1) dose. Mean arterial pressure (MAP) was reduced with antihypertensive doses of ENA (26%) as well as RAM (21%). Regression of cardiovascular changes occurred as reduction in left ventricular (LV) weight/body weight ratio (25 and 21% for ENA and RAM, respectively), reduction in perfusion pressure at maximal vasodilation of the perfused hindquarter (PPdil, 17 and 17%), and reduction in maximal developed pressure (PPmax, 13 and 17%). These effects partly persisted 10 weeks after treatment was discontinued. However, treatment with subantihypertensive doses of ENA and RAM had no effect on MAP, LV/body weight ratio, PPdil, or PPmax. Overall, regression of cardiovascular parameters correlated closely to the decrease in MAP. Similarly, no changes in MAP, LV weight/body weight ratio, PPdil, or PPmax were noted when young SHR were treated with subantihypertensive doses of RAM from age 6 to age 12 weeks, during which time hypertension becomes established. At doses having equal effects on blood pressure, plasma concentrations of RAM were considerably lower than those of ENA. Skeletal muscle concentrations were very low or undetectable in comparison to plasma concentrations for both drugs. Therefore, both RAM and ENA caused regression of cardiovascular changes that could be explained by a concomitant reduction in blood pressure. This regression persisted for a considerable time after discontinuation of treatment. On the other hand, no specific antitrophic effects in the absence of blood pressure reduction was evident with either drug. Furthermore, despite substantial differences in plasma concentrations, RAM, and ENA administered chronically appeared to affect cardiovascular parameters equally in the adult SHR.

Angiotensin converting enzyme gene polymorphism: potential silencer motif and impact on progression in IgA nephropathy

Since the renin angiotensin system (RAS) is established as an important factor in renal disease progression, we determined whether RAS alleles that have been linked to variability in outcome in several cardiovascular diseases also affect progression of IgA nephropathy. These genetic variants include: (1) angiotensin I converting enzyme deletion polymorphism in intron 16 (ACE I/D), reported to be associated with increased risk of myocardial infarction as well as left ventricular hypertrophy; (2) a point mutation in the angiotensinogen (Agt) gene resulting in a methionine to threonine substitution at residue 235 (M235T), reported to be associated with hypertension in Caucasians; and (3) an angiotensin receptor type I (ATR) A to C transition at bp 1166 (A1166C) which shows synergy with the deleterious effects of the ACE DD genotype in myocardial infarction. We examined these polymorphisms by PCR amplification of genomic DNA samples from 64 Caucasian patients in the USA (age 6 to 83 years) with biopsy-proven IgA nephropathy whose renal status was followed for an average of almost seven years. Patients who presented with and maintained normal serum creatinine (Cr, < 1.5 mg/dl), had ACE genotype frequencies of II:35%, ID:61%, DD:4%. By contrast, in patients with progression (initially normal Cr increased to a mean of 4.5 +/- 0.86 mg/dl), ACE genotype frequencies were II:22%, ID:44%, DD:33% (P = 0.057 by Fishers's exact test, vs. non-progressors). The association of the DD genotype with progression was even more striking when patients with other risk factors (hypertension and/or heavy proteinuria) were excluded. In this subgroup, the genotype frequencies in patients with stable creatinine versus those with deterioration in renal function was 53%, 47%, and 0% versus 0%, 40%, and 60%, respectively, for II, ID, and DD genotypes (P = 0.009 by Fisher's exact test, progressors vs. non-progressors). Further, sequence analysis of the I gene polymorphism revealed a potential 13 bp silence motif. Neither the Agt 235T nor the ATR A 1166C gene variants, however, was associated with deterioration of renal function. Taken together, these results indicate that, although polymorphism in each of the three genes in the RAS system has been linked to cardiovascular diseases, only the ACE I/D polymorphism is associated with progressive deterioration in renal function in IgA nephropathy. Since previous observations link ACE polymorphism with ACE activity, these findings imply a widespread importance of ACE in modulating destructive processes in different organs.

Angiotensin II-modified LDL is taken up by macrophages via the scavenger receptor, leading to cellular cholesterol accumulation

The incidence of myocardial infarction is significantly higher in hypertensive patients with increased plasma concentration of angiotensin (Ang) II. Ang II was shown to bind to LDL in vitro, and in the present study we showed its binding to LDL in vivo. Ang II (10(-7) mol/L) was incubated with LDL for 3 hours at 37 degrees C, followed by reseparation of the modified lipoprotein (Ang II-LDL) and its incubation with J-774 A.1 macrophages. Binding of Ang II to LDL significantly increased the lipoprotein protein degradation (by 25%) and its cell association (by 75%) compared with nontreated LDL. Unlike Ang II-LDL, both Ang I-LDL and Ang III-LDL were taken up by macrophages similar to native LDL. The lipid composition and size of Ang II-LDL were similar to those of native LDL, and it was not aggregated. Ang II-LDL was not oxidized, as the contents of malondialdehyde and peroxides were not different from those found in native LDL. On heparin-Sepharose column chromatography, Ang II-LDL was eluted in the void volume, like acetylated LDL (Ac-LDL) and unlike native LDL, which binds to heparin. The cellular degradation of Ang II-125I-labeled LDL by J-774 A.1 macrophages of Ang II-125I-labeled LDL by J-774 A.1 macrophages was studied in the presence of a 50-fold excess of nonlabeled native LDL, Ang II-LDL, Ac-LDL, or oxidized LDL (Ox-LDL). Whereas native LDL had no effect on the degradation of Ang II-125I-LDL by the macrophages, Ac-LDL, Ox-LDL, and Ang II-LDL reduced the cellular uptake of the lipoprotein by 77%, 82%, and 87%, respectively. Similarly, fucoidin but not free Ang II reduced macrophage degradation of the labeled Ang II-LDL. We conclude that Ang II can modify LDL to a form that is not oxidized or aggregated but is still taken up at an enhanced rate by macrophages via the scavenger receptor.

Effects of ACE inhibitors on circulating versus cardiac angiotensin II in volume overload-induced cardiac hypertrophy in rats

BACKGROUND

Cardiac volume overload by an aortocaval shunt increases left ventricular end-diastolic pressure (LVEDP) and plasma and cardiac renin activity and results in LV hypertrophy. To a similar extent, the angiotensin-converting enzyme (ACE) inhibitors enalapril and quinapril prevent the increase in LVEDP. However, only quinapril attenuates the development of LV hypertrophy. We hypothesize that a low affinity of enalapril for cardiac ACE results in continuing generation of cardiac angiotensin II and thus hypertrophic growth of cardiomyocytes.

METHODS AND RESULTS

In the present study, we assessed plasma and cardiac angiotensins I and II 1 and 7 days after aortocaval shunt and the effects of enalapril and quinapril started 3 days before surgery on plasma and cardiac angiotensin I and II at the same time points. Aortocaval shunt increased plasma angiotensin II at 1 day by 180%, but only a small increase (by 40%) persisted at 7 days. Aortocaval shunt increased LV angiotensin II by 100% and 65% at 1 and 7 days, respectively. Both blockers similarly prevented the increase in plasma angiotensin II by aortocaval shunt at both time points. In contrast, only quinapril prevented the rise in LV angiotensin II induced by shunt at 1 and 7 days.

CONCLUSIONS

Aortocaval shunt increases LVEDP and plasma and cardiac angiotensin II and results in LV hypertrophy. Only prevention of the increase in LVEDP and in plasma and cardiac angiotensin II attenuates the development of LV hypertrophy, consistent with the concept that angiotensin II is involved in the development of cardiac hypertrophy by aortocaval shunt by both hemodynamic and cardiac trophic effects. This study is the first to show that differences in affinity for cardiac ACE may determine the effect of ACE inhibitors on cardiac angiotensin II and therefore cardiac hypertrophy.

Cardiac renin-angiotensin system in the hypertrophied heart

BACKGROUND

The cardiac renin-angiotensin system (RAS) has been suggested to play an important role in heart failure and cardiac hypertrophy. In the present study, we evaluated the expression of each component of the RAS in hypertrophied heart induced by aortocaval shunt.

METHODS AND RESULTS

The expression levels of renin, angiotensinogen, angiotensin-converting enzyme (ACE), and angiotensin II type Ia and Ib receptor (AT1aR and AT1bR) mRNA were determined by the reverse transcription-polymerase chain reaction method owing to the relatively low expression levels of these mRNAs in the ventricle. The expression level of renin or angiotensinogen mRNA in the ventricle was very low, more than 1000-fold lower than that in the kidney or liver, respectively. The expression of ACE mRNA in the ventricle was relatively abundant and was increased in the hypertrophied ventricle in this model, whereas no significant increases in the expression levels of AT1aR and AT1bR mRNA were observed. Administration of lisinopril attenuated the development of left and right ventricular hypertrophy in this model and was accompanied by an attenuation of the upregulation of the ACE, collagen type I-alpha, and vimentin mRNAs. Because the activity of the circulating RAS in the aortocaval shunt rats was not higher than that in the sham-operated rats, the effects of lisinopril in attenuating the ventricular hypertrophy may be due to inhibition of the increased ACE in the ventricle.

CONCLUSIONS

The present study supports the importance of ACE expressed in the ventricle in the development of hypertrophy induced by aortocaval shunt.

Renal circulation and blockade of the renin-angiotensin system. Is angiotensin-converting enzyme inhibition the last word?

The mechanism by which angiotensin-converting enzyme (ACE) inhibition influences renal perfusion and function has assumed growing importance as alternatives for blocking the system have emerged. Neither renin inhibitors nor angiotensin II (Ang II) antagonists are likely to trigger responses similar to ACE inhibitor-induced involvement of kinins, prostaglandins, or nitric oxide. Several observations suggest species variation in the contribution of these pathways to the renal response to ACE inhibition. In humans, recent investigation suggests that virtually all of the renal response is due to a fall in Ang II formation. Perhaps most persuasive is the surprising observation that the renal hemodynamic response to renin inhibitors exceeds by more than 50% the response to ACE inhibition in healthy humans. To the extent that kinins or prostaglandins contribute to the renal response to ACE inhibition, one would anticipate a smaller response to renin inhibition. Possible explanations include an unanticipated additional action of renin inhibitors, better tissue penetration of these highly lipophilic agents, or more effective blockade of Ang II formation through an action at the rate-limiting step or non-ACE-dependent Ang II generation. Substantial evidence favors the latter two possibilities. Whatever the explanation, these observations raise the intriguing possibility that the undoubted therapeutic efficacy of ACE inhibition in renal injury, documented most rigorously for type I diabetes mellitus, might be exceeded with the newer classes of agent.

Effect of captopril and angiotensin II receptor blockade on pressure natriuresis in transgenic TGR(mRen-2)27 rats

The pressure-natriuresis curve of transgenic rats harboring an extra mouse renin gene [TGR(mRen-2)27] is shifted rightward compared with controls; however, whether intrarenal angiotensin II effects are responsible for the rightward shift is unknown. To clarify this issue we infused the converting enzyme inhibitor captopril or the angiotensin II receptor blocker CV 11974 into transgenic and normotensive Sprague-Dawley Hannover control rats. We eliminated any other neural or endocrine regulatory differences between transgenic and control rats by renal denervation and infusion of vasopressin, aldosterone, corticosterone, and norepinephrine in sufficient quantities to occupy all receptors. Sodium excretion increased from 3.4 +/- 1.2 to 10.1 +/- 0.5 mumol/min per gram kidney weight in transgenic rats when renal perfusion pressure was increased from 158 to 201 mm Hg. Captopril (4 mg/kg) and CV 11974 (0.1 mg/kg) shifted the pressure-natriuresis curve of transgenic rats leftward, so that sodium excretion was threefold higher at similar renal perfusion pressures (150 to 160 mm Hg). Similarly, fractional sodium and water excretion curves were shifted leftward, so that values for transgenic and control rats were no longer different. Over the pressure range, renal blood flow in transgenic rats ranged from 3.1 +/- 0.7 to 4.4 +/- 0.5 mL/min per gram kidney weight and increased (P < .05) with both captopril and CV 11974 to ranges from 4.8 +/- 0.9 to 6.8 +/- 0.6 or from 4.5 +/- 0.7 to 6.9 +/- 1.0 mL/min per gram kidney weight, respectively. Glomerular filtration rate in transgenic rats, on the other hand, was not increased. Transgenic kidneys showed severe hypertension-induced nephrosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)