Altered Renal Vascular Responsiveness to Vasoactive Agents in Rats with Angiotensin II-Dependent Hypertension and Congestive Heart Failure

Renal sympathetic denervation improves pressure-natriuresis relationship in cardiorenal syndrome: insight from studies with Ren-2 transgenic hypertensive rats with volume overload induced using aorto-caval fistula

The aim was to evaluate the effects of renal denervation (RDN) on autoregulation of renal hemodynamics and the pressure-natriuresis relationship in Ren-2 transgenic rats (TGR) with aorto-caval fistula (ACF)-induced heart failure (HF). RDN was performed one week after creation of ACF or sham-operation. Animals were prepared for evaluation of autoregulatory capacity of renal blood flow (RBF) and glomerular filtration rate (GFR), and of the pressure-natriuresis characteristics after stepwise changes in renal arterial pressure (RAP) induced by aortic clamping. Their basal values of blood pressure and renal function were significantly lower than with innervated sham-operated TGR (p < 0.05 in all cases): mean arterial pressure (MAP) (115 ± 2 vs. 160 ± 3 mmHg), RBF (6.91 ± 0.33 vs. 10.87 ± 0.38 ml.min-1.g-1), urine flow (UF) (11.3 ± 1.79 vs. 43.17 ± 3.24 µl.min-1.g-1) and absolute sodium excretion (UNaV) (1.08 ± 0.27 vs, 6.38 ± 0.76 µmol.min-1.g-1). After denervation ACF TGR showed improved autoregulation of RBF: at lowest RAP level (80 mmHg) the value was higher than in innervated ACF TGR (6.92 ± 0.26 vs. 4.54 ± 0.22 ml.min-1.g-1, p < 0.05). Also, the pressure-natriuresis relationship was markedly improved after RDN: at the RAP of 80 mmHg UF equaled 4.31 ± 0.99 vs. 0.26 ± 0.09 µl.min-1.g-1 recorded in innervated ACF TGR, UNaV was 0.31 ± 0.05 vs. 0.04 ± 0.01 µmol min-1.g-1 (p < 0.05 in all cases). In conclusion, in our model of hypertensive rat with ACF-induced HF, RDN improved autoregulatory capacity of RBF and the pressure-natriuresis relationship when measured at the stage of HF decompensation.

Impaired renal autoregulation and pressure-natriuresis: any role in the development of heart failure in normotensive and angiotensin II-dependent hypertensive rats?

The aim of the present study was to assess the autoregulatory capacity of renal blood flow (RBF) and of the pressure-natriuresis characteristics in the early phase of heart failure (HF) in rats, normotensive and with angiotensin II (ANG II)-dependent hypertension. Ren-2 transgenic rats (TGR) were employed as a model of ANG II-dependent hypertension. HF was induced by creating the aorto-caval fistula (ACF). One week after ACF creation or sham-operation, the animals were prepared for studies evaluating in vivo RBF autoregulatory capacity and the pressure-natriuresis characteristics after stepwise changes in renal arterial pressure (RAP) induced by aortic clamping. In ACF TGR the basal mean arterial pressure, RBF, urine flow (UF), and absolute sodium excretion (UNaV) were all significantly lower tha n in sham-operated TGR. In the latter, reductions in renal arterial pressure (RAP) significantly decreased RBF whereas in ACF TGR they did not change. Stepwise reductions in RAP resulted in marked decreases in UF and UNaV in sham-operated as well as in ACF TGR, however, these decreases were significantly greater in the former. Our data show that compared with sham-operated TGR, ACF TGR displayed well-maintained RBF autoregulatory capacity and improved slope of the pressure-natriuresis relationship. Thus, even though in the very early HF stage renal dysfunction was demonstrable, in the HF model of ANG II-dependent hypertensive rat such dysfunction and the subsequent HF decompensation cannot be simply ascribed to impaired renal autoregulation and pressure-natriuresis relationship.

Anti-Fibrotic Potential of Angiotensin (1-7) in Hemodynamically Overloaded Rat Heart

The extracellular matrix (ECM) is a highly dynamic structure controlling the proper functioning of heart muscle. ECM remodeling with enhanced collagen deposition due to hemodynamic overload impairs cardiomyocyte adhesion and electrical coupling that contributes to cardiac mechanical dysfunction and arrhythmias. We aimed to explore ECM and connexin-43 (Cx43) signaling pathways in hemodynamically overloaded rat heart as well as the possible implication of angiotensin (1-7) (Ang (1-7)) to prevent/attenuate adverse myocardial remodeling. Male 8-week-old, normotensive Hannover Spraque-Dawley rats (HSD), hypertensive (mRen-2)27 transgenic rats (TGR) and Ang (1-7) transgenic rats (TGR(A1-7)3292) underwent aortocaval fistula (ACF) to produce volume overload. Five weeks later, biometric and heart tissue analyses were performed. Cardiac hypertrophy in response to volume overload was significantly less pronounced in TGR(A1-7)3292 compared to HSD rats. Moreover, a marker of fibrosis hydroxyproline was increased in both ventricles of volume-overloaded TGR while it was reduced in the Ang (1-7) right heart ventricle. The protein level and activity of MMP-2 were reduced in both ventricles of volume-overloaded TGR/TGR(A1-7)3292 compared to HSD. SMAD2/3 protein levels were decreased in the right ventricle of TGR(A1-7)3292 compared to HSD/TGR in response to volume overload. In parallel, Cx43 and pCx43 implicated in electrical coupling were increased in TGR(A1-7)3292 versus HSD/TGR. It can be concluded that Ang (1-7) exhibits cardio-protective and anti-fibrotic potential in conditions of cardiac volume overload.

Endothelin type A receptor blockade increases renoprotection in congestive heart failure combined with chronic kidney disease: Studies in 5/6 nephrectomized rats with aorto-caval fistula

BACKGROUND

Association of congestive heart failure (CHF) and chronic kidney disease (CKD) worsens the patient's prognosis and results in poor survival rate. The aim of this study was to examine if addition of endothelin type A (ET_A) receptor antagonist to the angiotensin-converting enzyme inhibitor (ACEi) will bring additional beneficial effects in experimental rats.

METHODS

CKD was induced by 5/6 renal mass reduction (5/6 NX) and CHF was elicited by volume overload achieved by creation of aorto-caval fistula (ACF). The follow-up was 24 weeks after the first intervention (5/6 NX). The treatment regimens were initiated 6 weeks after 5/6 NX and 2 weeks after ACF creation.

RESULTS

The final survival in untreated group was 15%. The treatment with ET_A receptor antagonist alone or ACEi alone and the combined treatment improved the survival rate to 64%, 71% and 75%, respectively, however, the difference between the combination and either single treatment regimen was not significant. The combined treatment exerted best renoprotection, causing additional reduction in albuminuria and reducing renal glomerular and tubulointerstitial injury as compared with ACE inhibition alone.

CONCLUSIONS

Our results show that treatment with ET_A receptor antagonist attenuates the CKD- and CHF-related mortality, and addition of ET_A receptor antagonist to the standard blockade of RAS by ACEi exhibits additional renoprotective actions.

Endothelin type A receptor blockade attenuates aorto-caval fistula-induced heart failure in rats with angiotensin II-dependent hypertension

OBJECTIVE

Evaluation of the effect of endothelin type A (ET A ) receptor blockade on the course of volume-overload heart failure in rats with angiotensin II-dependent hypertension.

METHODS

Ren-2 renin transgenic rats (TGR) were used as a model of hypertension. Heart failure was induced by creating an aorto-caval fistula (ACF). Selective ET A receptor blockade was achieved by atrasentan. For comparison, other rat groups received trandolapril, an angiotensin-converting enzyme inhibitor (ACEi). Animals first underwent ACF creation and 2 weeks later the treatment with atrasentan or trandolapril, alone or combined, was applied; the follow-up period was 20 weeks.

RESULTS

Eighteen days after creating ACF, untreated TGR began to die, and none was alive by day 79. Both atrasentan and trandolapril treatment improved the survival rate, ultimately to 56% (18 of 31 animals) and 69% (22 of 32 animals), respectively. Combined ACEi and ET A receptor blockade improved the final survival rate to 52% (17 of 33 animals). The effects of the three treatment regimens on the survival rate did not significantly differ. All three treatment regimens suppressed the development of cardiac hypertrophy and lung congestion, decreased left ventricle (LV) end-diastolic volume and LV end-diastolic pressure, and improved LV systolic contractility in ACF TGR as compared with their untreated counterparts.

CONCLUSION

The treatment with ET A receptor antagonist delays the onset of decompensation of volume-overload heart failure and improves the survival rate in hypertensive TGR with ACF-induced heart failure. However, the addition of ET A receptor blockade did not enhance the beneficial effects beyond those obtained with standard treatment with ACEi alone.

Effect of inflammation on cytochrome P450-mediated arachidonic acid metabolism and the consequences on cardiac hypertrophy

The incidence of heart failure (HF) is generally preceded by cardiac hypertrophy (CH), which is the enlargement of cardiac myocytes in response to stress. During CH, the metabolism of arachidonic acid (AA), which is present in the cell membrane phospholipids, is modulated. Metabolism of AA gives rise to hydroxyeicosatetraenoic acids (HETEs) and epoxyeicosatrienoic acids (EETs) via cytochrome P450 (CYP) ω-hydroxylases and CYP epoxygenases, respectively. A plethora of studies demonstrated the involvement of CYP-mediated AA metabolites in the pathogenesis of CH. Also, inflammation is known to be a characteristic hallmark of CH. In this review, our aim is to highlight the impact of inflammation on CYP-derived AA metabolites and CH. Inflammation is shown to modulate the expression of various CYP ω-hydroxylases and CYP epoxygenases and their respective metabolites in the heart. In general, HETEs such as 20-HETE and mid-chain HETEs are pro-inflammatory, while EETs are characterized by their anti-inflammatory and cardioprotective properties. Several mechanisms are implicated in inflammation-induced CH, including the modulation of NF-κB and MAPK. This review demonstrated the inflammatory modulation of cardiac CYPs and their metabolites in the context of CH and the anti-inflammatory strategies that can be employed in the treatment of CH and HF.

Effects of Renal Denervation on the Enhanced Renal Vascular Responsiveness to Angiotensin II in High-Output Heart Failure: Angiotensin II Receptor Binding Assessment and Functional Studies in Ren-2 Transgenic Hypertensive Rats

Detailed mechanism(s) of the beneficial effects of renal denervation (RDN) on the course of heart failure (HF) remain unclear. The study aimed to evaluate renal vascular responsiveness to angiotensin II (ANG II) and to characterize ANG II type 1 (AT₁) and type 2 (AT₂) receptors in the kidney of Ren-2 transgenic rats (TGR), a model of ANG II-dependent hypertension. HF was induced by volume overload using aorto-caval fistula (ACF). The studies were performed two weeks after RDN (three weeks after the creation of ACF), i.e., when non-denervated ACF TGR enter the decompensation phase of HF whereas those after RDN are still in the compensation phase. We found that ACF TGR showed lower renal blood flow (RBF) and its exaggerated response to intrarenal ANG II (8 ng); RDN further augmented this responsiveness. We found that all ANG II receptors in the kidney cortex were of the AT₁ subtype. ANG II receptor binding characteristics in the renal cortex did not significantly differ between experimental groups, hence AT₁ alterations are not responsible for renal vascular hyperresponsiveness to ANG II in ACF TGR, denervated or not. In conclusion, maintained renal AT₁ receptor binding combined with elevated ANG II levels and renal vascular hyperresponsiveness to ANG II in ACF TGR influence renal hemodynamics and tubular reabsorption and lead to renal dysfunction in the high-output HF model. Since RDN did not attenuate the RBF decrease and enhanced renal vascular responsiveness to ANG II, the beneficial actions of RDN on HF-related mortality are probably not dominantly mediated by renal mechanism(s).

Effects of Epoxyeicosatrienoic Acid-Enhancing Therapy on the Course of Congestive Heart Failure in Angiotensin II-Dependent Rat Hypertension: From mRNA Analysis towards Functional In Vivo Evaluation

This study evaluates the effects of chronic treatment with EET-A, an orally active epoxyeicosatrienoic acid (EETs) analog, on the course of aorto-caval fistula (ACF)-induced heart failure (HF) in Ren-2 transgenic rats (TGR), a model characterized by hypertension and augmented activity of the renin-angiotensin system (RAS). The results were compared with standard pharmacological blockade of the RAS using angiotensin-converting enzyme inhibitor (ACEi). The rationale for employing EET-A as a new treatment approach is based on our findings that apart from increased RAS activity, untreated ACF TGR also shows kidney and left ventricle (LV) tissue deficiency of EETs. Untreated ACF TGR began to die 17 days after creating ACF and were all dead by day 84. The treatment with EET-A alone or ACEi alone improved the survival rate: in 156 days after ACF creation, it was 45.5% and 59.4%, respectively. The combined treatment with EET-A and ACEi appeared to improve the final survival to 71%; however, the difference from either single treatment regimen did not reach significance. Nevertheless, our findings support the notion that targeting the cytochrome P-450-dependent epoxygenase pathway of arachidonic acid metabolism should be considered for the treatment of HF.

Effects of renal sympathetic denervation on the course of congestive heart failure combined with chronic kidney disease: Insight from studies with fawn-hooded hypertensive rats with volume overload induced using aorto-caval fistula

Background: The coincidence of congestive heart failure (CHF) and chronic kidney disease (CKD) results in poor survival rate. The aim of the study was to examine if renal denervation (RDN) would improve the survival rate in CHF induced by creation of aorto-caval fistula (ACF).Methods: Fawn-hooded hypertensive rats (FHH), a genetic model of spontaneous hypertension associated with CKD development, were used. Fawn-hooded low-pressure rats (FHL), without CKD, served as controls. RDN was performed 4 weeks after creation of ACF and the follow-up period was 10 weeks.Results: We found that intact (non-denervated) ACF FHH exhibited survival rate of 58.8% (20 out of 34 rats), significantly lower than in intact ACF FHL (81.3%, 26/32 rats). In intact ACF FHL albuminuria remained stable throughout the study, whereas in ACF FHH it increased significantly, up to a level 40-fold higher than the basal values. ACF FHL did not show increases in renal glomerular and tubulointerstitial injury as compared with FHL, while ACF FHH exhibited marked increases in kidney injury as compared with FHH. RDN did not improve the survival rate in either ACF FHL or ACF FHH and did not alter the course of albuminuria in ACF FHL. RDN attenuated the albuminuria, but did not reduce the kidney injury in ACF FHH.Conclusions: Our present results support the notion that even modest CKD increases CHF-related mortality. RDN did not attenuate CHF-dependent mortality in ACF FHH, it delayed the progressive rise in albuminuria, but it did not reduce the degree of kidney injury.

The Role of Epoxyeicosatrienoic Acids in Cardiac Remodeling

Epoxyeicosatrienoic acids (EETs) are metabolites of arachidonic acid by cytochrome P450 (CYP) epoxygenases, which include four regioisomers: 5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET. Each of them possesses beneficial effects against inflammation, fibrosis, and apoptosis, which could combat cardiovascular diseases. Numerous studies have demonstrated that elevation of EETs by overexpression of CYP2J2, inhibition of sEH, or treatment with EET analogs showed protective effects in various cardiovascular diseases, including hypertension, myocardial infarction, and heart failure. As is known to all, cardiac remodeling is the major pathogenesis of cardiovascular diseases. This review will begin with the introduction of EETs and their protective effects in cardiovascular diseases. In the following, the roles of EETs in cardiac remodeling, with a particular emphasis on myocardial hypertrophy, apoptosis, fibrosis, inflammation, and angiogenesis, will be summarized. Finally, it is suggested that upregulation of EETs is a potential therapeutic strategy for cardiovascular diseases. The EET-related drug development against cardiac remodeling is also discussed, including the overexpression of CYP2J2, inhibition of sEH, and the analogs of EET.

Low Dose Curcumin Administered in Hyaluronic Acid-Based Nanocapsules Induces Hypotensive Effect in Hypertensive Rats

Background

Vascular drug delivery becomes a promising direction in the development of novel therapeutic strategies in the treatment of cardiovascular pathologies, such as hypertension. However, targeted delivery of hydrophobic substances, with poor bioavailability, remains a challenge. Here, we described the hypotensive effects of a low dose of curcumin delivered to the vascular wall using hyaluronic acid-based nanocapsules.

Methods

The group of hypertensive TGR(m-Ren2)27 rats, was administrated respectively with the vehicle, curcumin solution or curcumin delivered using hyaluronic acid-based nanocapsules (HyC12-Cur), for 7 days each, maintaining the wash-out period between treatments. Arterial blood pressure (systolic - SBP, diastolic – DBP) and heart rate (HR) were monitored continuously using a telemetry system (Data Science International), and Mean Arterial Pressure (MAP) was calculated from SBP and DBP.

Results

In hypertensive rats, a low dose of curcumin (4.5 mg/kg) administrated in HyC12-Cur for 7 days resulted in a gradual inhibition of SBP, DBP and MAP increase without an effect on HR. At the end of HyC12-Cur – based treatment changes in SBP, DBP and MAP amounted to −2.0±0.8 mmHg, −3.9±0.7 mmHg and −3.3±0.7 mmHg, respectively. In contrast, the administration of a curcumin solution (4.5 mg/kg) did not result in a significant hypotensive effect and the animals constantly developed hypertension. Vascular delivery of capsules with curcumin was confirmed using newly developed fluorine-rich nanocapsules (HyFC10-PFOB) with a shell based on a HA derivative and similar size as HyC12-Cur. HyFC10-PFOB gave fluorine signals in rat aortas analyzed ex vivo with a ¹⁹F NMR technique after a single intragastric administration.

Conclusion

These results suggest that nanocapsules based on hyaluronic acid, the ubiquitous glycosaminoglycan of the extracellular matrix and an integral part of endothelial glycocalyx, may represent a suitable approach to deliver hydrophobic, poorly bioavailable compounds, to the vascular wall.

Renal Sympathetic Denervation Attenuates Congestive Heart Failure in Angiotensin II-Dependent Hypertension: Studies with Ren-2 Transgenic Hypertensive Rats with Aortocaval Fistula

OBJECTIVE

We examined if renal denervation (RDN) attenuates the progression of aortocaval fistula (ACF)-induced heart failure or improves renal hemodynamics in Ren-2 transgenic rats (TGR), a model of angiotensin II (ANG II)-dependent hypertension.

METHODS

Bilateral RDN was performed 1 week after creation of ACF. The animals studied were ACF TGR and sham-operated controls, and both groups were subjected to RDN or sham denervation. In separate groups, renal artery blood flow (RBF) responses were determined to intrarenal ANG II (2 and 8 ng), norepinephrine (NE) (20 and 40 ng) and acetylcholine (Ach) (10 and 40 ng) 3 weeks after ACF creation.

RESULTS

In nondenervated ACF TGR, the final survival rate was 10 versus 50% in RDN rats. RBF was significantly lower in ACF TGR than in sham-operated TGR (6.2 ± 0.3 vs. 9.7 ± 0.5 mL min-1 g-1, p < 0.05), the levels unaffected by RDN. Both doses of ANG II decreased RBF more in ACF TGR than in sham-operated TGR (-19 ± 3 vs. -9 ± 2% and -47 ± 3 vs. -22 ± 2%, p < 0.05 in both cases). RDN did not alter RBF responses to the lower dose, but increased it to the higher dose of ANG II in sham-operated as well as in ACF TGR. NE comparably decreased RBF in ACF TGR and sham-operated TGR, and RDN increased RBF responsiveness. Intrarenal Ach increased RBF significantly more in ACF TGR than in sham-operated TGR (29 ± 3 vs. 17 ± 3%, p < 0.05), the changes unaffected by RDN. ACF creation induced marked bilateral cardiac hypertrophy and lung congestion, both attenuated by RDN. In sham-operated but not in ACF TGR, RDN significantly decreased mean arterial pressure.

CONCLUSION

The results show that RDN significantly improved survival rate in ACF TGR; however, this beneficial effect was not associated with improvement of reduced RBF or with attenuation of exaggerated renal vascular responsiveness to ANG II.

Deleterious Effects of Hyperactivity of the Renin-Angiotensin System and Hypertension on the Course of Chemotherapy-Induced Heart Failure after Doxorubicin Administration: A Study in Ren-2 Transgenic Rat

Doxorubicin's (DOX) cardiotoxicity contributes to the development of chemotherapy-induced heart failure (HF) and new treatment strategies are in high demand. The aim of the present study was to characterize a DOX-induced model of HF in Ren-2 transgenic rats (TGR), those characterized by hypertension and hyperactivity of the renin-angiotensin-aldosterone system, and to compare the results with normotensive transgene-negative, Hannover Sprague-Dawley (HanSD) rats. DOX was administered for two weeks in a cumulative dose of 15 mg/kg. In HanSD rats DOX administration resulted in the development of an early phase of HF with the dominant symptom of bilateral cardiac atrophy demonstrable two weeks after the last DOX injection. In TGR, DOX caused substantial impairment of systolic function already at the end of the treatment, with further progression observed throughout the experiment. Additionally, two weeks after the termination of DOX treatment, TGR exhibited signs of HF characteristic for the transition stage between the compensated and decompensated phases of HF. In conclusion, we suggest that DOX-induced HF in TGR is a suitable model to study the pathophysiological aspects of chemotherapy-induced HF and to evaluate novel therapeutic strategies to combat this form of HF, which are urgently needed.

Enhanced sympathetic neurotransduction in the superior mesenteric artery in a rat model of heart failure: role of noradrenaline and ATP

Heart failure (HF) is associated with neurohumoral activation, which in turn leads to an increased peripheral resistance. In mesenteric vasculature, perivascular innervation plays relevant role maintaining vascular tonus and resistance. Therefore, we aimed to determine the possible alterations in superior mesenteric artery (SMA) perivascular innervation function in HF rats. HF was induced by coronary artery occlusion in male Wistar rats, and sham-operated (SO) rats were used as controls. After 12 wk, a greater vasoconstrictor response to electrical field stimulation (EFS) was observed in endothelium-intact and endothelium-denuded SMA of HF rats. Alpha-adrenoceptor antagonist phentolamine diminished this response in a higher magnitude in HF than in SO animals. However, the noradrenaline (NA) reuptake inhibitor desipramine increased EFS-induced vasoconstriction more in segments from HF rats. Besides, EFS-induced NA release was greater in HF animals, due to a higher tyrosine hydroxylase expression and activity. P2 purinoceptor antagonist suramin reduced EFS-induced vasoconstriction only in segments from SO rats, and adenosine 5'-triphosphate (ATP) release was lower in HF than in SO. Moreover, nitric oxide (NO) synthase inhibitor N^ω-nitro-L-arginine methyl ester (L-NAME) enhanced EFS-induced vasoconstriction in a similar extent in both groups. HF was not associated with changes in EFS-induced NO release or the vasodilator response to NO donor sodium nitroprusside. In conclusion, HF postmyocardial infarction enhanced noradrenergic function and diminished purinergic cotransmission in SMA and did not change nitrergic innervation. The net effect was an increased sympathetic participation on the EFS-induced vasoconstriction that could help to understand the neurotransduction involved on the control of vascular tonus in HF.NEW & NOTEWORTHY This study reinforces the pivotal role of noradrenergic innervation in the regulation of mesenteric vascular tone in a rat model of heart failure. Moreover, our results highlight the counteracting role of ATP and NA reuptake, and help to understand the signaling pathways involved on the control of vascular tonus and resistance in heart failure postmyocardial infarction.