Plasma Angiotensin-converting Enzyme Activity Research Articles

Differential ACE expression among tissues in allele-specific Wistar rat lines

In humans, the insertion/deletion polymorphism in the angiotensin converting enzyme (ACE) gene accounts for half of the variance in plasma ACE activity. The deletion allele is associated with high plasma ACE activity, cardiovascular disease, and renal disease. In rat, a similar association is found between the B and L alleles of a microsatellite marker in the ACE gene. We identified the B/L variation in the Wistar outbred rat and bred two lines homozygous for the two alleles (WU-B and WU-L). ACE activity was measured in serum, heart, kidney, and aorta homogenates. Immunohistochemistry and ACE mRNA expression were performed in heart, kidney, and aortic tissue. Aortic rings were collected and stimulated with AngI, AngII, and AngI with Lisinopril to measure ACE functional activity by vasoconstrictor response. Serum, heart, and kidney ACE activity and kidney mRNA expression were two-fold higher in WU-B. Kidney staining showed a clear difference in tubular ACE expression, with more staining in WU-B. While in aorta ACE activity and mRNA expression was twofold higher in WU-L, functional conversion of AngI was higher in WU-B, indicating either a functional difference in AngI to AngII conversion between the two alleles due to different splicing or the presence of other factors involved in the conversion that are differentially expressed as the result of differences in the ACE alleles. The newly developed WU-B and WU-L lines show tissue-specific differences in ACE expression and activity. This provides an experimental tool to study the pathophysiologic consequences of differences in ACE alleles in renal and cardiovascular disease.

Isoflavone genistein inhibits the angiotensin-converting enzyme and alters the vascular responses to angiotensin I and bradykinin

Genistein produces antihypertensive and beneficial cardiovascular effects, although the mechanisms for these effects are not known. We examined whether genistein inhibits the in vivo responses to angiotensin I or enhances the responses to bradykinin in anaesthetized rats as a result of angiotensin-converting enzyme inhibition. We have also studied the in vitro effects produced by genistein on the angiotensin-converting enzyme activity. We measured the changes in systemic arterial pressure induced by angiotensin I in doses of 0.03 to 10 µg/kg, by angiotensin II in doses of 0.01 to 3 µg/kg, and to bradykinin in doses of 0.03 to 10 µg/kg in anaesthetized rats pretreated with vehicle (controls), or a single i.v. dose of genistein 25 mg/kg, or daily genistein 25 mg/kg i.v for two days, or a single i.v. dose of captopril 2 mg/kg. Plasma angiotensin-converting enzyme activity was determined in controls and genistein-treated rats using a fluorometric method. The effects of genistein (3–300 µmol/l) on in vitro angiotensin-converting enzyme activity were assessed by adding genistein to plasma samples and measuring angiotensin-converting enzyme activity. We found significant lower angiotensin-converting enzyme activity in plasma samples from rats pretreated with genistein compared with those found in the Control group (77.7 ± 8.1 his-leu nmol/min/ml and 108.7 ± 8.4 his-leu nmol/min/ml, respectively; P = 0.01). The incubation of genistein with plasma samples showed that genistein decreased the angiotensin-converting enzyme activity in plasma in a concentration-dependent manner ( P < 0.01). These findings indicate that genistein inhibits the angiotensin-converting enzyme in vivo and in vitro and may explain, at least in part, the antihypertensive and beneficial vascular effects produced by genistein.

High plasmatic angiotensin‐converting enzyme (ACE) activity is not correlated with training‐induced left ventricular growth in ACE congenic rats

The aim of this study was to determine the influence of angiotensin-converting enzyme (ACE) genotype on left ventricular growth after endurance training, in ACE congenic rats with plasma ACE activity twice as high as the donor strain (LOU), thus mimicking the ACE I/D polymorphism observed in humans. LOU and congenic rats (n = 12) were submitted to an endurance training on a treadmill for 7 weeks, while similar LOU and congenic rats (n = 10) constituted the control groups. Blood pressure, skeletal muscle citrate synthase activity, plasma and left ventricular ACE activity were assessed, and echocardiography was performed before and after the training. Angiotensin-converting enzyme plasmatic activity of congenic rats (188.2 +/- 26.6 in controls and 187.1 +/- 22.6 IU in trained rats respectively) was twofold that of the LOU strain (91.9 +/- 23.3 in controls, and 88.3 +/- 18.1 IU in trained rats respectively). After training, congenic and LOU rats showed a similar significant increase in citrate synthase activity (P < 0.05), and in the left ventricular mass/body mass ratio x 10(3): 3.7 +/- 0.3 and 3.6 +/- 0.6 in the trained congenic and LOU groups, respectively, vs. 3.0 +/- 0.1 and 2.9 +/- 0.2 in the control congenic and LOU groups respectively (P < 0.05). There was no significant correlation between ACE plasma activity and left ventricular mass in trained or untrained congenic rats. We conclude that training-induced left ventricular growth is not associated with plasma ACE activity in congenic rats.

Pharmacokinetics and pharmacodynamics of ramipril and ramiprilat in healthy cats

The pharmacokinetics of ramipril and its active metabolite, ramiprilat, was determined in cats following single and repeated oral doses of ramipril (Vasotop tablets) (once daily for 9 days) at dose rates of 0.125, 0.25, 0.5 and 1.0 mg/kg. The pharmacodynamic effects were assessed by measuring plasma angiotensin-converting enzyme (ACE) activity. Maximum ramipril concentrations were attained within 30 min following a single dose and declined rapidly (concentrations were below the limit of quantification 4 h after treatment). Peak ramiprilat concentrations were detected at approximately 1.5 h. The apparent terminal half-life (t((1/2)beta)) was > or =20 h irrespective of the dose. Ramiprilat accumulated in plasma (ratio of accumulation 1.3 to 1.9 depending on the dose rate) following repeated administration. Steady-state conditions were attained after the second dose. Excretion was predominant in faeces (87%) and to a lesser extent in urine (11%). The rate and extent of absorption of ramipril as well as its conversion to ramiprilat were not significantly influenced by the presence of food in the gastrointestinal tract. Plasma-ACE activity was almost completely abolished 0.5-2.0 h after treatment, irrespective of the dose rate. Significant inhibition of ACE activity of 54.7 to 82.6% (depending on the dosage) was still present 24 h after treatment. Treatment was well-tolerated in all cats. Ramipril at a dose rate of 0.125 mg/kg once daily produces significant and long-lasting inhibition of ACE activity in healthy cats. The appropriateness of this dosage regime needs to be confirmed in diseased cats.

The association of ACE gene D/I polymorphism with cardiovascular risk factors in a population from Rio de Janeiro

Our aim was to determine the frequencies of the angiotensin-converting enzyme (ACE) gene alleles D and I and any associations to cardiovascular risk factors in a population sample from Rio de Janeiro, Brazil. Eighty-four adults were selected consecutively during a 6-month period from a cohort subgroup of a previous large cross-sectional survey in Rio de Janeiro. Anthropometric data and blood pressure measurements, echocardiogram, albuminuria, glycemia, lipid profile, and ACE genotype and serum enzyme activity were determined. The frequency of the ACE*D and I alleles in the population under study, determined by PCR, was 0.59 and 0.41, respectively, and the frequencies of the DD, DI, and II genotypes were 0.33, 0.51, and 0.16, respectively. No association between hypertension and genotype was detected using the Kruskal-Wallis method. Mean plasma ACE activity (U/mL) in the DD (N = 28), DI (N = 45) and II (N = 13) groups was 43 (in males) and 52 (in females), 37 and 39, and 22 and 27, respectively; mean microalbuminuria (mg/dL) was 1.41 and 1.6, 0.85 and 0.9, and 0.6 and 0.63, respectively; mean HDL cholesterol (mg/dL) was 40 and 43, 37 and 45, and 41 and 49, respectively, and mean glucose (mg/dL) was 93 and 108, 107 and 98, and 85 and 124, respectively. A high level of ACE activity and albuminuria, and a low level of HDL cholesterol and glucose, were found to be associated with the DD genotype. Finally, the II genotype was found to be associated with variables related to glucose intolerance.

Soy protein hydrolysate ameliorates cardiovascular remodeling in rats with l-NAME-induced hypertension

Pepsin-digested soy protein hydrolysate has been reported to be responsible for many of the physiological benefits associated with soy protein consumption. In the present study, we investigated the effects of soy protein hydrolysate with angiotensin-converting enzyme (ACE) inhibitory potential on the blood pressure and cardiovascular remodeling in rats with N ω-nitro- l-arginine methyl ester hydrochloride ( l-NAME)-induced hypertension. Rats were fed a diet containing l-NAME (50 mg/kg body weight) with or without soy protein hydrolysate (1%, 3% or 5%) for 6 weeks. We found that ingestion of soy protein hydrolysate retarded the development of hypertension during the 6-week experimental period without affecting the amount of food intake. Although there was no difference in plasma ACE activity or tissue nitric oxide levels, ACE activity in the heart of rats consuming soy protein hydrolysate was significantly lower than that of the control group. Moreover, cardiac malonaldehyde and tumor necrosis factor-α concentrations were also lower in the soy protein hydrolysate group. No difference in plasminogen activator inhibitor-1 level was found in plasma or cardiovascular tissue. In the histopathological analysis, we also found that soy protein hydrolysate ameliorated inflammation and left ventricle hypertrophy in the heart. These findings suggest that soy protein hydrolysate might not only improve the balance between circulating nitric oxide and renin–angiotensin system but also show beneficial effects on cardiovascular tissue through its ACE inhibitory activity.

Inhibitory profiles of captopril on matrix metalloproteinase-9 activity

To investigate the inhibitory profiles of angiotensin-converting enzyme (ACE) inhibitors on matrix metalloproteinase-9 (MMP-9) activity, the inhibitory activity and molecular interaction of captopril on human MMP-9 were studied. Plasma MMP-9 and ACE activities in samples from patient with acute myocardial infarction were similarly inhibited by captopril. Molecular models showed that captopril directly bound to the MMP-9 active center. Compared with the other ACE inhibitors, the compact structure of captopril seemed to make the inhibitory profiles on the MMP-9 active site.

A Twofold Genetic Increase of ACE Expression Has No Effect on the Development of Spontaneous Hypertension

To study the regulation of a naturally occurring genetic variant of high angiotensin-converting enzyme (ACE) gene (Ace in rat) expression, i.e., the Ace allele of the normotensive Wistar-Kyoto (WKY) rat, in the hypertensive background of stroke-prone spontaneously hypertensive (SHRSP) rats. We analyzed a congenic strain termed SHRSP.WKY-Ace derived from SHRSP in which a chromosomal fragment of rat chromosome 10 including Ace was replaced by the WKY locus. We compared blood pressures by radiotelemetry, measured plasma ACE activity, tissue ACE messenger RNA (mRNA) and enzyme activities in lung, kidney, and left ventricle (LV) of the heart in adult animals. Congenic animals demonstrated a twofold increase in plasma ACE activity in comparison to SHRSP (P < 0.05) and thus similar levels to WKY. The increased tissue expression of ACE mRNA and enzyme activities in lung, kidney, and LV observed in WKY were similarly found in congenic animals when compared to SHRSP (P < 0.05, respectively). Systolic and diastolic blood pressures were not different between congenic and SHRSP animals. Analysis of renin in plasma and angiotensin peptides in LV tissues indicated the induction of compensatory mechanisms by downregulation of renin and angiotensin I (Ang I) concentrations in congenic animals. We demonstrated that genetically determined high ACE expression linked to WKY Ace remains unchanged in the hypertensive background of SHRSP.WKY-Ace. Our data indicate that buffering mechanisms in the renin-angiotensin system contribute to the finding that the development of spontaneous hypertension is not affected, despite an average twofold higher expression of ACE in congenic animals.

Effects of Soy Protein Hydrolysate on Blood Pressure and Angiotensin-Converting Enzyme Activity in Rats with Chronic Renal Failure

We investigated the effects of soy protein and soy protein hydrolysate on blood pressure control, angiotensin-converting enzyme (ACE) activity, and renal function in a rat chronic renal failure model. Rats that had undergone a 5/6 nephrectomy were separated into three groups and fed different experimental diets for 14 weeks. At the end of the study, rats that fed a diet containing soy protein as the protein source had better blood pressure control and renal function, as well as lower circulating ACE activity and renal tumor-necrosis factor-alpha (TNF-alpha) concentration than rats fed a casein protein diet. Soy protein hydrolysate was shown to be as effective as soy protein in preventing the elevation of blood pressure, the progression of renal failure, and decreases in kidney TNF-alpha level, plasma ACE activity, and insulin concentration. In conclusion, the beneficial effects of consuming soy protein on blood pressure and renal function may be mediated mostly by its pepsin-digested hydrolysate through its ACE inhibitory activity.

Cardiovascular effect of Artemisia herba alba aqueous extract in spontaneously hypertensive rats

This study aimed to evaluate the hypotensive activity of Artemisia herba alba aqueous extract (AHAE) in spontaneously hypertensive rats (SHR). AHAE was lyophilized and administered daily at a dose of 150 mg/kg for 20 days. AHAE administration produced a significant reduction in systolic blood pressure after 8 days of oral administration (P < 0.01), and a sustained reduction was observed at the end of treatment (P < 0.01). Heart rate remained unchanged during the 20 days of oral AHAE administration. In addition, AHAE administration produced a significant increase in urinary output (P < 0.01) and glomerular filtration rate (P < 0.01) on day 8 of treatment. Urinary electrolyte excretion was also modified during the 20 days of AHAE administration, and a significant increase in urinary sodium and potassium excretion was observed from day 4 (P < 0.01) to day 20 (P < 0.001). However, urinary chloride excretion was increased from day 8 (P < 0.01) to the end of treatment (P < 0.001). The hypotensive effect appeared to be independent of the renin-angiotensin system since AHAE did not affect plasma angiotensin-converting enzyme or renin activities (P > 0.05) after 20 days of oral administration. We conclude that AHAE possesses antihypertensive activity in SHR and that the underlying mechanism appears to involve, at least in part, an increase in urine and electrolyte output.

Is the influence of variation in the ACE gene on the prospective risk of Type 2 diabetes in middle-aged men modified by obesity?

There is strong evidence for the presence of a functional renin-angiotensin system in diabetogenic tissues, and ACE (angiotensin-converting enzyme) inhibitors may improve glucose metabolism in those individuals at high risk of developing T2DM (Type 2 diabetes). In the present study, we tested the hypothesis that subjects with genetically lower plasma and tissue ACE activity, because of their ACE [I/D (insertion/deletion)] genotype, would have a lower risk of T2DM in 2642 healthy middle-aged Caucasian men (mean age, 56 years) followed-up for 15 years. Obesity was the strongest predictor of T2DM, with an HR (95% CI) [hazard ratio (95% confidence interval)] of 3.74 (2.66-5.26) (P<0.0001). Overall there was no association between ACE genotype (II homozygotes, n=623; and D allele carriers, n=2019) and risk of T2DM, and although in lean men there was no genotype difference in risk in D allele carriers compared with II homozygotes [adjusted HR=0.75 (95% CI, 0.46-1.22)], in obese (body mass index >30 kg/m(2)) men the risk of T2DM was higher [adjusted HR=4.26 (95% CI, 1.30-13.93)] with a genotype-obesity interaction of P=0.01. A similar pattern of risk was seen by re-analysis of a previously published case-control study, where D allele carriers had a non-significant 1.30 (0.97-1.74)-fold higher risk of developing T2DM than II homozygotes when non-obese, but a 1.79 (1.17-2.72) (P=0.007)-fold higher risk when obese. Further prospective studies are needed to confirm these findings. The ACE D allele may worsen glucose metabolism, which could raise the prospective T2DM risk in obese men, but not in lean men. In obesity, adipose tissue undergoes inflammatory infiltration and the subsequent higher levels of pro-inflammatory angiotensin II may explain this association.

CHRONIC SALT LOADING AND CARDIOVASCULAR‐ASSOCIATED CHANGES IN EXPERIMENTAL DIABETES IN RATS

1. High-sodium intake may increase blood pressure and diabetes is a salt-sensitive condition. In the present study, we evaluated cardiovascular changes and their neurohumoral mechanisms in streptozotocin (STZ)-diabetic rats that underwent chronic salt loading. 2. We studied male Wistar rats (150-280 g) 14 days after the injection of either STZ (50 mg/kg, i.v.; D; n = 18) or citrate buffer (C; n = 16). After the induction of diabetes, animals were maintained for 14 days with free access to standard rat chow and tap water (C and D groups) or 1% NaCl solution (C-S and D-S groups). We conducted two experiments. Experiment 1 consisted of basal arterial pressure (AP) measurement (30 min) followed by the evaluation of AP responsiveness to phenylephrine and sodium nitroprusside. One day later, with the rats anaesthetized, a blood sample was collected to test for glycaemia, plasma angiotensin-converting enzyme (ACE) activity and renin. Kidneys were removed for the determination of tissue ACE activity. Experiment 2 comprised 24 h urine collection followed by 3 days of cardiovascular records, which consisted of a 30 min basal AP measurement, followed by injection of blockers of the vasopressin system, the renin-angiotensin system (RAS) and the sympathetic system. Basal haemodynamic data, baroreflex evaluation and AP responses to blockade of the vasopressin system with vasopressin V(1) receptor antagonist (aAVP; 10 mg/kg, i.v.), the RAS by losartan (10 mg/kg, i.v.) and the sympathetic system by hexamethonium (20 mg/kg, i.v.) were determined. 3. Glycaemia was similar between C and C-S (P = 0.612) and between D and D-S (P = 0.552), but higher in diabetic compared with non-diabetic rats (P < 0.0001). The D-S rats had an increment of 24% in mean AP compared with D (120 +/- 4 vs 97 +/- 2 mmHg, respectively; P = 0.0001), which was not seen in C-S compared with C rats. A positive association was noted between urinary sodium and mean AP (r = 0.37; P = 0.04). Plasma renin was undetectable in D-S rats. The response to acute drug blockade of vasopressin and the RAS was similar among groups, but hexamethonium elicited a more pronounced decrease in AP in D-S compared with D rats (P = 0.001). 4. The main neurohumoral mechanisms of salt-induced cardiovascular changes in STZ-diabetes are increased sodium and vascular sensitivity to adrenergic stimuli, which act in combination to produce a final result of higher AP levels, a finding not observed in control rats. Baroreflex derangements induced by diabetes were not affected by salt overload.

Angiotensin‐converting enzyme activity in plasma and tissues of spontaneously hypertensive rats after the short‐ and long‐term intake of hydrolysed egg white

This paper evaluates the effects of the short- (1 g/kg) and long-term (0.5 and 1 g/kg/day) oral intake of egg white hydrolysed with pepsin (hEW) and the long-term oral intake (1 g/kg/day) of egg white (EW) on local angiotensin-converting enzyme (ACE) activities in plasma and other tissues of spontaneously hypertensive rats (SHR), as compared to the effect of the ACE inhibitor prototype captopril. The rats treated with hEW were classed in a different group than the control rats and the rats treated with EW by cluster analysis, taking into account their tissue ACE activities and their systolic blood pressure (SBP). Principal component analysis (PCA) showed that SBP in SHR was negatively related with ACE activity in plasma and positively related with ACE activity in aorta and kidney. ACE activity in plasma significantly increased after the long-term treatment with hEW (0.5 g/kg/day). ACE activity in aorta and kidney was significantly inhibited 4 h after the short-term administration of hEW. The long-term treatment with hEW caused local effects on ACE activity in aorta, kidney and lungs that followed a pattern similar, but less pronounced, than that caused by captopril.

Clinical Effects Produced by a Standardized Herbal Medicinal Product of Hibiscus sabdariffa on Patients with Hypertension. A Randomized, Double-blind, Lisinopril-Controlled Clinical Trial

Hibiscus sabdariffa L. (Malvaceae) has been used in different countries as an antihypertensive. Pharmacological work has demonstrated that this effect is probably produced by a diuretic activity and inhibition of the angiotensin-converting enzyme (ACE). Two clinical trials have confirmed the antihypertensive effect using watery infusions, in which a natriuretic effect was also detected. To compare therapeutic effectiveness, tolerability, and safety, as well as the effect on serum electrolytes and the ACE inhibitory effect of a herbal medicinal product prepared from the dried extract of H. sabdariffa calyxes (HsHMP) with those of lisinopril on patients with hypertension (HT), a randomized, controlled, and double-blind clinical trial was conducted. Patients of either sex, 25 - 61 years of age, with hypertension stage I or II, were daily treated for 4 weeks with the HsHMP, 250 mg of total anthocyanins per dose (experimental group), or 10 mg of lisinopril (control group). Outcome variables included effectiveness (diastolic blood pressure [DBP] reduction, >or= 10 mmHg), safety (absence of pathological modifications in the biochemical tests of hepatic and renal function), tolerability (absence of intense side effects), effect on serum electrolytes, and effect on ACE activity. Basal analysis included 193 subjects (100 in the experimental group), while outcome variable analysis integrated 171. Results showed that the experimental treatment decreased blood pressure (BP) from 146.48/97.77 to 129.89/85.96 mmHg, reaching an absolute reduction of 17.14/11.97 mmHg (11.58/12.21%, p < 0.05). The experimental treatment showed therapeutic effectiveness of 65.12 % as well as tolerability and safety of 100 %. BP reductions and therapeutic effectiveness were lower than those obtained with lisinopril (p < 0.05). Under the experimental treatment, the serum chlorine level increased from 91.71 to 95.13 mmol/L (p = 0.0001), the sodium level showed a tendency to decrease (from 139.09 to 137.35, p = 0.07), while potassium level was not modified. ACE plasmatic activity was inhibited by HsHMP from 44.049 to 30.1 Units (Us; p = 0.0001). In conclusion, the HsHMP exerted important antihypertensive effectiveness with a wide margin of tolerability and safety, while it also significantly reduced plasma ACE activity and demonstrated a tendency to reduce serum sodium (Na) concentrations without modifying potassium (K) levels. Further studies are necessary for evaluating the dose-dependency of HsHMP and for detecting lower effective doses.

Increased plasma substance P and CGRP levels, and high ACE activity in migraineurs during headache-free periods

Substance P (SP), calcitonin gene-related peptide (CGRP), and angiotensin converting enzyme (ACE) may have roles in trigeminovascular nociceptive mechanisms. We investigated interictal levels of SP, CGRP, ACE activity, and their correlation, in a sample of migraineurs. Forty-one patients suffering from migraine with aura (MA), 54 without aura (MO), and 52 non-headache subjects (controls) participated in this study. Blood samples were collected from cubital veins. Plasma levels of SP and CGRP were measured by enzyme immunoassay. Plasma ACE activities were measured spectrophotometrically. SP levels in MA (6.6 ± 3.7 pg/ml; mean ± SD) and MO (6.6 ± 3.2 pg/ml) were significantly higher than in controls (4.8 ± 2.4 pg/ml) ( P < 0.01). CGRP levels in MA (18.8 ± 8.8 pg/ml) and MO (19.1 ± 9.4 pg/ml) were also significantly higher than in controls (13.4 ± 4.4 pg/ml) ( P < 0.01). ACE activities in MA (34.6 ± 19.0 U/l) were significantly higher than in MO (25.3 ± 13.2 U/l) and controls (27.0 ± 20.4 U/l) ( P < 0.05). There was a significant correlation between SP and CGRP levels ( P < 0.05). In MA, SP and CGRP showed a tendency toward positive correlation, which was not significant. There was a weak, but significant positive correlation between SP levels and ACE activities ( P < 0.01). However, a relationship between ACE activities and CGRP levels was not observed. The data suggest that SP, CGRP, and ACE are relevant to migraine pathophysiology, and that they may interact.

Vasopeptidase Inhibition Prevents Target Organ Damage and Improves Survival in Spontaneously Hypertensive Rats

Vasopeptidase inhibition has been shown to be an effective antihypertensive principle but its long-term effects on hypertensive target organ damage are not known. We investigated the myocardial, vascular and renal effects of chronic vasopeptidase inhibition in arterial hypertension. One hundred and thirty-nine male spontaneously hypertensive rats aged 15 months were treated chronically with either the pure angiotensin-converting enzyme (ACE) inhibitor, ramipril (1 mg/kg/d in drinking water, n=46), or the vasopeptidase inhibitor AVE7688 (30 mg/kg/d in chow, n=46), or placebo (n=47) and followed up until they died. After six months, both ramipril and AVE7688 had markedly reduced plasma ACE activity, normalised blood pressure (BP), reduced left ventricular mass and improved systolic function to similar extents. Acetylcholine mediated relaxation of aortic rings was improved by both ramipril and AVE7688. There was substantial albuminuria in the placebo group (albumin-to-creatinine ratio 107+/-54 microg/mg), which was significantly reduced by ramipril to 57+/-34 microg/mg, and practically abolished in the AVE7688 group (22+/-12 microg/mg, p<0.05 vs. placebo and ramipril). Tubulo-interstitial damage (semi-quantitative score) was significantly reduced by AVE7688 and ramipril. Overall mortality was markedly reduced in the ramipril and AVE7688 groups (13% and 16% at six months, respectively), both p<0.05 vs. placebo (71%). Vasopeptidase inhibition effectively controls BP and reduces myocardial, vascular and renal target organ damage, resulting in a markedly prolonged survival. At similar degrees of plasma ACE inhibition, AVE7688 compared to ramipril offers superior protection against hypertensive kidney damage.

Induction of Heme Oxygenase

Carbon monoxide (CO), produced within the body as a product of the catabolism of heme by the enzyme heme oxygenase (HO), has been reported to be a local vasodilator. One of its possible pathways is to stimulate guanylyl cyclase to produce cGMP as a second messenger.1 The parallel to NO, another gaseous signaling molecule that also works through cGMP-mediated pathways (although more potent), is obvious. In fact, the vasodilator actions of these 2 may be integrally linked. Both are endothelium derived.2 NO stimulation of cGMP may facilitate CO-mediated dilation of resistance vessels through calcium-activated potassium channels.3 However, the HO–CO story has not received the same interest and attention as NO, nor is it as generally well understood by those who work outside the field. In the present issue, we are presented with a provocative study by one of the well-established laboratories within the field of HO–CO. Wang et al4 focus on HO in the genetic model of hypertension, the spontaneously hypertensive rat (SHR). They report that 3 weeks of administration of hemin, the oxidation product of heme, which is both a substrate for and an inducer of HO, produced a profound 80-mmHg decrease in blood pressure that was sustained completely for 9 months after ceasing treatment (a duration in a rat’s life, which roughly translates into 17.5 human years). Although this is a remarkable, hopeful, and possibly profound observation, the study probably raises more questions than it answers. First, it is important to point out that this sustained decrease in blood pressure and reversal of hypertension is an unprecedented result. The potential importance of this observation is that a single 3-week treatment regimen induced a protracted reduction in blood pressure, long after treatment had ceased. To put this in perspective, treatment of virtually all forms of …

Pharmacokinetic and Pharmacodynamic Parameters of Ramipril and Ramiprilat in Healthy Dogs and Dogs with Reduced Glomerular Filtration Rate

Ramipril, an angiotensin‐converting enzyme (ACE) inhibitor for use in dogs, is converted in vivo to its active form, ramiprilat, which is eliminated in the bile and urine in the dog. The objective of this study was to assess the effect of renal impairment on the pharmacokinetics (PKs) and pharmacodynamics (PDs) of ramipril and ramiprilat. Ten adult Beagle dogs were used. PK/PD studies were performed before and after the induction of subclinical renal impairment. Ramiprilat was given at 0.25 mg/kg by a single IV bolus. After a 2‐week washout period, ramipril was administered PO at 0.25 mg/kg once daily for 8 days. Ramipril and ramiprilat PKs were studied by using a physiologically based model. The relationship between free plasma ramiprilat concentration and ACE activity was described by using the fractional Hill model. Glomerular filtration rate was decreased by 58%. No biologically relevant changes in usual plasma variables were observed between the 1st and the 8th day of oral treatment with ramipril under either condition. After an IV bolus of ramiprilat, the only changes in renal‐impaired dogs were a 14 and 49% decrease in clearance of the free fraction of ramiprilat (P &lt;.01) and free plasma concentration required to produce 50% of the maximal effect (P &lt;.05), respectively. After repeated PO administration of ramipril, there were no alterations in any of the PK and PD parameters in healthy or renal‐impaired dogs. No adjustment of the recommended PO dosage of ramipril is needed in dogs with moderate renal impairment.

Acute Blood Pressure Effects and Chronic Hypotensive Action of Calcimimetics in Uremic Rats

A previous study in subtotally nephrectomized (SNX) rats suggested beneficial effects of the calcimimetic R-568 beyond the control of mineral metabolism. This study analyzed potential blood pressure (BP)-lowering effects of R-568. Male Sprague-Dawley rats received two-stage subtotal nephrectomy or sham operation. Telemetry devices were inserted into the abdominal aorta, and BP was measured every 5 min. R-568 (20 mg/kg per d) or solvent was infused for 4 wk followed by once-daily subcutaneous injections for 2 wk. Total body sodium was measured by neutron activation analysis. The uremia-induced increase of mean arterial pressure from baseline to day 42 in SNX solvent rats (103+/-5 to 128+/-14 mmHg, P=0.006) was attenuated by R-568 (104+/-5 to 111+/-8 mmHg; P<0.0001 for difference of slopes). The circadian rhythm was abrogated in SNX rats and not restored by R-568. In sham-operated rats, R-568 had only a minor transient antihypertensive effect. R-568 injection induced a transient rise of mean arterial pressure by 23+/-4 and 26+/-10 mmHg in sham and SNX rats but only by 9+/-3 and 10+/-5 mmHg in solvent-treated rats (P<0.01 versus baseline and solvent versus R-568). Plasma angiotensin-converting enzyme activity and aldosterone levels were similar; food intake and physical activity did not differ throughout the study. In healthy rats, total body sodium was higher after 14 d of R-568 compared with solvent infusion (37.1+/-4 versus 32.5+/-1.4 mmol/kg; P=0.01). The calcimimetic R-568 causes an initial BP increase in sham-operated and uremic rats, which in uremic rats is followed by a marked and sustained antihypertensive effect.

The Effect of Ramipril on Left Ventricular Mass, Myocardial Fibrosis, Diastolic Function, and Plasma Neurohormones in Maine Coon Cats with Familial Hypertrophic Cardiomyopathy without Heart Failure

Hypertrophic cardiomyopathy (HCM) is the most common heart disease of cats, resulting in left ventricular (LV) hypertrophy, myocardial fibrosis, and diastolic dysfunction. Ramipril will reduce LV mass, improve diastolic function, and reduce myocardial fibrosis in cats with HCM without congestive heart failure (CHF). This prospective, blinded, placebo-controlled study included 26 Maine Coon and Maine Coon cross-bred cats with familial HCM but without CHF. Cats were matched for LV mass index (LVMI) and were randomized to receive ramipril (0.5 mg/kg) or placebo q24h for 1 year, with investigators blinded. Plasma brain natriuretic peptide (BNP) concentration, plasma aldosterone concentration, Doppler tissue imaging (DTI), and systolic blood pressure were measured at baseline and every 3 months for 1 year. Cardiac magnetic resonance imaging (cMRI) was performed to quantify LV mass and myocardial fibrosis by delayed enhancement (DE) cMRI at baseline and 6 and 12 months. Plasma angiotensin-converting enzyme (ACE) activity was measured on 16 cats 1 hour after PO administration. Plasma ACE activity was adequately suppressed (97%) in cats treated with ramipril. LV mass, LVMI, DTI, DE, blood pressure, plasma BNP, and plasma aldosterone were not different in cats treated with ramipril compared with placebo (P = .85, P = .94, P = .91, P = .89, P = .28, P = .18, and P = .25, respectively). Treatment of Maine Coon cats with HCM without CHF with ramipril did not change LV mass, improve diastolic function, alter DE, or alter plasma BNP or aldosterone concentrations in a relevant manner.