ORIGINAL ARTICLE

Effects of Chronic Carvedilol administration on blood Pressure Variability and target Organ injury in rats with sinoaortic Denervation

Efectos de la administración crónica de carvedilol sobre la variabilidad de la presión arterial y el daño de órgano blanco en ratas con desnervación sinoaórtica

 

JULIETA S. DEL MAURO1, YANINA SANTANDER¹, FACUNDO M. BERTERA ¹, ANDREA CARANZA¹, MARTÍN DONATO ^{MTSAC, 2}, SUSANA GORZALCZANY¹, RICARDO GELPI^{MTSAC, 2}, CARLOS TAIRA ^{1, 3}, CHRISTIAN HÖCHT^{1, 3}

MTSAC Full Member of the Argentine Society of Cardiology
1 Department of Pharmacology, School of Pharmacy and Biochemistry, Universidad de Buenos Aires,
2 Institute of Cardiovascular Pathophysiology, School of Medicine, Universidad de Buenos Aires – CONICET.
3 Institute of Pathophysiology and Clinical Biochemistry, School of Pharmacy and Biochemistry, Universidad de Buenos Aires

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ABSTRACT

background: Increased blood pressure variability is a novel risk factor for the development of target organ injury both in hyperten-sive and normotensive subjects, so its reduction should be considered as a new therapeutic goal.
Objective: The aim of this study was to evaluate the effect of long-term oral carvedilol treatment on blood pressure, blood pressure variability and target organ injury in the left ventricle and thoracic aorta in a model of blood pressure liability.
Methods: Twelve male Wistar rats submitted to sinoaortic denervation were treated during 8 weeks with a single dose of carvedilol 30 mg/kg or vehicle. At the end of treatment, echocardiographic evaluation and blood pressure and short-term variability measure-ments were performed. Left ventricular and thoracic aortic weights were determined and histological samples were prepared from both tissues. Metalloproteinase MMP-2 and transforming growth factor β (TGF-β) were quantified in the left ventricle and thoracic aorta.
results: Carvedilol reduced systolic blood pressure and its variability in sinoaortic-denervated rats compared with the control group (126±5 vs. 142±11 mmHg, p<0.05; SD: 2.9±0.5 vs. 6.0±0.5 mmHg; p<0.05). A lower amount of connective tissue was found in carvedilol-treated animals. The expression of TGF-β decreased in both organs after carvedilol treatment.
Conclusions: Chronic carvedilol treatment significantly reduces systolic blood pressure and its short-term variability in sinoaortic-denervated rats, decreasing the degree of left ventricular fibrosis.

Key words: Carvedilol - Target Organ Injury - Sinoaortic Denervation - Blood Pressure Variability - Ventricular Hypertrophy

RESUMEN

introducción: El incremento en la variabilidad de la presión arterial resulta un nuevo factor de riesgo para el desarrollo de daño de órgano blanco en individuos tanto hipertensos como normotensos, por lo que se postula que su reducción debe considerarse una posible nueva meta terapéutica.
Objetivos: Evaluar el efecto del tratamiento a largo plazo con carvedilol sobre la presión arterial, su variabilidad y el daño de órgano blanco en el ventrículo izquierdo y la aorta torácica en el modelo de la labilidad de presión.
Material y métodos: Se incluyeron 12 ratas Wistar macho sometidas a desnervación sinoaórtica, las cuales fueron tratadas durante 8 semanas con una única administración diaria de carvedilol 30 mg/kg o vehículo. Finalizado el tratamiento se realizó la medición de la presión arterial y de la variabilidad a corto plazo y la evaluación ecocardiográfica. Se determinó el peso del ventrículo y de la aorta torácica y se realizaron preparados histológicos sobre ambos tejidos. Se cuantificó la expresión de metaloproteinasa 2 (MMP-2) y factor de crecimiento transformante β (TGF-β) en el ventrículo izquierdo y la aorta torácica.
resultados: El carvedilol redujo la presión arterial sistólica y su variabilidad en las ratas con desnervación sinoaórtica en comparación con el grupo control (126 ± 5 vs. 142 ± 11 mm Hg, p < 0,05; DE: 2,9 ± 0,5 vs. 6,0 ± 0,5 mm Hg; p < 0,05). Se evidenció menor cantidad de tejido conectivo en los animales tratados con carvedilol. La expresión de TGF-β se encuentra disminuida en ambos órganos luego del tratamiento con carvedilol.
Conclusiones: El tratamiento crónico con carvedilol reduce significativamente la presión arterial y su variabilidad a corto plazo en ratas con desnervación sinoaórtica, disminuyendo el grado de fibrosis del ventrículo izquierdo.

Palabras clave: Carvedilol - Daño de órgano blanco - Desnervación sinoaórtica - Variabilidad de la presión arterial - Hipertrofia ventricular

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BP Blood pressure
BPV Blood pressure variability
HF High frequency
LF Low frequency
MAP Mean arterial pressure
MMP-2 Matrix metalloproteinase MMP-2
SAD Sinoaortic denervation
SBP Systolic blood pressure
TGF-β Transforming growth factor beta
VLF Very low frequency

 

INTRODUCTION

Blood pressure (BP) is not a constant variable, as it presents short-term (from minutes to days) and long-term (months) periods of deep and spontaneous oscillations. (1) The increase in blood pressure variability (BPV) has been established as a risk factor for the development of target organ injury not only in hyper-tensive patients but also in normotensive subjects. (1, 2) Clinical studies have determined that 24-hour, day-to-day and between medical visits increased BP fluctuations are associated with higher risk of major cardiovascular events in the hypertensive population. (3) Taking into account this association, it is now pos-tulated that the reduction in BPV should be regarded as a new therapeutic goal of antihypertensive therapy. (3)

Beta-blockers, which until recently had been con-sidered as first line therapy in hypertensive patients without concomitant diseases, are no longer recom-mended for the initial treatment in uncomplicated hypertensive patients due to their lower protection of cerebrovascular events and higher risk of meta-bolic disorders. (4) One of the possible reasons asso-ciated to beta-blocker reduced target organ protec-tion is the lower attenuation of BPV compared with other antihypertensive agents, especially calcium blockers. (5) However, the clinical evidence associat-ing use of beta-blockers with reduced cardiovascular protection of the hypertensive patient is based to a great extent on clinical studies evaluation atenolol, a beta-blocker with relatively low cardioselectivity and no vasodilator effect. (3, 4) In the last decades, third-generation vasodilating beta-blockers have been developed, among them carvedilol and nebivolol, with better pharmacological properties than atenolol, including the ability to reduce central BP and with neutral metabolic profile. (4) However, the superiority of third-generation vasodilating beta-blockers over at-enolol for the reduction of BPV has not been assessed in clinical studies. In a previous work performed in rats submitted to sinoaortic denervation, a model of BP liability, we showed that acute administration of carvedilol and nebivolol reduces short-term BPV to a greater extent than atenolol. (6)

Thus, the purpose of this study was to analyze the effects of chronic carvedilol administration on BP and its variability in SAD rats and its possible impact on target organ injury at the left ventricular and aortic levels.

METHODS

Male Wistar rats (200-220 g) were used. They were submit-ted to sinoaortic denervation using the Krieger method consisting in sectioning the aortic nerves at the carotid artery level and the bilateral dissection of carotid bifurcations to remove the carotid nerves. (6) Animáis were treated during 8 weeks with carvedilol 30 mg/kg (n=6) or vehicle (n=6), administered orally through a trocar. During the last two weeks of treatment systolic blood pressure (SBP) was meas-ured by the indirect tail-cuff method at 1:00 PM. Mean SBP, intraday variations and interday fluctuations were estimat-ed from these measurements.

In the last week of treatment, echocardiographic measurements were performed in anesthetized rats with a combination of ketamine/xylazine using an Acusón Sequoia C512 ultrasound system, equipped with a 7-14 MHz transducer. At the end of the two-month treatment, the carotid artery was cannulated and connected, 24 hours later, to a Spectramed P23XL pressure transducer (Spectramed, Oxnard, CA, USA) coupled to a Grass 79D polygraph (Grass Instruments, Quincy MA, USA). The polygraph was connected to a digital converter (Poliview, PVA 1, Grass-Astro Med, West Warwick, RI, USA), and 2-hour BP recordings were stored and ana-lyzed with Poliview 2.3 software (Astro Med, West Warwick, RI, USA). Mean arterial pressure (MAP), heart rate, and short-term BPV from 3-minute recordings were calculated. In addition, beat-to-beat variability was evaluated from the spectral analysis of BP using Fast Fourier Transform with a Hamming window. Spectral densities were calculated in the very low frequency (VLF) (0.1-0.2 Hz), low frequency (LF) (0.2-0.7 Hz) and high frequency (HF) (0.7-2.5 Hz) ranges. Although it is well-known that LF variability is subject to modulation of neural sympathetic vascular tone, the LF/HF ratio was used as an Índex of this activity as this normalization procedure tends to reduce the effect of changes in the absolute valúes of BPV at LF. (7, 8)

After hemodynamic parameters were measured, all animáis were sacrificed by decapitation, and the thoracic aorta and left ventricle were removed to assess target organ injury. The left ventricular weight/body weight ratio and the aortic weight/length ratio were assessed using a precisión balance as morphological markers of target organ injury. (9) Presence of fibrosis was determined by left ventricular histo-pathological evaluation on 4-mm thick histological sections according to previous studies in rats with sinoaortic denervation, (9) using Sirius Red to stain collagen fibers pink.

Finally, metalloproteinase MMP-2 (MMP-2) and trans-forming growth factor p (TGF-P) expressions were assessed by Western blot as biochemical injury markers in left ventricular and thoracic aorta homogenates. The homogenates (20 \i) were run in polyacrylamide gel SDS (12%). Transfer was performed on PVDF membranes and after blocking were incubated overnight with Rabbit anti-MMP-2 (PM 63 kDa), Mouse anti-TGF-pi (PM 13 kDa) and Rabbit anti-GAPDH (PM 37 kDa) as loading control. Proteins were detected by chemiluminescence using photographic film and were quan-tified with the ImageJ program. (10)

statistical analysis

The Kolmogorov Smirnov test was used to verify normal distribution of data and variables. Data were expressed as mean±standard error of the mean. Statistical comparisons between both groups were performed with Student´s t test using GraphPad Prism version 5.02 for Windows (GraphPad Software, San Diego, California, USA). Statistical significance was defined as p<0.05.

Ethical considerations

Animal experiments were performed according to the "Guide for the Care and Use of Laboratory Animals" (NIH Publica-tion No. 85-3, revised 1985).

RESULTS

The analysis of tail-cuff BP measurements showed that chronic carvedilol treatment reduced SBP and its intraday variation without modifying SBP fluctua-tions between interday measurements (Table 1). Central BP measured in the carotid artery of cannulated SAD animals did not show significant differences in MAP between rats treated with carvedilol 30 mg/kg and those that received vehicle (Table 1). However, chronic carvedilol treatment reduced short-term BPV evidenced by a significant reduction of standard de-viation compared with the control group (Table 1). Spectral analysis evaluation of BP recordings estab-lished that chronic treatment with carvedilol produces a highly significant reduction of beat-to beat BPV in all the frequency domains compared with the control group (Figure 1). Moreover, the LF/HF index, a marker of sympathetic vascular tone, was lower in SAD rats receiving carvedilol 30 mg/kg compared with animals treated with vehicle.

Target organ injury in the left ventricle and tho-racic aorta was different in SAD animals treated with carvedilol or vehicle. The left ventricular weight/body weight ratio was similar in the group of SAD rats re-ceiving vehicle (2.29±0.04, n=6) and those treated with carvedilol 30 mg/kg (2.47±0.12, n=6). Also, no significant differences were detected in the thoracic aorta weight/length ratio between animals treated with carvedilol (2.55±0.35 mg/mm, n=6) and the control group (3.07±0.21 mg/mm, n=6).

Echocardiographic evaluation did not reveal sig-nificant differences in the main echocardiographic systolic and diastolic function parameters between SAD rats treated with carvedilol and the control group treated with vehicle (Table 2).

Preliminary analysis of histological sections evi-denced lower degree of interstitial and perivascular fibrosis in the left ventricle of SAD rats with chronic carvedilol treatment compared with the SAD control group receiving vehicle (Figure 2). Finally, the ex-pression of molecular markers of fibrosis established that chronic treatment of SAD rats with carvedilol 30 mg/kg reduces TGF-β expression both in the left ventricle as in the thoracic aorta compared with the control group treated with vehicle (Figures 3 and 4). Conversely, no significant differences were detected in MMP-2 expression in both tissues between carvedilol and control groups

Table 1. Hemodynamic parameters of sinoaortic-denervated rats chronically treated with carvedilol or vehicle.

Hemodynamic parameter	Vehicle SAD rats (n=6)	Carvedilol SAD rats (n=6)
Indirect blood pressure (tai I cuff) SBP, mmHg	142±5	126±2 *
Intraday SD, mmHg	6.0±0.2	2.9±0.2 *
Interday SD, mmHg	7.3±0.9	7.0±1.3
Direct blood pressure in trie carotid artery MAP, mmHg	106±6	93±8
SD, mmHg	9.2±0.7	5.8±1.3 *
Percent coeffc¡ent of variation	8.7±1.0	6.2±0.5*

Data are expressed as mean±standard error of the mean. * p<0.05 vs. vehicle SAD rats. SAD: Sinoaortic denervation. SBP: Systolic blood pres-sure. SD: Standard deviation. MAP: Mean arterial pressure.

 

 

DISCUSSION

The present study shows that chronic oral treatment with the third-generation vasodilating beta-blocker carvedilol significantly reduces short-term BPV in SAD rats. However, in the carvedilol group, this in-dependent cardiovascular risk marker is only associ-ated with reduction of myocardial fibrosis without changes in morphological measurements and echo-cardiographic parameters with respect to the vehicle-treated group.

Compared to spontaneously hypertensive SAD rats (SHR-SAD), sinoaortic denervation in normoten-sive animals represents the ideal experimental model to evaluate only the importance of BPV regulation in the reduction of cardiovascular events and target or-gan injury. (3) Bilateral resection of carotid nerves in-creases BP liability without highly significant changes in average BP values. (11) However, previous studies have detected an increase in SBP by the tail-cuff ple-thysmography method. (11) In addition to hemody-namic changes, elevated BPV in SAD animals is as-sociated with increased target organ injury, including late left ventricular hypertrophy, increased fibrosis and myocardial wall thickening, aortic hypertrophy

table 2. Main echocardiographic parameters in sinoaortic-de-nervated rats after 8-week treatment with vehicle or carvedilol 30 mg/kg.
Echocardiographic páramete!	Vehicle SAD rats (n=6)	Carvedilol SAD rats (n=6)
End-d¡astol¡c díameter, mm	7.57±0.33	7.30±0.20
End-systol¡c díameter, mm	5.37±0.37	5.35±0.15
Ejectíon fractíon (%)	64.4±2.8	60.6±1.3
isovolumic relaxation time, mseg	34.7±2.0	34.5±2.5

Data are expressed as mean±SEM. Non-signifcant p for carvedilol SAD rats vs. vehicle SAD rats.

with collagen accumulation, impaired arterial disten-sibility and increased mesangial matrix. (3)

Preclinical evidence in SAD animals and clinical studies in hypertensive patients have led to postu-late that increased BPV independently contributes to target organ injury associated with hypertension. (3) It has even been suggested that the poor cardio-protective effect of beta-blockers compared with other antihypertensive drugs would be partly due to their neutral effect on BPV as opposed to the reduction de-tected with other agents, especially dihydropyridine calcium blockers. (3, 5) In this context, it is necessary to emphasize that the main evidence of the neutral or negative beta-blocker effect on BPV comes from studies evaluating atenolol. It is uncertain whether lack of attenuation of this cardiovascular risk factor with atenolol could be extended to vasodilating beta-blockers as carvedilol. In previous studies in SAD rats, we have reported that acute carvedilol administration produces a greater reduction of short-term BPV than atenolol. (6) Taking into account these studies, we compared chronic carvedilol treatment or vehicle on BPV and target organ injury in SAD rats. The analy-sis of direct and indirect BP measurements showed that a daily single dose of carvedilol 30 mg/kg can significantly reduce the standard deviation of BP re-cordings, a well-known parameter of short-term vari-ability. Moreover, as indirect interday BP variation did not differ between the carvedilol and vehicle groups, it can be inferred that the vasodilator beta-blocker did not have a significant effect on day-to-day BPV.

 

Fig. 2. Representative images (20×) of left ventricular Sirius Red staining, showing interstitial and perivascular fibrosis.

 

Fig. 3. Transforming growth factor (3 (TGF-|3) expression in left ventricular homogenates of sinoaortic-denervated rats after 8-week treatment with vehicle (light bars) or carvedilol (Carve) 30 mg/kg (dark bars). * p<0.05 vs. vehicle-treated group. GAP-DH: Glyceraldehyde-3-phosphate dehydrogenase.

Fig. 4. Transforming growth factor β (TGF-β) expression in tho-racic aorta homogenates of sinoaortic-denervated rats after 8-week treatment with vehicle (light bars) or carvedilol (Carve) 30 mg/kg (dark bars). * p<0.05 vs. vehicle-treated group. GAP-DH: Glyceraldehyde-3-phosphate dehydrogenase.

The study showed mixed results on target organ injury. Carvedilol did not reduce left ventricular and thoracic aorta morphometric hypertrophy markers or echocardiographic parameters compared with the vehicle group. However, the analysis of left ventricular histological samples and the level of TGF-β expression showed that chronic carvedilol therapy is able to reduce the degree of myocardial and vascular fibrosis in SAD rats. Lack of carvedilol efficacy on morphometric markers could be explained by late left ventricular hy-pertrophy developing only after 10-16 weeks following SAD. (13)

CONCLUSIONS

In conclusion, chronic carvedilol administration is ef-fective to reduce beat-to-beat and short-term BPV in an experimental model of BP liability. Although BPV attenuation in carvedilol-treated SAD animals did not have beneficial effects on ventricular hypertrophy markers and systolic and diastolic functional parameters, the vasodilating beta-blocker prevented, at least partially, myocardial fibrosis and TGF-β profibrotic factor expression.

acknowledgements

This work was supported by scholarships from the Scientific and Technical Secretary, Universidad de Buenos Aires, Argentina. Andrea Carranza, Martín Donato, Ricardo Gelpi y Carlos A Taira are CONICET researchers.

Conficts of interest

None declared

(See author´s conflicts of interest forms in the web / Supple-mentary Material)

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