The effect of atrial natriuretic peptide on human isolated resistance arteries

Cardiac and Vascular Remodeling After 6 Months of Therapy With Sacubitril/Valsartan: Mechanistic Insights From Advanced Echocardiographic Analysis

Background

Effects of Sacubitril/Valsartan (S/V) on left ventricular (LV) mechanics and ventricular-arterial coupling in patients with heart failure with reduced ejection fraction (HFrEF) are not completely understood. The aim of this study was to evaluate both cardiac and vascular remodeling in a group of HFrEF patients undergoing S/V therapy.

Methods

Fifty HFrEF patients eligible to start a therapy with S/V were enrolled. Echocardiographic evaluation was performed at baseline and after 6 months of follow-up (FU). Beside standard evaluation, including global longitudinal strain (GLS), estimated hemodynamic forces (HDFs) and non-invasive pressure-volume curves (PV loop) were assessed using dedicated softwares. HDFs were evaluated over the entire cardiac cycle, in systole and diastole, both in apex to base (A-B) and latero-septal (L-S) directions. The distribution of LV HDFs was evaluated by L-S over A-B HDFs ratio (L-S/A-B HDFs ratio). Parameters derived from estimated PV loop curves were left ventricular end-systolic elastance (E_es), arterial elastance (E_a), and ventricular-arterial coupling (VAC).

Results

At 6 months of FU indexed left ventricular end-diastolic and end-systolic volumes decreased (EDVi: 101 ± 28 mL vs. 86 ± 30 mL, p < 0.001; ESVi: 72 ± 23 mL vs. 55 ± 24 mL, p < 0.001), ejection fraction and GLS significantly improved (EF: 29 ± 6% vs. 37 ± 7%, p < 0.001; GLS: −9 ± 3% vs. −13 ± 4%, p < 0.001). A reduction of E_a (2.11 ± 0.91 mmHg/mL vs. 1.72 ± 0.44 mmHg/mL, p = 0.008) and an improvement of E_es (1.01 ± 0.37 mmHg/mL vs. 1.35 ± 0.6 mmHg/mL, p < 0.001) and VAC (2.3 ± 1.1 vs. 1.5 ± 0.7, p < 0.001) were observed. Re-alignment of HDFs occurred, with a reduction of diastolic L-S/A-B HDFs ratio [23 (20–35)% vs. 20 (11–28) %, p < 0.001].

Conclusion

S/V therapy leads to a complex phenomenon of reverse remodeling involving increased myocardial contractility, HDFs distribution improvement, and afterload reduction.

Angiotensin receptor-neprilysin inhibitors: Comprehensive review and implications in hypertension treatment

Angiotensin receptor-neprilysin inhibitors (ARNIs) are a new class of cardiovascular agents characterized by their dual action on the major regulators of the cardiovascular system, including the renin-angiotensin system (RAS) and the natriuretic peptide (NP) system. The apparent clinical benefit of one ARNI, sacubitril/valsartan, as shown in clinical trials, has positioned the drug class as a first-line therapy in patients with heart failure, particularly with reduced ejection fraction. Accumulating evidence also suggests that sacubitril/valsartan is superior to conventional RAS blockers in lowering blood pressure in patients with hypertension. To decide whether to apply an ARNI to treat hypertension clinically, it is important to understand the potential properties of the drug in modulating multiple factors inside and outside the cardiovascular system beyond its effect on reducing peripheral blood pressure. In this context, ARNIs are distinct from preexisting antihypertensive medications in terms of the multiple actions of NPs in various organs and the pharmacological potential of neprilysin inhibitors to modulate multiple cardiac and noncardiac peptides. In particular, analysis of the clinical trials of sacubitril/valsartan implies that ARNIs can provide additional clinical benefits independent of their original purpose, including alleviation of glycemic control and renal impairment in patients with heart failure. Understanding the potential mechanisms of action of ARNIs will help interpret the relevance of their additional benefits beyond lowering blood pressure in hypertension. This review summarizes the comprehensive clinical evidence and relevance of ARNIs by specifically focusing on the potential properties of this new drug class in treating patients with hypertension.

Natriuretic peptides relax human intrarenal arteries through natriuretic peptide receptor type-A recapitulated by soluble guanylyl cyclase agonists

AIM

Natriuretic peptides, BNP and ANP increase renal blood flow in experimental animals. The signalling pathway in human kidney vasculature is unknown. It was hypothesized that BNP and ANP cause endothelium-independent relaxation of human intrarenal arteries by vascular natriuretic peptide receptor-A, but not -B and -C, which is mimicked by agonists of soluble guanylyl cyclase sGC.

METHODS

Human (n = 54, diameter: 665 ± 29 µm 95% CI) and control murine intrarenal arteries (n = 83, diameter 300 ± 6 µm 95% CI) were dissected and used for force recording by four-channel wire myography. Arterial segments were pre-contracted, then subjected to increasing concentrations of BNP, ANP, phosphodiesterase 5-inhibitor sildenafil, sGC-activator BAY 60-2770 and -stimulator BAY 41-2272. Endothelial nitric oxide synthase (eNOS) dependence was examined by use of L-NAME and eNOS knockout respectively. Molecular targets (NPR A-C, sGC, phosphodiesterase-5 and neprilysin) were mapped by PCR, immunohistochemistry and RNAscope.

RESULTS

BNP, ANP, sildenafil, sGC-activation and -stimulation caused concentration-dependent relaxation of human and murine intrarenal arteries. BNP responses were independent of eNOS and were not potentiated by low concentration of phosphodiesterase-5-inhibitor, sGC-stimulator or NPR-C blocker. PCR showed NPR-A and C, phosphodiesterase-5, neprilysin and sGC mRNA in renal arteries. NPR-A mRNA and protein was observed in vascular smooth muscle and endothelial cells in arteries, podocytes, Bowmans capsule and vasa recta. NPR-C was observed in tubules, glomeruli and vasculature.

CONCLUSION

Activation of transmembrane NPR-A and soluble guanylyl cyclase relax human preglomerular arteries similarly to phosphodiestase-5 inhibition. The human renal arterial bed relaxes in response to cGMP pathway.

Effects of Sacubitril/Valsartan (LCZ696) on Natriuresis, Diuresis, Blood Pressures, and NT-proBNP in Salt-Sensitive Hypertension

Salt-sensitive hypertension (SSH) is characterized by impaired sodium excretion and subnormal vasodilatory response to salt loading. Sacubitril/valsartan (LCZ696) was hypothesized to increase natriuresis and diuresis and result in superior blood pressure control compared with valsartan in Asian patients with SSH. In this randomized, double-blind, crossover study, 72 patients with SSH received sacubitril/valsartan 400 mg and valsartan 320 mg once daily for 4 weeks each. SSH was diagnosed if the mean arterial pressure increased by ≥10% when patients switched from low (50 mmol/d) to high (320 mmol/d) sodium diet. The primary outcome was cumulative 6- and 24-hour sodium excretion after first dose administration. Compared with valsartan, sacubitril/valsartan was associated with a significant increase in natriuresis (adjusted treatment difference: 24.5 mmol/6 hours, 50.3 mmol/24 hours, both P <0.001) and diuresis (adjusted treatment difference: 291.2 mL/6 hours, P <0.001; 356.4 mL/24 hours, P =0.002) on day 1, but not on day 28, and greater reductions in office and ambulatory blood pressure on day 28. Despite morning dosing of both drugs, ambulatory blood pressure reductions were more pronounced at nighttime than at daytime or the 24-hour average. Compared with valsartan, sacubitril/valsartan significantly reduced N-terminal pro B-type natriuretic peptide levels on day 28 (adjusted treatment difference: −20%; P =0.001). Sacubitril/valsartan and valsartan were safe and well tolerated with no significant changes in body weight or serum sodium and potassium levels with either treatments. In conclusion, sacubitril/valsartan compared with valsartan was associated with short-term increases in natriuresis and diuresis, superior office and ambulatory blood pressure control, and significantly reduced N-terminal pro B-type natriuretic peptide levels in Asian patients with SSH.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01681576.

Effect of natriuretic peptides on cerebral artery blood flow in healthy volunteers

The natriuretic peptides (NPs), atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP), have vasoactive functions that concern humans and most animals, but their specific effects on cerebral circulation are poorly understood. We therefore examined the responsiveness of cerebral arteries to different doses of the natriuretic peptides in animals and humans. We conducted a dose-response experiment in guinea pigs (in vitro) and a double-blind, three-way cross-over study in healthy volunteers (in vivo). In the animal experiment, we administered cumulative doses of NPs to pre-contracted segments of cerebral arteries. In the main study, six healthy volunteers were randomly allocated to receive two intravenous doses of ANP, BNP or CNP, respectively, over 20 min on three separate study days. We recorded blood flow velocity in the middle cerebral artery (VMCA) by transcranial Doppler. In addition, we measured temporal and radial artery diameters, headache response and plasma concentrations of the NPs. In guinea pigs, ANP and BNP but not CNP showed significant dose-dependent relaxation of cerebral arteries. In healthy humans, NP infusion had no effect on mean VMCA, and we found no difference in hemodynamic responses between the NPs. Furthermore, natriuretic peptides did not affect temporal and radial artery diameters or induce headache. In conclusion, natriuretic peptides in physiological and pharmacological doses do not affect blood flow velocity in the middle cerebral artery or dilate extracerebral arteries in healthy volunteers.

Atrial natriuretic peptide and regulation of vascular function in hypertension and heart failure: implications for novel therapeutic strategies

Atrial natriuretic peptide (ANP) plays a pivotal role in modulation of vascular function and it is also involved in the pathophysiology of several cardiovascular diseases. We provide an updated overview of the current appraisal of ANP vascular effects in both animal models and humans. We describe the physiological implications of ANP vasomodulatory properties as well as the involvement of ANP, through its control of vascular function, in hypertension and heart failure. The principal molecular mechanisms underlying regulation of vascular tone, that is natriuretic peptide receptor type A/cyclic guanylate monophosphate, natriuretic peptide receptor type C, nitric oxide system, are discussed. We review the literature on therapeutic implications of ANP in hypertension and heart failure, examining the potential use of ANP analogues, neutral endopeptidase (NEP) inhibitors, ACE/NEP inhibitors, angiotensin receptor blocker (ARB)/NEP inhibitors, the new dual endothelin-converting enzyme (ECE)/NEP inhibitors and ANP-based gene therapy. The data discussed support the role of ANP in different pathological conditions through its vasomodulatory properties. They also indicate that ANP may represent an optimal therapeutic agent in cardiovascular diseases.

CNP, but not ANP or BNP, relax human isolated subcutaneous resistance arteries by an action involving cyclic GMP and BKCa channels

Natriuretic peptides play an important role in sodium regulation and blood pressure (BP) control. We examined the effects of atrial natriuetic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) on human isolated resistance arteries and the mechanisms involved in vasorelaxation. Human subcutaneous resistance arteries were mounted in an isometric myograph and contracted with phenylephrine. CNP, but not ANP or BNP, relaxed arteries in a concentration dependent manner. The action of CNP was unaffected by removal of the endothelium, inhibition of nitric oxide synthase by NG-monomethyl-Larginine or inhibition of soluble guanylate cyclase by 1H-[1,2,4] oxadiazolo [4,3-alpha] quinoxalin-1-one. Blockade of cyclic GMPdependent kinase by 8- bromoguanosine- 3, 5- cyclic monophosphorothioate, Rp-isomer (Rp-8-Br-cGMPS) inhibited CNP relaxation. CNP relaxation was also inhibited by high potassium or iberiotoxin, indicating that it was due to opening of BKCa channels. Omapatrilat, a vasopeptidase inhibitor of neutral endopeptidase and angiotensin-converting enzyme, enhanced the effect of CNP and inhibited responses to Ang I. In summary, CNP, but not ANP or BNP, relaxes human resistance arteries by activating cyclic GMP-dependent kinase and BKCa. The effects of CNP are enhanced by vasopeptidase inhibition and this may contribute to the vasodilator effects of these agents in vivo. Since CNP is widely present in endothelium it may play a role in the regulation of peripheral resistance in man in physiological and pathological circumstances.

C-type natriuretic peptide in vascular physiology and disease

Natriuretic peptides play a critical role in coordination of fluid/electrolyte balance and vascular tone. The renal effects of circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are distinct from the paracrine effects of vascular C-type natriuretic peptide (CNP). CNP is widely expressed throughout the vasculature and is found in particularly high concentrations in the endothelium. Recent studies demonstrate that CNP is a novel endothelium-derived hyperpolarising factor (EDHF) that complements the actions of other endothelial vasorelaxant mediators such as nitric oxide (NO) and prostacyclin. Since several cardiovascular disorders are associated with dysfunction of natriuretic peptide activity, selective modulation of the natriuretic peptide pathways represents an important therapeutic target; whilst this has been exploited to some degree in terms of ANP/BNP, the therapeutic potential of CNP has yet to be tapped. This review focuses on recent findings on the actions and mechanism of locally produced endothelial-derived CNP in the cardiovascular system and highlights many potential avenues for therapeutic intervention, via modulation of CNP-signalling, in cardiovascular disease.

Role of natriuretic peptides in regulation of conduit artery distensibility

Arterial distensibility, assessed by the pulse-wave velocity (PWV), is an independent predictor of cardiovascular risk. We investigated whether natriuretic peptides, acting locally, modify conduit artery distensibility in vivo. All studies were conducted in anesthetized sheep ( n = 18) by using a validated ovine hindlimb model. In brief, the PWV was calculated, with the use of the foot-to-foot methodology, from two pressure waveforms recorded simultaneously with a high-fidelity dual pressure-sensing catheter placed in the common iliac artery. Drugs were infused either proximally, via the catheter to perfuse the segment of artery under study, or distally, via the sheath to control for any reflex changes in flow or sympathetic activation. First, the effects of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and c-type natriuretic peptide (CNP) were studied. Second, the role of endogenous ANP was investigated by infusing the natriuretic peptide receptor type A (NPRA)-selective receptor antagonist A71915. Third, A71915 was coinfused with ANP. Fourth, the NPRC-selective agonist cANF was infused. Infusion of CNP or des-[Gln18Ser19Gly20Leu21Gly22]-ANF-(4-23)-NH2 (cANF) had no effect on iliac PWV. However, infusion of ANP, and to a lesser degree BNP, resulted in a reduction in PWV (−9%; P < 0.01 and −6%; P < 0.05, respectively). A71915 increased iliac PWV from 2.97 ± 0.13 to 3.06 ± 0.13 m/s; P < 0.01. Coinfusion of A71915 with ANP completely abolished the effects of ANP ( P < 0.01). Importantly, ANP-BNP infusion via the sheath did not alter PWV. In conclusion, ANP, and to a lesser extent BNP, modify large artery distensibility via the NPRA receptor. Neither CNP nor cANF altered PWV, suggesting that the NPRB and NPRC receptors do not acutely influence distensibility in vivo.

[Atrial natriuretic factor: retrospective and perspectives]

Since the hypotensive and natriuretic properties of crude cardiac extracts were first demonstrated in 1981 in the rat, the effector molecule has been isolated, purified and synthesized. The hormonal factor is produced by atrial myocytes in mammals and stored as a prohormone. Secretion mainly results from a volemic stress inducing an atrial stretch. Secretion includes a maturation step. A peptide of 28 amino-acids (ANP) is then released into the bloodstream. ANP has a half-life of a few minutes. ANP binds to specific receptors expressed at the target cell surface. B-receptors mediate the biological actions of ANP by an increase in cGMP while C-receptors are involved in clearance of the peptide. The kidney as well as the cardiovascular and endocrine systems are the main target sites for ANP. The renal effects of ANP are expressed by an enhanced diuresis and natriuresis which may result from an increased glomerular filtration rate and/or a reduced tubular reabsorption of salt and water. Renal hemodynamics may also be modified due to a renal specific vasodilator effect of ANP. The reduction of systemic blood pressure may result from changes in cardiac output and/or in peripheral vascular resistance. Several neurohumoral interactions of ANP also contribute to sustain the cardiovascular and renal effects described above. In view of these properties, ANP is of particular interest in order to understand the homeostasis of salt and water under physiological as well as or physiopathological conditions. In this regard, therapeutic prospects are intensively investigated. Finally, evolutionary perspectives are actually considered from studies in lower vertebrates.

C-type natriuretic peptides are potent dilators of shark vascular smooth muscle

Previous studies of the effects of C-type natriuretic peptides (CNP) in intact mammals have demonstrated limited hypotensive responses, in contrast to other natriuretic peptides. Our previous studies, on isolated vascular smooth muscle (VSM) from various fish species, utilizing either mammalian or non-homologous fish atrial natriuretic peptides (ANP), have demonstrated vasodilation with a relatively high sensitivity (EC50 approximately 5 nM). The recent sequencing of a C-type natriuretic peptide from the heart of the dogfish shark, Squalus acanthias, has enabled us to compare the efficacy of this peptide on aortic VSM from that species with two other CNPs (from killifish and pig), as well as rat ANP. The EC50 of dilation for sCNP, as well as kCNP and pCNP, was 0.5 nM, over 15 times lower than the EC50 of the response to rANP. These data suggest that CNP is released from the dogfish shark heart and is a circulating hormone with potent vasodilatory effects, in sharp contrast to the apparent role of CNP predominantly as a brain neuropeptide in mammals.

Atrial natriuretic factor reduces renin release by opposing alpha-adrenoceptor activity

To examine how atrial natriuretic factor (ANF) inhibits renin release during renal sympathetic nerve stimulation, experiments were performed in barbiturate-anesthetized dogs. In five dogs, intravenous ANF infusion (50 ng.min-1.kg body wt-1) reduced renin release induced by renal nerve stimulation (1 Hz) from 16.8 +/- 8.4 to 3.5 +/- 2.1 micrograms angiotensin I (ANG I)/min. In two groups, renin release was raised by ureteral occlusion, which enhances the effects of beta-adrenoceptor stimulation and increased prostaglandin synthesis. During ureteral occlusion, intrarenal infusion of isoproterenol (0.2 micrograms.min-1.kg body wt-1) increased renin release in eight dogs to 82.6 +/- 10.9 micrograms ANG I/min, which was not significantly reduced by ANF infusion (81.1 +/- 10.1 micrograms ANG I/min). Similarly, intrarenal infusion of arachidonic acid (80 micrograms.min-1.kg body wt-1) during ureteral occlusion increased renin release in five dogs to 22.2 +/- 3.0 micrograms ANG I/min, which was not significantly reduced by ANF infusion (22.5 +/- 3.5 micrograms ANG I/min). Finally, in six dogs examined at free urine flow, intrarenal infusion of phenylephrine, an alpha-adrenergic agonist, raised renin release from 0.5 +/- 0.3 to 20.1 +/- 6.8 micrograms ANG I/min, which was reduced to 10.6 +/- 3.9 micrograms ANG I/min by intravenous ANF infusion (100 ng.min-1.kg body wt-1). These results indicate that ANF does not counteract stimulation of renin release by beta-adrenoceptors and prostaglandins but reduces nerve-stimulated renin release by opposing alpha-adrenoceptor activity.