The effects of carperitide on left atrial pressure (LAP) in dogs with mitral valve disease (mitral regurgitation, MR) have not been documented.
The effects of carperitide on left atrial pressure (LAP) in dogs with mitral valve disease (mitral regurgitation, MR) have not been documented.
The objective was to compare the short-term effects of carperitide versus furosemide on LAP and neurohumoral factors in MR dogs.
Six healthy Beagle dogs weighing 9.8–12.6 kg (2 males and 4 females; aged 3 years) were used.
Experimental, randomized, cross-over, and interventional study. Carperitide 0.1 μg/kg/min or furosemide 0.17 mg/kg/h (1 mg/kg/6 h) was administered to dogs with surgically induced MR for 6 hours, and after a 14 day wash-out period, the other drug was administered. LAP, plasma renin activity, plasma aldosterone, and echocardiographic variables were measured.
Left atrial pressure was decreased similarly after the administration of carperitide 0.1 μg/kg/min and furosemide 0.17 mg/kg/h (1 mg/kg/6 h) compared with baseline in dogs with MR (Baseline 14.75 ± 3.74 mmHg, carperitide 10.24 ± 4.97 mmHg, P < .01, furosemide 10.77 ± 5.06 mmHg, P < .05). Plasma renin activity and plasma aldosterone were significantly lower after the administration of carperitide than after the administration of furosemide (P < .05, respectively).
Carperitide significantly decreased LAP in dogs with acute MR caused by experimental chordal rupture. Carperitide can have additional benefits from the viewpoint of minimal activation of neurohumoral factors in the treatment of dogs with MR. Additional studies in dogs with spontaneous disease are warranted.
congestive heart failure
left atrial pressure
systolic blood pressure
Mitral valve disease (MVD) is the most common cardiac disease in dogs. Moreover, as many as 75% of all dogs with signs of congestive heart failure (CHF) suffer from mitral regurgitation (MR), which was caused by myxomatous degeneration of the valve leaflets, chordae tendineae, or both.[1, 2] MR increases left atrial pressure (LAP), potentially resulting in dilatation of the left atrium. Increased LAP causes pulmonary edema, which can lead to cough, dyspnea, and even death. Reduction in LAP is a desirable goal for drugs used to treat CHF in MVD.
Atrial natriuretic peptide (ANP) is a cardiac hormone secreted by atrial cells[4-10] and is responsible for the regulation of blood pressure (BP) and body fluid homeostasis.[11-14] Carperitide is a cycle peptide consisting of 28 amino acid residues called α-human ANP, which was isolated from the human atrium, identified, and synthesized by genetic combination. Studies in human trials have shown that carperitide has multiple effects such as vasodilation, water-sodium diuresis, coronary vasodilation, and inhibition the renin–angiotensin–aldosterone system (RAAS).[19, 20] These pharmacologic effects seem to be beneficial for treatment CHF. Carperitide is likely to be efficacious in dogs because the amino acid sequence of canine α-ANP is known to be completely homologous to the human α-ANP. Previous studies have reported the intravenous infusion of carperitide in normal dogs,[22-27] dogs with MR, and dogs with CHF induced by rapid right ventricular pacing.
The effect of carperitide on LAP and circulating concentrations of neurohumoral factors in conscious dogs with MR has not been fully evaluated in a quantitative manner because of difficulties in directly measuring LAP. Furosemide, a loop diuretic, has a strong diuretic effect and is used for the treatment of dogs with CHF caused by MR.[1, 2] Furosemide reduces the total circulating blood volume, which in turn reduces LAP and left ventricular filling pressure, and leads to the clinical improvement of the patients.[30-33] However, reduction in the total circulating blood volume results in activation of RAAS. We have previously used a radiotelemetry system to report the effects of angiotensin-converting enzyme (ACE) inhibitors and furosemide in conscious dogs with MR.[34-36] In this study, we used a radiotelemetry system to monitor LAP in dogs with experimentally induced MR and evaluated the effects of carperitide by echocardiography, BP analysis, and blood tests. In addition, we compared the effects of carperitide with that of furosemide.
Before the start of the study, six 3-year-old Beagle dogs (2 males and 4 females) weighing 11.1 ± 1.2 kg (range, 9.8–12.6 kg) were evaluated by general physical examination, blood and serum biochemical evaluations, electrocardiography, thoracic radiography, and echocardiography and no abnormalities were detected. All dogs did not present clinical signs, such as cough and exercise intolerance. Also, all dogs were acclimatized to the experimental environment and human handling. During all phases of the study, the dogs were managed and cared for in accordance with the standards established by the Tokyo University of Agriculture and Technology (TUAT) and described in its “Guide for the Care and Use of Laboratory Animals.” This study was approved by the Experimental Animal Committee of TUAT (acceptance no. 21-19).
Dogs were premedicated with meloxicama (0.2 mg/kg SC), atropine sulfateb (0.04 mg/kg SC), butorphanol tartratec (0.2 mg/kg IV), and midazolam hydrochlorided (0.2 mg/kg IV). Induction was achieved with propofole (4 mg/kg IV), after which the dog was intubated. General anesthesia was maintained with inhalation of isofluranef mixed with oxygen. A left lateral thoracotomy was performed at the fifth intercostal space and the pericardium was opened by standard procedures. The left atrium was purse-string sutured with 3-0 nylon and a small incision was made at the center of the purse-string suture. The suture then was loosened and 5-in. curved Halsted mosquito forceps were inserted through the small incision to grasp and rupture the mitral valvular chordae tendineae. The position of the chordae tendineae and the degree of induced MR were monitored by transesophageal echocardiography and these procedures were repeated until visible MR was identified without any manual manipulation. The telemetry transmitter catheterg then was inserted 1 cm into the small incision and the catheter was fixed to the left atrium with a suture. The telemetry transmitter body was implanted under the triceps brachii muscle and the catheter was fixed to abdominal trunk muscles with 3-0 nylon suture. The chest then was closed in layers and air was evacuated by standard procedures. Postoperatively, cefamedinh was administered (50 mg/kg/day IV or PO) for 7 days and postoperative pain was treated with meloxicam (0.1 mg/kg SC) for 3 days. Thoracic radiography and echocardiography were performed to evaluate pulmonary venous congestion and cardiac dilatation (Fig S1). Thoracic radiographic and echocardiographic examinations were performed to check for the presence of pulmonary edema and cardiac dilatation. After the radiotelemetry transmitter implantation, the dogs were rested for at least 8 weeks, until no major variations were identified in echocardiographic evaluation and LAP.
Carperitidei 0.1 μg/kg/min or furosemidej 0.17 mg/kg/h (1 mg/kg/6 h) was administered to 3 dogs for 6 hours, respectively. After a 14-day wash-out period, the other drug was administered. We used the randomized, cross-over study method for choice of the drug.
All radiotelemetry systemsk and recording procedures were the same as those described in a previous report. The maximum, mean, and minimum LAP were obtained as the averages of 10-second segments from continuous waveform recordings (Fig S2).[37, 38] LAP was measured 30 minutes before, during, and after the administration of drugs. The sampling frequency was every 10 seconds. To eliminate the effect of drinking behavior, drinking water was restricted during 6 hours of this study. Dogs were housed in individual metal cages (size: W 90 cm × D 100 cm × H 110 cm), and were not given water for 6 hours to limit water to drink.
Before and after administration of drugs, echocardiographic measurements were performed with BP and LAP measurements. A single investigator performed transthoracic conventional echocardiography as well as 2-dimensional spectral Doppler and tissue Doppler echocardiography. Each dog was positioned in left and right recumbency, with echocardiographic examinations performed by means of a digital ultrasonographic systeml with a 5.0 MHz sector transducer. Sweep speed during the Doppler and M-mode recordings was 150–200 mm/s. Right parasternal views were used to measure heart dimensions. LA/Ao was assessed in a right parasternal short-axis view of the heart base for assessing LA enlargement. The internal diameter of the aorta was measured along the commissure between the noncoronary and right coronary aortic valve cusp and internal diameter of the left atrium in a line extending from and parallel to the commissure between the noncoronary and left coronary aortic valve cusp to the distant margin of the left atrium on the 1st frame after aortic valve closure. A short-axis M-mode view at the chordal level was used to measure left ventricular internal diameter in the diastolic period (LVEDD). Left apical views of the left ventricular inflow and outflow tracts were used to measure mitral inflow and aortic flow using a pulsed wave sample volume of 4 mm. Forward stroke volume (SV) and cardiac output (CO) were calculated by use of a left ventricular outflow view. SV was calculated as SV = velocity time integral × cross-sectional area. CO was calculated as CO = SV × HR. The early diastolic myocardial velocities (Ea) by pulsed tissue Doppler imaging (TDI) were measured at lateral mitral annulus in the left apical views. Peak transmitral early diastolic wave (E wave) velocity and atrial contraction wave (A wave) were measured from Doppler signals of the mitral inflow, and E/A, E/Ea were calculated. All echocardiographic variables were averaged from 5 consecutive beats.
All indirect arterial BP recordings were obtained by the oscillometric method.m Cuff size width was set to approximately 40% of tail circumference for each dog. Five consecutive measurements were averaged for each dog for use in the calculations. Systemic vascular resistance (SVR) was calculated as SVR = 79.9 × (mean BP − CVP)/CO, and CVP was defined as 5 mmHg attributable to a lack of right-sided heart failure signs, jugular distension, or positive hepatojugular reflex.
A balloon catheter was placed in the urinary bladder of each dog. Urine samples were collected at each measurement points, before the administration of the drug, and at 30 minutes, 1, 2, 3, 4, 5, and 6 hours after administration. Baseline values were those obtained 30 minutes before drug administration. Urine volumes were calculated in terms of volume per hour.
Blood samples were collected through the jugular vein before and after the 6-hour administration of drugs. Blood samples for the measurement of the plasma renin activity and plasma aldosterone were immediately transferred to chilled disposable tubes containing EDTA (1 mg/mL), and then placed at 4°C for 30 minutes. Subsequently, plasma was separated and stored at −80°C. Plasma concentration of renin activity and aldosterone was measured at a commercial laboratory using radioimmunoassay technique. Blood urea nitrogen, creatinine, sodium, potassium, and chloride were measured with the commercially available biochemical autoanalyzer.n Baseline value was obtained before the first treatment.
All data are represented as mean plus or minus standard deviation (SD). All data were normally distributed. A 1-way repeated measures analysis of variance (ANOVA) in conjunction with a Bonferroni's multiple comparison test was used for comparing plasma hormones, biochemical blood tests, and echocardiographic variables before and 6 hours after administration of carperitide and furosemide. A 2-way repeated measures ANOVA in conjunction with a Bonferroni's multiple comparison test was used to evaluate the temporal alteration of LAP and systolic BP (SBP) after the administration of carperitide and furosemide. Statistical significance was defined as P < .05. GraphPad Prism version 5.0ao and EXCEL 2008p were used to perform these statistical analyses.
The operation to rupture the mitral valvular chordae tendineae and implant the transmitter was successful in all dogs. Mean LAP was 14.75 ± 3.75 mmHg. LVEDD was enlarged from 3.10 ± 0.11 to 3.98 ± 0.41 cm. LA/Ao was increased from 1.21 ± 0.10 to 1.61 ± 0.28. Two dogs were stage C, 4 other dogs were stage B2 based on the guidelines for the diagnosis and treatment of canine chronic valvular heart disease of the American College of Veterinary Internal Medicine. Two dogs classified as stage C were coughing occasionally because of left atrial dilatation; pulmonary edema was not present on radiography. The other dogs were asymptomatic. Clinical status of the dogs did not change during the study. No obvious adverse effects were observed during periods of carperitide and furosemide administration.
Mean LAP decreased significantly 6 hours after the administration of carperitide compared with baseline (14.75 ± 3.74 mmHg to 10.24 ± 4.97 mmHg, P < .05), as shown in Figure 1. Similarly, Mean LAP significantly decreased 6 hours after the administration of furosemide compared with baseline (15.11 ± 3.84 mmHg to 10.77 ± 5.06 mmHg, P < .05). There was no significant difference in reduction in LAP between the administration of carperitide and furosemide. Statistically significant reduction in LAP was first observed 1 hour after the administration of carperitide. In contrast, statistically significant reduction in LAP was observed 30 minutes after the administration of furosemide.
Systolic BP decreased significantly 6 hours after the administration of carperitide compared with baseline (123.9 ± 9.2 mmHg to 108.1 ± 9.8 mmHg, P < .05), as shown in Figure 2. In addition, the final SBP was lower after the administration of carperitide than after the administration of furosemide (108 ± 9.8 mmHg compared to 120.7 ± 8.4 mmHg, P < .05). Significant reduction was first observed 30 minutes after the administration of carperitide. There was no significant difference between baseline and after the administration of furosemide.
Significant increase was first observed 2 hours after the administration of carperitide and continued until 4 hours (Fig 3). In contrast, significant increase was first observed 30 minutes after the administration of furosemide and continued until 5 hours after. Total urine volume was greater after the administration of furosemide compared with carperitide (358 ± 79 mL versus 85 ± 26 mL, P < .01).
Plasma renin activity increased significantly after the administration of furosemide compared with baseline (Fig 4) (P < .01), and there was significant difference in circulating renin concentration after the administration of carperitide compared with furosemide (P < .01). Plasma aldosterone increased after the administration of furosemide compared with baseline, but not significantly (P > .05). There was significant difference in plasma aldosterone concentration after the administration of carperitide compared with furosemide (P < .05). As shown in Table 1, other variables did not change significantly.
|LA/Ao||1.61 ± 0.28||1.55 ± 0.21||1.64 ± 0.18|
|%FS||37.9 ± 4.67||39.6 ± 4.11||39.2 ± 5.57|
|LVEDD (cm)||3.98 ± 0.41||3.87 ± 0.40||3.87 ± 0.53|
|E wave (m/s)||0.95 ± 0.25||0.89 ± 0.17||0.80 ± 0.17a|
|E/A||1.71 ± 0.43||1.59 ± 0.57||1.61 ± 0.56|
|E/Ea||8.01 ± 1.20||7.25 ± 1.43a||7.11 ± 0.81a|
|SV (mL)||15.4 ± 2.57||16.0 ± 2.86b||15.2 ± 3.47|
|HR (bpm)||145.1 ± 10.4||140.9 ± 13.0||141.3 ± 16.4|
|CO (mL/min)||2,237 ± 392||2,243 ± 354||2,133 ± 349|
|SVR (dyne*s/cm5)||4,331 ± 642||3,717 ± 428a,b||4,428 ± 744|
|BUN (mg/dL)||14.0 ± 2.9||15.4 ± 3.8||18.2 ± 2.8|
|CRE (mg/dL)||0.6 ± 0.1||0.6 ± 0.1||0.7 ± 0.1|
|Sodium (mmol/L)||145 ± 5.7||146 ± 6.1||141 ± 5.6|
|Potassium (mmol/L)||4.4 ± 0.6||4.4 ± 0.5||3.8 ± 0.2|
|Chloride (mmol/L)||109 ± 6.0||110 ± 9.1||107 ± 7.1|
E wave decreased significantly after the administration of furosemide compared with baseline (Table 1) (P < .05). In addition, E/Ea decreased significantly after the administration of carperitide and furosemide compared with baseline (P < .05). There was significant difference in SVR after the administration of carperitide and furosemide (P < .05). As shown in Table 1, other variables did not change significantly.
This study demonstrated that LAP was decreased similarly with carperitide 0.1 μg/kg/min or furosemide 0.17 mg/kg/h in dogs with experimentally induced MR. Secondly, carperitide was more effective than furosemide in afterload reduction. Thirdly, furosemide was more effective than carperitide in diuretic effect. Finally, plasma renin activity and plasma aldosterone were not elevated after the administration of carperitide.
Carperitide has potent vasodilating effect and modest diuretic activities.[16, 17] As vasodilators and diuretics have been widely used to decrease LAP and treat the dogs with MR, the infusion of ANP is expected to produce beneficial effects on LAP and the dogs with MR. In humans with CHF, carperitide decreases pulmonary capillary wedge pressure (PCWP) (measured as a surrogate for LAP).[43-45] Moreover, in veterinary medicine, Asano et al showed that carperitide decreases PCWP in dogs with experimentally induced MR; however, they used only 3 dogs with heart failure and without heart failure. The sample size in this study was too small, and could be questionable from the viewpoint of statistical analysis. In addition, as general anesthesia was used during measurement of PCWP, hemodynamical alterations such as afterload may have occured. In this study, LAP was decreased after the administration of carperitide in the conscious dogs with MR (Fig 1). These results suggest that carperitide may be useful to decrease LAP in clinical cases with MR.
Estimation of reduction in LAP using echocardiography is particularly useful in the clinical situation. We previously have reported that E wave and E/Ea can be used for the evaluation of preload after administration of furosemide, and have monitored the reduction in LAP in the short term. Previous reports suggest that E/Ea is a good index for the estimation of LAP.[46-48] In this study, E/Ea decreased significantly after the administration of carperitide and furosemide (Table 1) suggesting that E/Ea may be useful for the evaluation of each drug on LAP. Conversely, other variables including LVEDD and LA/Ao did not change in this study suggesting that echocardiographic measures associated with volume loading did not decrease, even though LAP decreased in short term. SBP did not decrease and SVR was increased slightly after the administration of furosemide (Fig 3; Table 1). Moreover, RAAS was rapidly activated after the administration of furosemide. This result suggests that increased SVR reflects vasoconstriction in response to decreased blood volume.
In this study, LAP was decreased to a similar extent with carperitide 0.1 μg/kg/min or furosemide 0.17 mg/kg/h. However, the diuretic effect of carperitide was weaker than furosemide. In addition, the decreased total systemic resistance and SBP that were observed after administration of carperitide suggest that ANP dilates resistance vessels. Several studies have shown that ANP causes relaxation of various arterial and venous ring preparation.[49-51] These results suggest that infusion of carperitide alters the loading conditions on the heart by dilating both arterioles and veins, and thereby decreased LAP in the same manner as conventional vasodilators. Therefore, the reduction in LAP after carperitide administration is likely attributable to both a diuresis and vasodilation.
The RAAS has a compensatory role in the pathophysiology of CHF by elevating peripheral vascular resistance and by inducing the retention of salt and water to maintain blood flow to vital organs. Use of furosemide in dogs with CHF induces systemic vasoconstriction and stimulates neurohumoral factors such as plasma renin activity and plasma aldosterone. In human medicine, these undesirable effects seem to be inhibited when furosemide is given in conjunction with ANP. Numerous studies indicate that the administration of ANP in addition to a nitrate, furosemide, and a catecholamine in patients with complicated chronic heart failure significantly inhibited circulating levels of aldosterone. In this study, plasma renin activity and plasma aldosterone were not increased after the administration of carperitide. On the other hand, after the administration of furosemide, plasma renin activity and plasma aldosterone were increased (Fig 4). These results suggest that carperitide does not activate neurohumoral factors in dogs with MR, even though carperitide has diuretic and blood pressure–lowering effect. There is also a possibility that the minimal activation of RAAS caused by carperitide may, at least in part, be attributable to its limited diuretic effect compare to furosemide. Further study on the effects of carperitide treatment on cardiac sympathetic nerve activity, cardiac function, and hemodynamic variables in dogs with naturally occurring MR is indicated. Carperitide is unlikely to replace furosemide in the treatment of CHF; however, if the concurrent use of carperitide in dogs with CHF can reduce the quantity of furosemide needed to control clinical signs, neurohumoral factors may not be activated to some extent and prognosis may be improved.
Carperitide is used at dosage of 0.1 μg/kg/min for patients with CHF in human medicine as reference dosage. In principle, infusion was allowed up to 0.2 μg/kg/min. Carperitide decreased LAP by 0.1 μg/kg/min or more of dosage in dogs with MR, and dogs with CHF induced by rapid right ventricular pacing. Therefore, in this study, the dosage of 0.1 μg/kg/min was used. However, this study was not designed to evaluate the optimal dosage. Therefore, the optimal dosage of carperitide for dogs with MR is unknown. These study results should be extrapolated to the clinical cases carefully, although beneficial effects in human medicine were reported. In this study, adverse effects of carperitide were not observed, but we feel that this warrants further examination.
The furosemide dosage used in this study is common and clinically used (0.17 mg/kg/6 h; ie, 1 mg/kg/6 h). Furosemide has a more diuretic effect when administered by constant rate infusion than by intermittent bolus in the same dosage.[56, 57] However, there were no significant differences in patients’ global assessment of clinical signs or in the change in renal function when diuretic treatment was administered by bolus as compared with continuous infusion in human patients with acute decompensated heart failure. The dosage and route of administration could affect hormone levels and urinary volume. Therefore, because different dosages and routs may cause different results of RAAS activation and urinary volume, our results should be interpreted with caution.
In this study, six 3-year-old Beagle dogs were used and 8-week period was defined as a subchronic period for experimentally induced MR. Although 2 dogs, classified as stage C, were coughing only infrequently because of left atrial dilatation, pulmonary edema was not present on radiography. The symptom caused by the CHF was not seen in the 2 dogs. Therefore, the diuretic treatment was not necessary, and there were no abnormalities of activity, appetite, and respiratory rate during this study. Cardiac dysfunction and myocardial tissue damage of clinical cases with MR might differ from the model dogs in this study. In addition, plasma renin activity and plasma aldosterone of our model dogs were normal in this study. RAAS is activated in many cases of dogs with chronic MR. Therefore, our model may resemble more closely to acute MR and differ from naturally occurring chronic MR. SV and CO were calculated by echocardiography. Therefore, they may differ from the value strictly measured with the catheter.
Left atrial pressure was decreased similarly with carperitide 0.1 μg/kg/min or furosemide 0.17 mg/kg/h (1 mg/kg/6 h) in conscious dogs with experimentally induced MR. There were significant differences between after plasma renin activity and plasma aldosterone concentration after the administration of carperitide compared with furosemide. Therefore, carperitide may have additional benefits from the viewpoint of minimal activation of neurohumoral factors in the treatment of dogs with MR because RAAS is not activated. Additional studies are warranted in clinical patients with degenerative MVD and CHF.
We are grateful to Mitsubishi Chemical Medience Corporation for support to measure plasma renin activity and plasma aldosterone.
Conflict of Interest Declaration: Authors disclose no conflict of interest.
Metacam 0.5% injectable; Boehringer Ingelheim Vetmedica Japan, Tokyo, Japan
Atropine sulfate; Tanabe Seiyaku Co, Ltd, Osaka, Japan
Vetorphale; Meiji Seika kaisha Ltd, Tokyo, Japan
Dormicum; Astellas Pharma Inc, Tokyo, Japan
Rapinovet; Schering-Plough, Tokyo, Japan
Isoflu; Dainippon Sumitomo Pharma Co, Ltd, Osaka, Japan
TA11PA-D70; Data Sciences International, St. Paul, MN
Cefamezin; Astellas Pharma Inc
HANP for Injection; Daiichi Sankyo Co, Ltd, Tokyo, Japan
Lasix; Sanofi-Aventis K.K., Tokyo, Japan
DSI Dataquest A.R.T. 4.1; Data Sciences International, St. Paul, MN
α-10; Aloka Co, Ltd, Tokyo, Japan
BP-100D; Fukuda ME, Tokyo, Japan
DRI-CHEM 7000V; FUJIFILM Medical Co, Ltd, Tokyo, Japan
GraphPad Prism version 5.0a; GraphPad, San Diego, CA
EXCEL 2008 for Macintosh; Microsoft, Redmond, WA