Recipient Organization
NORTH CAROLINA STATE UNIV
(N/A)
RALEIGH,NC 27695
Performing Department
College of Vet Medicine
Non Technical Summary
Activation of the renin angiotensin aldosterone system (RAAS) helps to maintain blood pressure when cardiac function is decreased. However, the RAAS also results in increased afterload and myocardial energy expenditure, which eventually contribute to myocardial cell death and fibrosis. Angiotensin converting enzyme (ACE) inhibitors are widely used in treatment of cardiovascular diseases and heart failure in a variety of species, as they have been shown to improve quality of life, delay the onset of clinical heart failure, and increase longevity. Their use has been limited in horses due to poor oral bioavailability, but recent studies suggest that benazapril or quinapril may be feasible ACE inhibitors for horses. The proposed study is designed to test the hypothesis that the RAAS will become activated in horses with mitral or aortic regurgitation once the left ventricle becomes enlarged, but not before. Because indicators of RAAS status (renin or ACE activity, aldosterone) are not readily available as commercial assays, the study will also test the hypothesis that cardiac troponin I (cTnI) is a useful biomarker for activation of the RAAS in horses. Normal horses and horses with cardiac murmurs due to mitral regurgitation (MR) or aortic regurgitation (AR) will be recruited from the surrounding area. Physical and cardiac ultrasound examinations will be performed on each horse in order to characterize the severity of disease (eg normal horses, horses with MR or AR with no cardicac enlargement, and horses with MR or AR with cardiac enlargement). Indicators of RAAS status (serum ACE, plasma renin activity, and plasma and urine aldosterone) will be measured in each horse by radioimmunoassay (RIA), radioenzymatic assay (REA), or enzyme-linked immunosorbent assay (ELISA). Since atrial natriuretic peptide (ANP) is likely to be increased in horses with atrial dilation, and since ANP modulates the RAAS, ANP will also be measured in these horses. Cardiac troponin I will be measured by ELISA. Concentrations of ACE, renin, aldosterone, ANP and cTnI will be compared among groups of horses defined by severity of disease by ANOVA or Kruskal Wallis ANOVA on ranks, depending on normality of data. Pearson product-moment or Spearman rank order correlations will be used to determine whether correlations exist between cTnI and any of the indicators of the RAAS (ie ACE, renin activity or aldosterone). The proposed study is expected to help define guidelines, in terms of cardiac dimensions and/or cTnI, for when to start treatment of horses with MR or AR with ACE inhibitors.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The investigator focuses on timing of the activation of the Renin Angiotensin Aldosterone System in horses with mitral or aortic regurgitation. The central hypothesis is that RAAS will be activated only after left ventricular enlargement develops. If true, this principle would provide a strong rationale for initiating treatment with an angiotensin converting enzyme inhibitor when RAAS activation is documented but not before. In human patients with cardiac compromise, ACE inhibitors delay the onset of clinical signs of heart failure, improve quality of life and improve longevity. As commercial assays for renin, aldosterone and ACE activity are not readily available, the PI will evaluate cardiac Troponin I as a marker of RAAS activity. The goal of the study is to develop guidelines for when to initiate ACE treatment in horses with MR or AR.
Project Methods
Horses will be examined on an outpatient basis at the NCSU-VTH by the PI. They will be scheduled to arrive at the clinic early to mid morning and will be weighed at the time of admission. They will be given at least 2 hours to relax after their transport before being examined. Physical examination will be performed, with special emphasis on heart rate and rhythm, mucous membrane color, capillary refill time, pulse quality at the facial and digital arteries, venous filling, and cardiac auscultation.There will be ichocardiographic examination, blood sampling, and urine sampling.AssaysPlasma renin activityPlasma renin activity will be measured in EDTA plasma using a radioenzymatic assay performed at the clinical laboratory of the Wexler Medical Center of the Ohio State University, as reported previously12. The sensitivity of this assay is 0.10 ng/ml/h.Plasma and urine aldosteronePlasma and urine aldosterone will be measured by a commercial ELISA kit (eg Enzo Aldosterone EIA Kit ADI-900-173). The sensitivity of this assay is reported to be 4.7 pg/ml.Urine creatinineUrine creatinine will be measured in the NCSU-VTH clinical pathology lab.Serum ACE activitySerum ACE activity will be measured in serum using a commercially available REA kit (ACE REA 01-RK-ACD) according to manufacturer's directions and as previously described12. The sensitivity of this assay is 2.0 u/l.Plasma cTnIPlasma cTnI will be measured by a high sensitivity ELISA kit (eg My Biosource high sensitive cardiac troponin). The reported sensitivity of this assay is 0.05 ng/ml.Plasma ANPPlasma ANP will be measured by a commercial ELISA kit (eg Sigma-Aldrich RAB0385-1KT), following extraction from the plasma with C18 columns. The reported sensitivity of this assay is 1.02 pg/ml.Statistical AnalysisFor comparison purposes, data will be divided and analyzed in two or three ways.Analysis #1: Horses will be assigned to one of 3 groups based on echocardiography:NormalMitral Regurgitation (MR)Aortic Regurgitation (AR)Analysis #2: Horses will be assigned to one of 3 groups based on echocardiography:Normal HorsesMR or AR Horses with no Cardiac EnlargementMR or AR Horses with either LV or LA Dilatation or BothAnalysis #3: Depending on the number of horses in each of the groups in analysis 2, we may also look at 5 groups, based on echocardiography:Normal HorsesMR or AR Horses with no Cardiac EnlargementMR or AR Horses with LV Dilatation OnlyMR or AR Horses with LA Dilatation OnlyMR or AR with Both LV and LA DilatationPhysical exam, echocardiographic exam, and assay results will be divided into the groups described above. The statistical software product Sigmaplot /Sigmastat will be used to examine the data for normality (Shapiro-Wilk method). ANOVA will be used to determine differences in the above variables for normally distributed data. For data that is not normally distributed, the non-parametric Kruskal-Wallis ANOVA on ranks will be used. Post-hoc analyses will be performed by Dunn's method of multiple comparisons. Pearson product-moment or Spearman rank order correlations will be used to determine whether correlations exist between cTnI and any of the indicators of the RAAS (ie ACE, renin activity or aldosterone).