Activation of the renin-angiotensin system in dogs with asymptomatic and mildly symptomatic mitral valvular insufficiency

Beyond Angiotensin-Converting Enzyme Inhibitors: Modulation of the Renin-Angiotensin-Aldosterone System to Delay or Manage Congestive Heart Failure

The renin-angiotensin-aldosterone system (RAAS) consists of bioactive angiotensin peptides, enzymatic pathways, receptors, and the steroid hormone aldosterone. The RAAS regulates blood pressure, sodium, and electrolyte homeostasis and mediates pathologic disease processes. Within this system is an alternative arm that counterbalances the vasoconstrictive, sodium and water retentive, and pro-fibrotic and inflammatory effects of the classical arm. Improved biochemical methodologies in RAAS quantification are elucidating how this complex system changes in health and disease. Future treatments for cardiovascular and kidney disease will likely involve a more nuanced manipulation of this system rather than simple blockade.

Changes in renin-angiotensin-aldosterone system during cardiac remodeling after mitral valvuloplasty in dogs

BACKGROUND

Information regarding changes in renin-angiotensin-aldosterone system (RAAS) during cardiac remodeling after mitral valvuloplasty (MVP) in dogs remains lacking.

HYPOTHESIS/OBJECTIVES

To assess the longitudinal effects of MVP on circulating RAAS activity.

ANIMALS

Eight client-owned dogs receiving MVP for myxomatous mitral valve disease (MMVD).

METHODS

This is a cohort study. Plasma renin activity (PRA), angiotensin II (AT2), aldosterone (PAC), blood urea nitrogen (BUN), and creatinine concentrations, were measured in these dogs before (baseline) and at 3 consecutive monthly follow-ups (Post-1M, Post-2M, Post-3M). Echocardiography was concomitantly used to assess the process of cardiac recovery after MVP.

RESULTS

The echocardiography revealed a significant decrease in LVIDDN, LA/Ao, FS, E velocity, E/A, E' sep, S' lat, E' lat, and A' lat after MVP compared with baseline (P < .05). There was a significant reduction in the PRA (2.45, 3.05, 2.74 vs 8.8 ng/mL/h; P = .002), AT2 (466, 315, 235 vs 1200 pg/mL; P = .009), and PAC (39.88, 47, 54.62 vs 179.5 pg/mL; P = .01), respectively at Post-1M, Post-2M, Post-3M compared to the baseline. Additionally, BUN and creatinine concentrations decreased from Post-1M. The RAAS variables showed significant, weak to moderate, relationship with selected echocardiographic variables.

CONCLUSIONS AND CLINICAL IMPORTANCE

Mitral valvuloplasty contributes to decreased RAAS activity in MMVD dogs, which paralleled the process of cardiac reverse remodeling up to Post-3M. This information facilitates formulating strategies to optimize clinical outcomes for dogs after MVP.

COVID-19: imbalance of multiple systems during infection and importance of therapeutic choice and dosing of cardiac and anti-coagulant therapies

The renin-angiotensin-aldosterone system and its metabolites play an important role in homeostasis of body, especially the cardiovascular system. In this study, we discuss the imbalance of multiple systems during the infection and the importance of therapeutic choice, dosing, and laboratory monitoring of cardiac and anti-coagulant therapies in COVID-19 patients. The crosstalk between angiotensin, kinin-kallikrein system, as well as inflammatory and coagulation systems plays an essential role in COVID-19. Cardiac complications and coagulopathies imply the crosstalks between the mentioned systems. We believe that the blockage of bradykinin can be a good option in the management of COVID-19 and CVD in patients and that supportive treatment of respiratory and cardiologic complications is needed in COVID-19 patients. Ninety-one percent of COVID-19 patients who were admitted to hospital with a prolonged aPTT were positive for lupus anticoagulant, which increases the risk of thrombosis and prolonged aPTT. Therefore, the question that is posed at this juncture is whether it is safe to use the prophylactic dose of heparin particularly in those with elevated D-dimer levels. It should be noted that timing is of high importance in anti-coagulant therapy; therefore, we should consider the level of D-dimer, fibrinogen, drug-drug interactions, and risk factors during thromboprophylaxis administration. Fibrinogen is an independent predictor of resistance to heparin and should be considered before thromboprophylaxis. Alteplase and Futhan might be a good choice to assess the condition of heparin resistance. Finally, the treatment option, dosing, and laboratory monitoring of anticoagulant therapy are critical decisions in COVID-19 patients.

Factors affecting the urinary aldosterone-to-creatinine ratio in healthy dogs and dogs with naturally occurring myxomatous mitral valve disease

BACKGROUND

Chronic renin-angiotensin-aldosterone system (RAAS) activation in course of heart diseases contributes to cardiac remodeling and heart failure. Myxomatous mitral valve disease (MMVD) is characterized by different stages of severity and trend of RAAS activity during the course of the disease is still uncertain. The urinary aldosterone-to-creatinine ratio (UAldo:C) has been proven to reflect RAAS activation in dogs and might be a useful marker in monitoring therapy and disease progression, but data about this parameter need to be expanded. The objective of this study was to evaluate the UAldo:C in healthy dogs and dogs with naturally occurring MMVD, and to investigate the relationships between this parameter and clinical, echocardiographic and laboratory variables.

RESULTS

The study population consisted of 149 dogs: 49 healthy and 100 MMVD dogs (45 stage B1, 13 stage B2 and 42 stage C). Urinary aldosterone-to-creatinine ratio was not significantly different among healthy and MMVD dogs of any stages. Breed, sex and age showed a significant impact on UAldo:C. In particular, Chihuahua and Cavalier King Charles spaniel showed significantly higher UAldo:C than other breeds, as well as intact females than other genders. In stage C dogs, UAldo:C appeared to be increased by spironolactone and was positively associated with furosemide dose (P = 0.024). Aldosterone breakthrough (ABT) appeared to occur in 36% (8/22) of stage C dogs not receiving spironolactone. A significant positive association between UAldo:C and left atrium-to-aortic root ratio (LA/Ao) was found.

CONCLUSIONS

Individual factors such as breed, sex and age appeared to influence UAldo:C, and therapy seemed to add further variability. In the light of these results, comparing the UAldo:C of a single patient with a population-based reference value might lead to wrong interpretations and an individual monitoring should be considered. The prevalence of ABT in the present study (36%) was in line with those previously reported. However, due to the high individual variability of UAldo:C found in the study, even this result should be re-evaluated in the setting of an individual longitudinal approach. The positive association between UAldo:C and LA/Ao supports the mutual relationship between RAAS and cardiac remodeling.

Effect of angiotensin receptor blockers and angiotensin converting enzyme 2 on plasma equilibrium angiotensin peptide concentrations in dogs with heart disease

BACKGROUND

The pathophysiology of heart failure involves maladaptive angiotensin peptides (APs) and enzymes, including angiotensin 2 (AT2) and angiotensin converting enzyme (ACE), as well as recently described alternative components, such as angiotensin 1-7 (Ang1-7) and angiotensin converting enzyme 2 (ACE2). The relative effects of different neurohormonal-targeting drugs on balance of APs in dogs with heart disease are unknown.

HYPOTHESIS/OBJECTIVES

Plasma AP concentrations differ in dogs receiving angiotensin converting enzyme inhibitors (ACEIs) vs angiotensin receptor blockers (ARBs) and recombinant human ACE2 (rhACE2) will further increase these differences.

ANIMALS

Eight dogs with degenerative mitral valve disease (DMVD).

METHODS

Prospective open-label trial. Equilibrium concentrations of APs from plasma during PO ACEI treatment and then after 14 days of PO ARB treatment using telmisartan were measured using liquid chromatography-tandem mass spectroscopy before and after in vitro incubation with rhACE2.

RESULTS

Concentration of Ang1-7 was increased during ARB treatment (Ang1-7: 443 pg/mL; 95% confidence interval [CI] = 247-794 pg/mL) vs ACEI (Ang1-7: 182 pg/mL; 95% CI = 66.2-503 pg/mL; P = .01). Incubation with rhACE2 decreased traditional APs while increasing beneficial alternative APs, and Ang1-7 was significantly higher in the ARB + rhACE2 (880 pg/mL; 95% CI = 560-1383 pg/mL) vs ACEI + rhACE2 (455 pg/mL; 95% CI = 188-1104 pg/mL; P = .03) group. The most favorable theoretical AP profile was achieved in the ARB + rhACE2 group.

CONCLUSIONS AND CLINICAL IMPORTANCE

The AP profile during telmisartan treatment is associated with higher plasma Ang1-7 as compared with during ACEI. This favorable shift is potentiated in vitro by combination of ARB + rhACE2. These data support potential AP-targeting strategies and drugs in dogs with DMVD.

Correction of serum chloride concentration in dogs with congestive heart failure

Background

Hypochloremia associated with congestive heart failure (CHF) in dogs is likely multifactorial. Loop diuretics cause 1:2 sodium [Na⁺]:chloride [Cl⁻] loss, whereas water retention causes a 1:1 [Na⁺]:[Cl⁻] dilution. Mathematical [Cl⁻] correction separates these effects on [Cl⁻].

Hypothesis

We hypothesized that corrected [Cl⁻] (c[Cl⁻]) would not differ from measured [Cl⁻] (m[Cl⁻]) in dogs with controlled CHF because of loop diuretics, and dogs with refractory CHF would have higher c[Cl⁻] than m[Cl⁻], indicating relative water excess.

Animals

Seventy‐one client‐owned dogs with acquired heart disease, without CHF (NO‐CHF), 76 with Stage C CHF and 24 with Stage D CHF.

Methods

Clinicopathological data from a previous study were retrospectively analyzed. Corrected [Cl⁻], m[Cl⁻], and differences were compared among NO‐CHF, Stage C CHF, and Stage D CHF, using the formula: c[Cl⁻] = (mid‐reference range [Na⁺]/measured [Na⁺]) × m[Cl⁻].

Results

Corrected [Cl⁻] and m[Cl⁻] were lower in Stage D vs Stage C and NO‐CHF (all P < .0001). The c[Cl⁻] was higher than m[Cl⁻] in Stage D (P < .0001) but not Stage C or NO‐CHF. Median difference between c[Cl⁻] and m[Cl⁻] was higher for Stage D vs Stage C (P = .0003). No hypochloremic Stage D dogs had normal c[Cl⁻], but 11/24 had [Cl⁻] that was increased by >2 mmol/L.

Conclusions and Clinical Importance

Serum [Cl⁻] increased after mathematical correction in Stage D CHF dogs but not in Stage C and NO‐CHF dogs. Although c[Cl⁻] was higher than m[Cl⁻] in Stage D dogs supportive of relative water excess, hypochloremia persisted, consistent with concurrent loop diuretic effects on electrolytes. Future study correlating c[Cl⁻] to antidiuretic hormone concentrations is warranted.

Plasma and tissue angiotensin-converting enzyme 2 activity and plasma equilibrium concentrations of angiotensin peptides in dogs with heart disease

BACKGROUND

Angiotensin-converting enzyme 2 (ACE2) is a homologue of angiotensin-converting enzyme (ACE) and produces angiotensin peptides (APs), such as angiotensin 1-9 and 1-7 that are vasodilatory and natriuretic, and act to counterbalance angiotensin II.

HYPOTHESIS

Evidence of ACE2 can be found in tissues and plasma of dogs. Equilibrium concentrations of renin angiotensin aldosterone system (RAAS) APs differ in dogs with heart disease compared to healthy dogs and recombinant human ACE2 (rhACE2) alters relative concentrations of APs.

ANIMALS

Forty-nine dogs with and 34 dogs without heart disease.

METHODS

Immunohistochemistry and assays for tissue and plasma ACE2 activity and equilibrium concentrations of plasma RAAS APs were performed.

RESULTS

Immunolabeling for ACE2 was present in kidney and myocardial tissue. Median plasma ACE2 activity was significantly increased in dogs with congestive heart failure (CHF; 6.9 mU/mg; interquartile range [IQR], 5.1-12.1) as compared to control (2.2 mU/mg; IQR, 1.8-3.0; P = .0003). Plasma equilibrium analysis of RAAS APs identified significant increases in the median concentrations of beneficial APs, such as angiotensin 1-7, in dogs with CHF (486.7 pg/mL; IQR, 214.2-1168) as compared to those with preclinical disease (41.0 pg/mL; IQR, 27.4-45.1; P < .0001) or control (11.4 pg/mL; IQR, 7.1-25.3; P = .01). Incubation of plasma samples from dogs with CHF with rhACE2 increased beneficial APs, such as angiotensin 1-9 (preincubation, 10.3 pg/mL; IQR, 4.4-37.2; postincubation, 2431 pg/mL; IQR, 1355-3037; P = .02), while simultaneously decreasing maladaptive APs, such as angiotensin II (preincubation, 53.4 pg/mL; IQR, 28.6-226.4; postincubation, 2.4 pg/mL; IQR, 0.50-5.8; P = .02).

CONCLUSIONS AND CLINICAL IMPORTANCE

Recognition of the ACE2 system expands the conventional view of the RAAS in the dog and represents an important potential therapeutic target.

Effects of high-dose alacepril on left atrial pressure and central aortic pressure in awake dogs with mitral valve regurgitation

The purpose of this study was to clarify how alacepril in amounts greater than those recommended on the product labeling approved by drug regulatory agencies affects left atrial pressure (LAP) and central aortic pressure in dogs with experimentally induced mitral valve regurgitation (MR). Six healthy Beagle dogs were surgically induced for MR and received alacepril at either 1.5mg/kg/12-h (3.0mg/kg/day) or 3.0mg/kg/12-h (6.0mg/kg/day) per one administration for seven days. After a four-week washout period, another dosage was administrated as a crossover study. Dogs were randomised to receive 3.0mg/kg/day or 6.0mg/kg/day first. LAP and central systolic (SAP), mean (MAP), and diastolic (DAP) aortic pressure were measured for 24-h before and during the administration of alacepril. The earliest decreases in SAP, MAP, and DAP with 6.0mg/kg/day were observed on days 4, 4, and 5, respectively. With 3.0mg/kg/day, the earliest decrease in DAP was observed on day 7. The maximum LAP was decreased on days 5 and 7 with 6.0mg/kg/day. The mean LAP was decreased on day 7 with 6.0mg/kg/day. In conclusion, the administration of alacepril at 6.0mg/kg/day reduced the LAP and central aortic pressure within several days.

Effects of the angiotensin-converting enzyme inhibitor alacepril in dogs with mitral valve disease

Alacepril is a relatively novel angiotensin-converting enzyme inhibitor; however, the safety, tolerance, and efficacy of alacepril in terms of cough suppression in dogs with mitral valve disease (MVD) remain unknown. The aim of this study was to investigate the safety, tolerance, and cough suppression efficacy of alacepril in dogs with MVD. This was a multi-center, prospective study. Forty-two dogs with echocardiographic or radiographic evidence of cardiac enlargement in addition to cough were enrolled. Dogs were treated with alacepril (1.0-3.0 mg/kg/day) for at least 4 weeks. One dog (2.4%) developed complications, including appetite loss, lethargy, and vomiting. Thirty-six dogs were re-evaluated after 4 weeks of treatment. Cough resolved or improved in 20 dogs (55.6%) after treatment. Based on the efficacy of alacepril, the dogs were divided into an effective group (n=20) and an ineffective group (n=16). After treatment, the left ventricular end-diastolic internal diameter corrected for body weight was significantly increased from baseline in the ineffective group but was significantly decreased in the effective group. Univariate binomial logistic regression analyses showed that high atrial natriuretic peptide level, N-terminal pro-B-type natriuretic peptide level, and E wave velocity at baseline were significantly correlated with alacepril inefficacy. Alacepril as treatment for MVD is well tolerated in most dogs, and different conditions of cardiac loading may influence the effect of the drug. Alacepril is expected to improve the quality of life of dogs with early stage MVD.

Preliminary investigation of orally administered benazepril in horses with left-sided valvular regurgitation

BACKGROUND

Despite the paucity of data available, orally administered angiotensin-converting enzyme (ACE) inhibitors are empirically used in horses with valvular regurgitation.

OBJECTIVE

Evaluate the echocardiographic and hormonal changes in response to oral benazepril in horses with left-sided valvular regurgitation.

STUDY DESIGN

Prospective, randomised double-blind, placebo-controlled trial.

METHODS

Horses with mitral valve (MR) and/or aortic valve regurgitation (AR) received oral benazepril (n = 6) at a dosage of 1 mg/kg q 12 h or a placebo (n = 5) for 28 days. Echocardiography was performed before drug administration and after 28 days of treatment. Plasma renin activity, serum ACE activity, angiotensin II concentration, aldosterone concentration and biochemical variables were measured before drug administration and after 7 and 28 days of treatment.

RESULTS

Relative to baseline, horses treated with benazepril had statistically significant reduction in left ventricular internal diameter in systole (mean difference between groups = -0.97 cm; 95% CI = -1.5 to -0.43 cm), aortic sinus diameter (-0.31 cm; -0.54 to -0.07 cm), and percentage of the aortic annulus diameter occupied by the base of the AR jet (-17.05%; -31.17 to -2.93%) compared with horses receiving a placebo. In addition, horses treated with benazepril had a significantly greater increase in cardiac output (11.95 L/min; 1.17-22.73 L/min) and fractional shortening (7.59%; 3.3-11.88%) compared with horses receiving a placebo. Despite profound serum ACE inhibition, renin activity and concentrations of angiotensin II and aldosterone were not significantly different between treatment groups or among time points.

MAIN LIMITATIONS

Very small sample size and short treatment period.

CONCLUSIONS

Treatment with oral benazepril resulted in statistically significant echocardiographic changes that might indicate reduced cardiac afterload in horses with left-sided valvular regurgitation. Additional studies with a larger sample size will be necessary to determine if administration of benazepril is beneficial in horses with valvular regurgitation. The Summary is available in Spanish - see Supporting Information.

Treatment of dogs with compensated myxomatous mitral valve disease with spironolactone-a pilot study

OBJECTIVES

Spironolactone improves outcome in dogs with advanced myxomatous mitral valve disease (MMVD). Its efficacy in preclinical MMVD is unknown. The hypothesis was the administration of spironolactone to dogs with compensated MMVD demonstrating risk factors for poorer prognosis will decrease the rate of disease progression. The aim was to provide pilot data to evaluate preliminary effects and sample size calculation for a definitive clinical trial.

ANIMALS

Twenty-five client-owned dogs with MMVD with at least one of the following; left atrial to aortic ratio (LA:Ao) ≥ 1.5, normalized left ventricular internal diameter in diastole ≥ 1.6), N-terminal pro-B-type natriuretic peptide (NT-proBNP) > 550 pmol/L, cardiac troponin I > 0.025 ng/mL.

METHODS

Prospective, single-center, equally randomized, placebo-controlled, double-blinded, parallel grouped pilot study. No dogs were receiving medications for cardiac disease before the enrollment.

RESULTS

Twelve dogs received placebo; 13 received spironolactone. One dog in the spironolactone group died suddenly, 1 developed congestive heart failure, and 2 received suboptimal spironolactone doses. At enrollment, NT-proBNP was significantly higher in the spironolactone group (p=0.005). Left atrial to aortic ratio (p=0.002) and left ventricular internal diameter in diastole (p=0.005) increased over time in the placebo group, but not the spironolactone group; the change did not differ significantly between groups. The change in biomarker concentrations did not differ significantly between groups; there was a tendency toward an increase in NT-proBNP over time in the placebo group. Enrollment of 76 dogs would be necessary to demonstrate a difference in the change in LA:Ao over 6 months between the groups.

CONCLUSIONS

Preliminary results support undertaking a larger clinical trial of treatment of dogs with preclinical MMVD with spironolactone.

Associations among serum N-terminal procollagen type III concentration, urinary aldosterone-to-creatinine ratio, and ventricular remodeling in dogs with myxomatous mitral valve disease

OBJECTIVE

To assess relationships among serum N-terminal procollagen type III concentration, urinary aldosterone-to-creatinine concentration ratio (UAC), and clinical variables in dogs with myxomatous mitral valve disease (MMVD) and healthy dogs.

ANIMALS

162 dogs with MMVD and 24 healthy control dogs of comparable age and body weight.

PROCEDURES

Blood and urine samples were collected from each dog. Dogs with MMVD underwent echocardiography and ECG. Ventricular diameter measurements were normalized for body weight. Serum N-terminal procollagen type III and urinary aldosterone concentrations were measured via radioimmunoassay. Each dog was examined on 1 to 3 occasions. Examinations were repeated at approximately 6-month intervals.

RESULTS

Serum N-terminal procollagen type III concentration decreased with increasing severity of MMVD and was negatively associated with age and left ventricular end-diastolic and end-systolic diameters. The UAC increased with prior percentage change in left ventricular end-diastolic diameter per month, subsequent percentage change in left ventricular end-systolic diameter per month, and treatment with diuretics and was negatively associated with age. Both UAC and serum N-terminal procollagen type III concentration were higher in Cavalier King Charles Spaniels than in other breeds when other measured variables were controlled for.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs with MMVD, echocardiographic indicators of left ventricular remodeling appeared to be associated with a decrease in serum concentration of a marker of collagen type III turnover and an increase in urinary aldosterone concentration.

Prevalence of mitral valve prolapse in residents living at moderately high altitude

OBJECTIVE

Prolapse of mitral valve leaflets is a frequent disorder and the most common cause of severe mitral regurgitation in western countries. However, little is known about the effects of altitude on mitral valve prolapse. We studied the prevalence and echocardiographic characteristics of mitral valve prolapse at moderately high altitude and sea level.

METHODS

A total of 936 consecutive subjects who were admitted to 2 study institutions at Kars, Turkey (1750 m) and Istanbul, Turkey (7 m) were enrolled in this study to determine prevalence of mitral valve prolapse. Demographic and 2-dimensional echocardiographic characteristics of participants were recorded.

RESULTS

Prevalence of mitral valve prolapse was found to be significantly higher in people living at moderate altitude compared with those living at sea level (6.2% vs 2.0%; P = .007). Overall echocardiographic features regarding valve thickness (4.1 ± 0.80 mm vs 3.6 ± 0.66 mm; P = 0.169), maximal valve prolapse (4.6 ± 2.08 mm vs 3.9 ± 0.91 mm; P = .093), and frequency of mitral regurgitation (89% vs 73%; P = .65) were similar between groups, although anterior valve prolapse was seen more frequently at moderate altitude (50% vs 11%; P = .056) and posterior leaflet prolapse was significantly more frequent at sea level (66% vs 10%; P = .002).

CONCLUSIONS

Mitral valve prolapse is more frequently observed at moderately high altitudes. Further studies are needed to determine clinical importance of our findings.

Effects of furosemide and the combination of furosemide and the labeled dosage of pimobendan on the circulating renin-angiotensin-aldosterone system in clinically normal dogs

OBJECTIVE

To evaluate the effect of administration of the labeled dosage of pimobendan to dogs with furosemide-induced activation of the renin-angiotensin-aldosterone system (RAAS).

ANIMALS

12 healthy hound-type dogs.

PROCEDURES

Dogs were allocated into 2 groups (6 dogs/group). One group received furosemide (2 mg/kg, PO, q 12 h) for 10 days (days 1 to 10). The second group received a combination of furosemide (2 mg/kg, PO, q 12 h) and pimobendan (0.25 mg/kg, PO, q 12 h) for 10 days (days 1 to 10). To determine the effect of the medications on the RAAS, 2 urine samples/d were obtained for determination of the urinary aldosterone-to-creatinine ratio (A:C) on days 0 (baseline), 5, and 10.

RESULTS

Mean ± SD urinary A:C increased significantly after administration of furosemide (baseline, 0.37 ± 0.14 μg/g; day 5, 0.89 ± 0.23 μg/g) or the combination of furosemide and pimobendan (baseline, 0.36 ± 0.22 μg/g; day 5, 0.88 ± 0.55 μg/g). Mean urinary A:C on day 10 was 0.95 ± 0.63 μg/g for furosemide alone and 0.85 ± 0.21 μg/g for the combination of furosemide and pimobendan.

CONCLUSIONS AND CLINICAL RELEVANCE

Furosemide-induced RAAS activation appeared to plateau by day 5. Administration of pimobendan at a standard dosage did not enhance or suppress furosemide-induced RAAS activation. These results in clinically normal dogs suggested that furosemide, administered with or without pimobendan, should be accompanied by RAAS-suppressive treatment.

EFFECTS OF MITRAL REGURGITATION ON THE REFLEX DIURESIS TO PULMONARY LYMPHATIC OBSTRUCTION IN RABBITS

Increasing the extravascular fluid of the airways acutely by obstructing pulmonary lymph drainage causes a reflex diuresis mediated by neuronal nitric oxide synthase in the renal medulla. The authors examined this reflex in rabbits with a chronic increase in extravascular fluid of the airways resulting from surgically induced mitral regurgitation. Intact rabbits served as controls. Renal neuronal (nNOS) and endothelial (eNOS) nitric oxide synthase expressions were also examined. The reflex was absent in rabbits with mitral regurgitation. There were significant increases in medullary and cortical nNOS mRNA compared to controls. The observed changes in mRNA levels correlated with nNOS protein levels. eNOS mRNA was unaffected.

Endogenous angiotensin II has fewer effects but neuronal nitric oxide synthase has excitatory effects on renal sympathetic nerve activity in salt-sensitive hypertension-induced heart failure

The effects of endogenous angiotensin II (Ang II) and neuronal nitric oxide synthase (nNOS) on tonic sympathetic activity were studied in salt-sensitive hypertension-induced heart failure. Dahl salt-sensitive rats were fed 8% NaCl diet for 9 weeks to induce chronic heart failure (CHF-DSS). The effects of intravenous administration of a selective nNOS inhibitor, S-methyl-L: -thiocitrulline (SMTC), and an Ang II type 1-receptor blocker, losartan, on renal sympathetic nerve activity (RSNA) were examined in chronically instrumented conscious rats. Baroreceptor (baro)-unloaded RSNA was obtained by decreasing arterial pressure with caval occlusion to determine tonic RSNA. SMTC significantly decreased baro-unloaded RSNA, and subsequent losartan recovered baro-unloaded RSNA to the control level in CHF-DSS rats. To compare the effects of the inhibitors between low- and high-activity states of the renin-angiotensin system (RAS), Sprague-Dawley rats were fed low (0.04%)- or high (8%)-salt diets. A significant difference was found in the effects of SMTC and/or losartan on RSNA between the high- and low-RAS states, which suggested that there is a difference in the effect of endogenous Ang II on RSNA between salt-induced and other-type heart failure. To examine the effects of heart failure on brain-tissue nNOS activity, we measured the activities of the diencephalon in heart-failure rats. Heart failure significantly suppressed diencephalon nNOS activity, which was significantly different from the results in salt-sensitive hypertension without heart failure. These results suggest that endogenous Ang II has fewer effects, but nNOS has excitatory effects on tonic RSNA in salt-sensitive hypertension-induced heart failure.

Evaluation of plasma and urinary levels of 6-keto-prostaglandin F1alpha as a marker for asymptomatic myxomatous mitral valve disease in dogs

Endothelial dysfunction might be involved in the pathogenesis of myxomatous mitral valve disease (MMVD). The aims of this study were (1) to validate an enzyme immunoassay (EIA) for canine 6-keto-prostaglandin (PG)F(1alpha) (prostacyclin metabolite and marker for endothelial function) and (2) to compare plasma and urinary 6-keto-PGF(1alpha) in dogs with asymptomatic MMVD. The study included two breeds predisposed to MMVD and two control groups (Cairn terriers and dogs of different breeds). Echocardiography was used to estimate the severity of MMVD. The intra- and inter-assay coefficients of variation were between 3.1% and 24.5% in the assay range. No echocardiographic parameter was correlated with plasma or urinary 6-keto-PGF(1alpha) (P>0.05), but all control dogs had lower urinary 6-keto-PGF(1alpha) (P<0.02) and the Cairn terriers had higher plasma 6-keto-PGF(1alpha) (P<0.02). The EIA appeared valid for measuring canine 6-keto-PGF(1alpha) in plasma and urine. It is suggested that 6-keto-PGF(1alpha) levels are related to breed and not MMVD in asymptomatic stages.

Modulation of the tissue reninangiotensin-aldosterone system in dogs with chronic mild regurgitation through the mitral valve

OBJECTIVE

To investigate whether the tissue and plasma renin-angiotensin-aldosterone system (RAAS) is activated in dogs with mild regurgitation through the mitral valve and determine the contribution of chymase and angiotensin-converting enzyme (ACE) to the activation of the RAAS and potential production of angiotensin II during the chronic stage of mild mitral valve regurgitation.

ANIMALS

5 Beagles with experimentally induced mild mitral valve regurgitation and 6 clinically normal (control) Beagles.

PROCEDURES

Tissue ACE and chymase-like activities and plasma RAAS were measured and the RAAS evaluated approximately 1,000 days after experimental induction of mitral valve regurgitation in the 5 dogs.

RESULTS

Dogs with experimentally induced mitral valve regurgitation did not have clinical signs of the condition, although echocardiography revealed substantial eccentric hyper- trophy. On the basis of these findings, dogs with mitral valve regurgitation were classified as International Small Animal Cardiac Health Council class Ib. Plasma activity of renin and plasma concentrations of angiotensin I, angiotensin II, and aldosterone were not significantly different between dogs with mitral valve regurgitation and clinically normal dogs. Tissue ACE activity was significantly increased and chymase-like activity significantly decreased in dogs with mitral valve regurgitation, compared with values in clinically normal dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

The tissue RAAS was modulated without changes in the plasma RAAS in dogs with mild mitral valve regurgitation during the chronic stage of the condition. An ACE-dependent pathway may be a major route for production of angiotensin II during this stage of the condition.

Aldosterone causes vasoconstriction in coronary arterioles of rats via angiotensin II type-1 receptor: Influence of hypertension

Aldosterone is involved in many cardiovascular diseases with increased oxidative stress. Aldosterone-induced cardiac fibrosis is abolished by blockade of angiotensin II Type-1 (AT1) receptor. Recently, non-genomic vasoconstrictor effects of aldosterone were reported in various vascular beds. We tested the hypothesis that aldosterone stimulates angiotensin AT1 receptor, and causes vasoconstriction by increasing oxidative stress in coronary microcirculation. Coronary arterioles (60-120 microm) were isolated from spontaneously hypertensive rats (SHR) and control Wistar Kyoto (WKY) rats, aged 23-26 weeks. They were cannulated, and pressurized at 60 cm H2O. Effect of aldosterone (10(-15) to 10(-6) M) on coronary arteriolar diameter was examined. Aldosterone rapidly and dose-dependently decreased coronary arteriolar diameter in WKY rats and SHR (diameter changes, 8.4+/-0.7% vs 13.9+/-0.8%, P<0.05). Aldosterone-induced vasoconstriction was enhanced by 1.6-folds in SHR compared to WKY rats (P<0.05). Mineralocorticoid receptor antagonist spironolactone (10(-6) M) did not influence aldosterone-induced vasoconstriction. Selective angiotensin AT1 receptor blocker valsartan (10(-4) M) or candesartan (10(-7) M) abolished aldosterone-induced vasoconstriction. Similarly, superoxide dismutase (SOD, 300 U/ml), and NADPH oxidase inhibitor apocynin (10(-4) M) abolished it. Moreover, the vasoconstrictor effect of aldosterone disappeared in denuded vessels. Real-time quantitative RT-PCR revealed that angiotensin AT1 receptor mRNA level in coronary arterioles of SHR was upregulated by 1.5-folds compared to that in WKY rats (P<0.05). Aldosterone causes vasoconstriction in coronary arterioles, and this vasoconstrictor effect is enhanced by genetically defined hypertension. Aldosterone-induced vasoconstriction is mediated by angiotensin AT1 receptor presumably via oxidative stress.

Clinical evaluation of imidapril in congestive heart failure in dogs: results of the EFFIC study

OBJECTIVES

The clinical efficacy and safety of imidapril were evaluated in dogs that presented with mild to severe congestive heart failure (New York Heart Association stage II to IV) by comparing the success rate of imidapril with a positive control by a non-inferiority approach.

METHODS

This good, clinical practice compliant, multicentre study (EFFIC study) enrolled 142 client-owned dogs and was conducted in 20 locations in France, Belgium and Germany. Dogs of various breed, age and weight were included in the study. These dogs were randomised into two groups that were treated for 84 days with either the test product, imidapril, or the positive control, benazepril, and followed up in parallel over this period. Both treatments were administered at a dose of 0.25 mg/kg once a day with the possibility of doubling this dose to 0.5 mg/kg if considered necessary from a clinical point of view. In addition, concomitant treatment was given to dogs presenting with pulmonary oedema and/or ascites, supraventricular tachyarrhythmia and/or dilated cardiomyopathy. The evolution of the New York Heart Association stage and the "functional signs" score were evaluated as primary efficacy criteria.

RESULTS

The success rate in the imidapril group was 66 compared with 68 per cent in the benazepril group. Regarding safety, 35 dogs in each group experienced at least one adverse event. Nine dogs in each group experienced at least one serious adverse event. The difference between these results was not statistically significant.

CLINICAL SIGNIFICANCE

Imidapril is as efficacious and safe as the reference product, benazepril.

Neuroendocrine evaluation of cardiac disease

Current evidence favors the view that regardless of etiology, there is a predictable sequence of neuroendocrine activation that operates in most dogs and cats with progressive heart disease and that it is largely, but not entirely, independent of etiology. The natriuretic peptides and sympathetic nervous system seem to be early responders to developing cardiac and hemodynamic perturbations in both species. BNP plays a particularly prominent role in cats, possibly as a reflection of disease etiology. Shortly thereafter, plasma endothelin concentrations rise, reflecting the impact of the hemodynamic alterations on the vasculature. Endothelin and the natriuretic peptides directly suppress plasma renin release but have divergent effects on aldosterone. Activation of the tissue RAAS may operate early on to further the progression of heart failure, but evidence of plasma RAAS activation occurs comparatively late and near the time of development of overt CHF. Finally, in animals with severe CHF that are prone to hypotension,vasopressin levels may also rise, contributing to the retention of free water and congestion that is refractory to diuretics. Although oversimplified, this scenario seems to be consistent with data obtained in human, canine, and feline patients. These observations provide some impetus for evaluating ACE inhibitors in cats and beta-receptor-blocking drugs in dogs and cats. Perhaps we are also a little closer to identifying useful biochemical markers that can aid in the diagnosis of heart disease, guide therapy, and improve our understanding of the biologic processes occurring in our patients.

New insights into degenerative mitral valve disease in dogs

Degenerative mitral valve disease (DMVD) is the most common cardiac disease in dogs. Although the disease is frequently described in the veterinary literature, many aspects are still unknown or controversial. Based on recent research findings, this article addresses the etiology, pathogenesis, inheritance, diagnosis of early DMVD, diagnosis of mild decompensated heart failure, and efficacy of early medical intervention in clinically compensated dogs.

Spectral analysis of heart rate variability in dogs with mild mitral regurgitation

OBJECTIVE

To assess autonomic function in dogs with mild mitral regurgitation (MR) that did not have clinical signs of the condition.

ANIMALS

6 healthy adult Beagles.

PROCEDURE

Mild MR was experimentally induced. A 24-hour ambulatory ECG was recorded before and after induction of MR. Heart rate variability was analyzed in frequency domains by use of the ambulatory ECG. Low-frequency (LF) and high-frequency (HF) power were calculated by integrating over their frequency intervals, and the ratio of LF to HF was also calculated. Measurements of frequency domains were analyzed for 4 time periods (midnight to 6 AM, 6 AM to noon, noon to 6 PM, and 6 PM to midnight).

RESULTS

Dogs with experimentally induced MR were classified as International Small Animal Cardiac Health Council class Ia. The HF power of dogs with MR was significantly decreased between 6 AM and noon. The ratio of LF to HF in dogs with MR was significantly increased for the periods between midnight and 6 AM, 6 AM and noon, and noon and 6 PM.

CONCLUSIONS AND CLINICAL RELEVANCE

Compensatory response through autonomic modulation was observed in dogs with mild MR that did not have abnormalities, except for cardiac murmur, during clinical examination. This result suggests that treatment during the early stages of mild MR may be beneficial. Additional studies are necessary to determine whether such treatment will delay the onset of congestive heart failure and prolong survival in dogs affected with mild MR.

Effects of long-term administration of enalapril on clinical indicators of renal function in dogs with compensated mitral regurgitation

OBJECTIVE

To determine the effect of long-term administration of enalapril on renal function in dogs with severe, compensated mitral regurgitation.

DESIGN

Randomized controlled trial.

ANIMALS

139 dogs with mitral regurgitation but without overt signs of heart failure.

PROCEDURE

Dogs were randomly assigned to be treated with enalapril (0.5 mg/kg [0.23 mg/lb], PO, q 24 h) or placebo, and serum creatinine and urea nitrogen concentrations were measured at regular intervals for up to 26 months.

RESULTS

Adequate information on renal function was obtained from 132 dogs; follow-up time ranged from 0.5 to 26 months (median, 12 months). Mean serum creatinine and urea nitrogen concentrations were not significantly different between dogs receiving enalapril and dogs receiving the placebo at any time, nor were concentrations significantly different from baseline concentrations. Proportions of dogs that developed azotemia or that had a +/- 35% increase in serum creatinine or urea nitrogen concentration were also not significantly different between groups.

CONCLUSIONS

And Clinical Relevance: Results suggest that administration of enalapril for up to 2 years did not have any demonstrable adverse effects on renal function in dogs with severe, compensated mitral regurgitation.

Canine idiopathic dilated cardiomyopathy. Part II: pathophysiology and therapy

Dilated cardiomyopathy (DCM) in dogs is characterized by ventricular and atrial enlargement, and systolic and diastolic dysfunction, with congestive heart failure (CHF) often developing at some stage. With greater understanding of the impact of neuroendocrine stimulation in heart disease, the understanding of the pathophysiology for CHF has changed considerably. It is no longer considered only to be a simple haemodynamic consequence of pump dysfunction, but is now characterized as a complex clinical syndrome with release of many neurohormones, which are believed to have impact on the progression of disease. This change in our understanding of the pathophysiology of CHF has important therapeutic implications. There are strong indications, although not yet proven, that drugs designed to influence the neuroendocrine activity, such as Angiotensin Converting Enzyme (ACE) inhibitors and beta-receptors antagonists, are efficacious as adjunct therapy of heart failure attributable to DCM in dogs. The benefits of drugs designed to influence the myocardial contractile state (positive inotropes) have not been fully evaluated. However, evidence has emerged in recent years indicating that new types of positive inotropes may be beneficial in dogs with DCM. This review focuses on the neuroendocrine aspects of DCM and their possible therapeutic implications and the place for long-term inotropic support in dogs with DCM.

Stimulation of the renin-angiotensin system in cats with hypertrophic cardiomyopathy

Feline hypertrophic cardiomyopathy (HCM) is a disease of the ventricular myocardium, which may cause sudden death in cats, but neither the aetiology nor the effect on the circulation are well understood. Fourteen cats of either sex with naturally occurring HCM were studied post mortem. Their ages ranged from 9 months to 10 years with an average age of 4.9 years. Heart weights and heart weight expressed as a percentage of body weight were elevated (27.9 g and 0.65%, respectively) as compared with normal values obtained in previous studies. Myocardial disarray was evident in nine of the 14 cats and moderate to severe fibrosis was present in six animals. To evaluate the renal renin-angiotensin system, semiquantitative morphometric data were obtained by means of renin immunohistochemistry and compared with results from an earlier study of 10 healthy cats by the author. The juxtaglomerular index was 36.8% in the cats with HCM as compared with 30.6% in healthy cats. The renin-positive portion of the afferent arteriole was increased in cats affected by HCM to 86.0 microm as compared with 49.9 microm in normal cats. The increase in kidney renin values in cats with HCM may have been due to decreased blood pressure and reduced renal perfusion resulting from impaired cardiac output.

Association between exogenous atrial natriuretic peptide and hemodynamics in dogs with congestive heart failure produced by experimental mitral regurgitation

Association between exogenous atrial natriuretic peptide (ANP) and hemodynamic changes was ascertained in 3 dogs with overt congestive heart failure (CHF(+)) and 3 dogs without congestive heart failure (CHF(-)) caused by experimental mitral regurgitation (MR). The hemodynamic measurements were recorded in all dogs during and after 1 hr infusion of ANP at the rate of 0.1 (low dose), 0.5 (medium dose) and 1.0 (high dose) microg/kg/min, respectively. Heart rate, mean arterial pressure, pulmonary capillary wedge pressure (PCWP) and systemic vascular resistance decreased significantly during and after ANP infusion even with low dose in the CHF(+). Stroke volume, stroke volume index and cardiac output in the CHF(+) during and after ANP infusion showed an increasing trend as compared with the CHF(-). Double product, an indicator of myocardial oxygen consumption, significantly decreased during and after ANP administration at all doses in the CHF(+). These findings indicate that even at low dose, exogenous ANP improves cardiac performance and reduces myocardial oxygen consumption in the CHF(+), and suggest that ANP has beneficial effects in the treatment of dogs with overt congestive heart failure resulting from MR.

Hormonal response to dobutamine cardiac stress testing in a conscious canine model of early left ventricular dysfunction induced by chronic rate overload

The aims of this study were to investigate (1) hormonal activation before and during dobutamine cardiac stress testing (DST) in a canine model of early left ventricular dysfunction (ELVD) induced by rapid right ventricular pacing (RRVP) and (2) the relationship between this hormonal profile and carnitine concentrations. Before the pacing period, the 6 dogs were assigned to 2 groups according their baseline total plasma carnitine concentration. A DST was performed on each dog before activation of the pacemaker and every 3 to 4 days during development of 3 progressive stages of ELVD (stages 1, 2 and 3). Plasma atrial natriuretic factor (ANF), angiotensin II (ANG II) and endothelin-1 (ET-1) levels were measured at the start and at the end of each DST. Effects of ELVD, DST and plasma carnitine concentration on these measurements were tested. The RRVP induced a significant increase of ANF and ANG II and a non significant trend toward increase of ET-1 in all dogs. Before the pacing period, ANF remained constant during the DST in dogs with normal total plasma carnitine concentration, while it significantly decreased in dogs with low total plasma carnitine concentration. Dobutamine stress testing induced a significant decrease in ANF in all dogs in ELVD. Dobutamine infusion induced a significant increase in ANG II in all dogs before as well as during the pacing period while ET-1 was unchanged. These results suggest that investigation of the hormonal profile before and after a dobutamine challenge might provide important diagnostic information in dogs with asymptomatic or mildly symptomatic cardiac dysfunction of different origins.

Hypomagnesemia and mitral valve prolapse in Cavalier King Charles spaniels

There is a high incidence of mitral valve prolapse (MVP), an abnormal displacement of one or both mitral valve leaflets during systole, in Cavalier King Charles Spaniels (CKCS). In humans, MVP is known to be associated with a low magnesium status. In this study, the plasma magnesium concentration was measured in 30 CKCS without heart failure. It was also investigated whether MVP-severity and degree of regurgitation correlated with plasma magnesium and a number of parameters of the renin-angiotensin system, and whether 4 weeks magnesium supplementation affected plasma magnesium or the high renin/low aldosterone profile associated with MVP. A high prevalence of hypomagnesemia was observed: plasma concentrations < 0.70 mmol/l were found in 15 dogs (50%) before and in 12 dogs (40%) after 4 weeks magnesium supplementation. The mean plasma level was 0.69 +/- 0.07 mmol/l before and 0.71 +/- 0.07 mmol/l after magnesium (P = 0.22). Plasma magnesium concentrations did not correlate with MVP-severity and degree of regurgitation. Plasma aldosterone levels correlated negatively with MVP-severity and positively with the degree of regurgitation, and serum angiotensin-converting enzyme activities correlated negatively with the degree of regurgitation. Magnesium supplementation had no effects on renin and aldosterone nor on the ratio between the two. In conclusion, many CKCS without heart failure have hypomagnesemia whether they are fed supplementary magnesium or not--a finding which may be associated with the high prevalence of MVP in this breed. Further studies, however, are needed to clarify the role of a low magnesium status in canine MVP.

Fluid therapy in the cardiac patient

Correcting fluid deficits and preventing fluid overload in patients with cardiac disease can be challenging. The purpose of the fluid therapy, the projected duration of the therapy, and the type of heart disease affecting the patient play important roles in the decision-making process. In addition, the distinction between patients who are not symptomatic (NYHA Class I) and those who are symptomatic (NYHA Classes II to IV) for their cardiac disease should be made early in fluid therapy planning.

Effects of mild mitral valve insufficiency, sodium intake, and place of blood sampling on the renin-angiotensin system in dogs

In 23 Cavalier King Charles Spaniels, 12 with mild mitral valve insufficiency (MVI) and 11 controls, the activity of the renin-angiotensin system (RAS) was assessed by measuring the plasma renin activity (PRA) and plasma aldosterone concentration (PAC) in 5 different settings. The dogs were sampled at the clinic before the trial and thereafter at home and at the clinic; during both a period on control diet and a period on low sodium diet. The dogs with mild MVI had the highest median PRA and PAC in all 5 settings. An analysis of variance accordingly showed that dogs with mild MVI had significantly higher PRA (p < 0.0001) and PAC (p = 0.03) than controls, and that the sodium intake and place of blood sampling did not significantly affect this finding. The sodium intake had highly significant effects on PRA and PAC, and the place of blood sampling had no significant effects on PRA and PAC. The activity of angiotensin-converting enzyme in serum was lower in dogs with mild MVI than in controls (p = 0.0002). The plasma levels of endothelin-1, atrial natriuretic peptide, and arginine vasopressin, 3 peptides of pathophysiologic importance in congestive heart failure, were not significantly changed by the disease. The early activation of the RAS in dogs with MVI suggests that the valvular disease process itself might be the cause of the activation, but confirmation of this requires further studies.

Breed differences in the plasma renin activity and plasma aldosterone concentration of dogs

Plasma renin activity (PRA) and plasma aldosterone concentration (PAC) were studied in 90 clinically healthy dogs: 15 Beagles, 15 Cavalier King Charles spaniels (CKCS), 15 Medium Sized Poodles, 15 Labrador retrievers, 15 Irish wolfhounds and 15 Newfoundlands. All dogs were fed a low sodium diet for at least 3 days before blood sampling in a home setting. There was a significant difference between breeds with respect to both PRA (P = 0.0002), PAC (P = 0.002) and PRA/PAC ratio (P < 0.0001). The highest PRA values were found in CKCS and Poodles, two breeds known to be predisposed to chronic valvular disease. Five CKCS had PRA values exceeding 3.0 ng/ml/h while this was the case in only one of the remaining 75 dogs. In contrast to the high PRA values, CKCS had low PAC values, and therefore much higher PRA/PAC ratios than the other breeds. In Irish wolfhounds, both the PRA and PAC values were low. In conclusion, considerable breed differences in PRA and PAC were found in the present study. Further studies are needed to determine if there is an association between developing chronic valvular disease and a high PRA in dogs.

Activation of the renin-angiotensin system in dogs with asymptomatic and symptomatic dilated cardiomyopathy

Plasma renin activity (PRA) and plasma aldosterone concentration (PAC) were assessed in 23 dogs, nine of which had asymptomatic dilated cardiomyopathy (DCM) (New York Heart Association [NYHA] class I), eight had symptomatic DCM (NYHA class III) and six had severe congestive heart failure due to DCM (NYHA class IV). None of the dogs had received any drugs before the study. PRA was increased in dogs with DCM (NYHA classes III and IV) (median values 3.8 and 30.8 ng ml-1 hour-1) compared with normal dogs (median 0.89 ng ml-1 hour-1). However, PRA was only marginally increased in dogs with DCM NYHA class I (P = 0.06). The PAC was also increased in dogs with DCM (NYHA classes III and IV) (median values 123 and 600 pg ml-1) compared with normal dogs (median 61 pg ml-1). The PAC was not significantly increased in the early stage of DCM (NYHA class I). It was concluded that in dogs with DCM, the activity of the renin-angiotensin system (RAS) was increased in NYHA functional classes III and IV, and that the increase was correlated with the severity of the disease. The fact that the RAS tended to be activated in dogs with asymptomatic DCM supports the rationale of early therapeutic intervention with inhibitors of the angiotensin-converting enzyme (ACE) as first line therapy in congestive heart failure.