Response of large and small vessels to alpha and beta adrenoceptor stimulation in heart failure: effect of angiotensin converting enzyme inhibition

Vena cava presents endothelial dysfunction prior to thoracic aorta in heart failure: the pivotal role of nNOS uncoupling/oxidative stress

Arterial endothelial dysfunction has been extensively studied in heart failure (HF). However, little is known about the adjustments shown by the venous system in this condition. Considering that inferior vena cava (VC) tone could influence cardiac performance and HF prognosis, the aim of the present study was to assess the VC and thoracic aorta (TA) endothelial function of HF-post-myocardial infarction (MI) rats, comparing both endothelial responses and signaling pathways developed. Vascular reactivity of TA and VC from HF post-MI and sham operated (SO) rats was assessed with a wire myograph, 4 weeks after coronary artery occlusion surgery. Nitric oxide (NO), H2O2 production and oxidative stress were evaluated in situ with fluorescent probes, while protein expression and dimer/monomer ratio was assessed by Western blot. VC from HF rats presented endothelial dysfunction, while TA exhibited higher acetylcholine (ACh)-induced vasodilation when compared with vessels from SO rats. TA exhibited increased ACh-induced NO production due to a higher coupling of endothelial and neuronal NO synthases isoforms (eNOS, nNOS), and enhanced expression of antioxidant enzymes. These adjustments, however, were absent in VC of HF post-MI rats, which exhibited uncoupled nNOS, oxidative stress and higher H2O2 bioavailability. Altogether, the present study suggests a differential regulation of endothelial function between VC and TA of HF post-MI rats, most likely due to nNOS uncoupling and compromised antioxidant defense.

Cardiac and Vascular α1-Adrenoceptors in Congestive Heart Failure: A Systematic Review

As heart failure (HF) is a devastating health problem worldwide, a better understanding and the development of more effective therapeutic approaches are required. HF is characterized by sympathetic system activation which stimulates α- and β-adrenoceptors (ARs). The exposure of the cardiovascular system to the increased locally released and circulating levels of catecholamines leads to a well-described downregulation and desensitization of β-ARs. However, information on the role of α-AR is limited. We have performed a systematic literature review examining the role of both cardiac and vascular α1-ARs in HF using 5 databases for our search. All three α1-AR subtypes (α1A, α1B and α1D) are expressed in human and animal hearts and blood vessels in a tissue-dependent manner. We summarize the changes observed in HF regarding the density, signaling and responses of α1-ARs. Conflicting findings arise from different studies concerning the influence that HF has on α1-AR expression and function; in contrast to β-ARs there is no consistent evidence for down-regulation or desensitization of cardiac or vascular α1-ARs. Whether α1-ARs are a therapeutic target in HF remains a matter of debate.

Effects of Apelin on Left Ventricular-Arterial Coupling and Mechanical Efficiency in Rats with Ischemic Heart Failure

Apelin plays important roles in cardiovascular homeostasis. However, its effects on the mechanoenergetics of heart failure (HF) are unavailable. We attempted to investigate the effects of apelin on the left ventricular-arterial coupling (VAC) and mechanical efficiency in rats with HF. HF was induced in rats by the ligation of the left coronary artery. The ischemic HF rats were treated with apelin or saline for 12 weeks. The sham-operated animals served as the control. The left ventricular (LV) afterload and the systolic and diastolic functions, as well as the mechanoenergetic indices were estimated from the pressure-volume loops. Myocardial fibrosis by Masson's trichrome staining, myocardial apoptosis by TUNEL, and collagen content in the aorta as well as media area in the aorta and the mesenteric arteries were determined. Our data indicated that HF rats manifested an increased arterial load (Ea), a declined systolic function (reduced ejection fraction, +dP/dt_max, end-systolic elastance, and stroke work), an abnormal diastolic function (elevated end-diastolic pressure, τ, and declined −dP/dt_max), and decreased mechanical efficiency. Apelin treatment improved those indices. Concomitantly, increased fibrosis in the LV myocardium and the aorta and enhanced apoptosis in the LV were partially restored by apelin treatment. A declined wall-to-lumen ratio in the mesenteric arteries of the untreated HF rats was further reduced in the apelin-treated group. We concluded that the rats with ischemic HF were characterized by deteriorated LV mechanoenergetics. Apelin improved mechanical efficiency, at least in part, due to the inhibiting cardiac fibrosis and apoptosis in the LV myocardium, reducing collagen deposition in the aorta and dilating the resistant artery.

Impaired neuronal and vascular responses to angiotensin II in a rabbit congestive heart failure model

Congestive heart failure (CHF) is characterised by activation of the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (SNS). Both systems are known to interact and to potentiate each other's activities. We recently demonstrated that angiotensin II (Ang II) enhances sympathetic nerve traffic via prejunctionally-located AT1-receptors. At present, little is known about the effects of Ang II at the level of the sympathetic neurones in CHF.

Accordingly, we investigated the effect of Ang II in the presence and absence of the AT1-receptor antagonist, eprosartan, on stimulation-induced nerve traffic in isolated thoracic aorta preparations obtained from rabbits suffering from experimentally-induced CHF. Control-preparations were obtained from age-matched animals. Sympathetic activity was assessed by a [3H]noradrenaline spill-over model. Additionally, Ang II constrictor responses were compared between CHF and control vessels in the presence and absence of eprosartan. Additionally, to study postjunctional facilitation, the effects of Ang II on postsynaptic α-adrenoceptor-mediated responses were studied using noradrenaline.

Stimulation-evoked SNS-neurotransmission was similar in both groups (CHF versus control). Ang II (0.1 nM—0.1 µM) caused a concentration-dependent increase of the stimulation-evoked sympathetic outflow in both groups, with a maximum at 10 nM (control [n=7], FR2/FR12.03±0.11 and CHF-preparations [n=7], FR2/FR11.71±0.07). The enhancement by Ang II was decreased in CHF-preparations compared with controls (p<0.05). Eprosartan concentration-dependently attenuated the Ang II-enhanced (10 nM) sympathetic outflow in both CHF- and control preparations. The sympathoinhibitory potency of eprosartan was similar in both groups (control pIC508.81±0.31; CHF 8.65±0.42).

Ang II (1 nM—0.3 µM) concentration-dependently increased the contractile force in control preparations (Emax21.64±3.86 mN, pD27.63±0.02, n=7). Eprosartan (1 nM—0.1 µM) influenced the Ang IIcontractions via a mixed form of antagonism. In CHF-preparations, Ang II caused impaired vascular contraction. The KCl-induced contraction was decreased in the CHF- compared with control preparations (13.02±0.64 mN versus 30.40±0.89 mN). The relative Ang II contraction (% of KCl) was also decreased (2.3% vs. 58.0%). Concentration-response curves to noradrenaline (%KCl) were similar (control pD26.93±0.05, Emax131.0±2.7; CHF pD27.00±0.05, Emax136.7±2.6) (p>0.05) and were not affected by Ang II.

We conclude that Ang II-enhanced sympathetic neurotransmission is mediated by the prejunctional AT1-receptor in both control and CHF-preparations. The decreased facilitation of SNS effects by Ang II may be explained by down-regulation or desensitisation of the neuronal AT1-receptor. Additionally, the aortic contractile capacity in heart failure rabbits appears to be decreased, probably as a result of heart failure-associated neuroendocrine and functional changes.

Noradrenaline-induced increases in calcium and tension in skeletal muscle conductance and resistance arteries from rats with post-infarction heart failure

We tested the hypothesis that arterial reactivity to noradrenaline is augmented in congestive heart failure (CHF), which could contribute to the deleterious changes in peripheral vascular resistance and compliance in this condition. From male Wistar rats with post-infarction CHF and sham-operated rats, skeletal muscle conductance and resistance arteries (mean lumen diameters: 514 and 186 microm) were isolated and mounted on wire myographs, and wall tension was recorded in response to cumulative application of acetylcholine and noradrenaline to the vessel segments. In a subset of experiments, wall tension and cytosolic free calcium ion concentration [Ca(2+)](i) were recorded simultaneously during noradrenaline application, using wire myography and the FURA-2 technique. No significant differences were found in the arterial baseline levels of [Ca(2+)](i) or tension between CHF and sham rats. In the resistance arteries of CHF rats, the noradrenaline-induced increases in [Ca(2+)](i) were significantly enhanced (P=0.003). Despite the augmented [Ca(2+)](i) levels, the tension responses to noradrenaline were unaltered in these arteries. In the conductance arteries, there were no significant differences in noradrenaline-induced [Ca(2+)](i) or tension responses between CHF and control rats. CHF did not alter vascular morphology or change vascular relaxations to acetylcholine in either type of artery. In conclusion, these results do not support the contention that arterial reactivity to noradrenaline is augmented in the skeletal muscle vascular bed in CHF. On the contrary, the unchanged contractile responsiveness in the resistance arteries despite the enhanced levels of [Ca(2+)](i) during noradrenaline application suggests that the contractile function of these vessels is compromised in CHF. Neither vascular remodeling, endothelial dysfunction nor changes in baseline vascular tone could be demonstrated in the skeletal muscle vascular bed of this animal model of heart failure.

Mechanism of increased alpha-adrenoceptor-mediated contraction in small resistance arteries of rats with heart failure

1. Alterations in a(1)-adrenoceptor signalling that result in enhanced contraction in resistance arteries in heart failure are not well characterized. To clarify whether this enhanced constriction is due to Ca(2+)-dependent or -independent effects, we measured the phenylephrine-induced changes in [Ca(2+)](i) in the presence of a Rho kinase inhibitor or an inositol 1,4,5-trisphosphate (IP(3)) receptor inhibitor. 2. Heart failure was induced in rats by ligation of the left coronary artery. Changes in the internal diameter of pressurized small femoral arteries were examined using videomicroscopy. Phenylephrine concentration-response curves, constructed in the presence of the Rho kinase inhibitor Y27632 (0.3 micromol/L) or the IP(3) receptor inhibitor xestospongin C (0.3 micromol/L), were compared in heart failure rats and sham-operated (control) rats; fura-2 Ca(2+) signals were measured in the arteries of both groups. 3. The heart : bodyweight ratio, lung : bodyweight ratio, left ventricular end-diastolic pressure and plasma B-type natriuretic peptide were significantly higher in heart failure rats compared with control rats. Phenylephrine-induced contractile responses and increases in [Ca(2+)](i) were significantly greater in arteries from heart failure rats compared with arteries from control rats. At 0.3 micromol/L, Y27632 selectively inhibited phenylephrine-induced constrictions of heart failure arteries, but had no effect on the increase in [Ca(2+)](i). 4. Immunohistochemical staining for Rho kinase was greater in heart failure rats compared with control rats. 5. The degree of inhibition of both the phenylephrine-induced constriction and the increase in [Ca(2+)](i) by xestospongin C (0.3 micromol/L) was greater in arteries from heart failure rats than in those from control rats. 6. The increased contractile response to phenylephrine in arteries of heart failure rats results from IP(3)-dependent increases in [Ca(2+)](i) and from an enhanced Ca(2+) sensitivity via a Rho kinase-dependent mechanism.

Ca2+ sensitisation of force production by noradrenaline in femoral conductance and resistance arteries from rats with postinfarction congestive heart failure

In this study we tested the hypothesis that arterial myofilament Ca(2+) sensitivity and/or the Ca(2+) sensitising effect of noradrenaline (NA) is enhanced in post-infarction congestive heart failure (CHF), which could contribute to the high peripheral vascular resistance in this condition. Femoral skeletal muscle resistance and conductance arteries (mean lumen diameters of 159 and 519 microm) from rats with CHF and sham-operated control rats were used. Isometric tension development and intracellular free calcium concentration ([Ca(2+)](i)) were measured simultaneously in isolated vessel segments using wire myography and the FURA-2 fluorescence technique. In conductance and resistance arteries, the resting levels of [Ca(2+)](i) and tension in physiological saline solution (PSS) and active tension in response to single doses of 125 mM K(+) (KPSS) were unaffected by CHF. During cumulative application of extracellular Ca(2+) to arteries depolarised with 125 mM K(+) or activated with 30 microM NA, [Ca(2+)](i) and vessel wall tension were similar in CHF and control rats. However, the conductance arteries showed significantly higher calcium sensitivity than resistance arteries in these experiments. We conclude that an abnormality in the sensitivity of the contractile apparatus to Ca(2+), or in NA-induced Ca(2+) sensitisation in arterial vascular smooth muscle cells is unlikely to contribute to the ubiquitously elevated vascular resistance associated with CHF. However, our data demonstrate significant differences in vascular Ca(2+) handling, myofilament Ca(2+) sensitivity and tension development between resistance and conductance arteries, regardless of CHF.

Decreased facilitation by angiotensin II of noradrenergic neurotransmission in isolated mesenteric artery of rabbits with chronic heart failure

Both in human and in experimental heart failure (HF), the renin-angiotensin system and the sympathetic nervous system are activated. In a previous study a facilitatory action of angiotensin II (Ang II) was shown in the rabbit mesenteric artery, which was mediated via prejunctionally located Ang II type 1 (AT ) receptors. Very little is known about the effects of Ang II on sympathetic neurotransmission at the peripheral level in congestive heart failure (CFH). Accordingly, in the isolated mesenteric arteries obtained from rabbits with experimentally induced CHF, as well as in age-matched control rabbits, the effect of Ang II on contractions provoked by electrical field stimulation was investigated in the presence and absence of the AT receptor antagonist eprosartan. Additionally, to investigate a possible postjunctional facilitation, the effects of Ang II on alpha-adrenoceptor-mediated responses were studied using noradrenaline (NA). Lastly, the vasoconstrictor effects of Ang II were compared between HF rabbits and controls, by constructing concentration-response curves to Ang II. In control rabbits, Ang II 0.5 n caused an enhancement of stimulation-induced responses by a factor 3.2 +/- 0.5, 2.4 +/- 0.3, and 1.5 +/- 0.08, at 1, 2, and 4 Hz, respectively ( < 0.05 at all frequencies compared with vehicle). In rabbits with HF, the enhancement by Ang II (0.5 n ) amounted to a factor 2.1 +/- 0.2, 1.7 +/- 0.1, and 1.2 +/- 0.04, at 1, 2, and 4 Hz, respectively ( < 0.05 compared with vehicle at all frequencies). Accordingly, the enhancing effect of Ang II was more pronounced in the control group compared with rabbits with HF ( < 0.05 at each frequency). Eprosartan (1 nM -0.1 microM) could inhibit the facilitatory effects of Ang II in arteries from HF as well as from control rabbits. Contractile responses to exogenous NA (3 n -0.1 m ) were the same in HF rabbits and controls, and they were unaltered in the presence of Ang II 0.5 n Ang II (0.1 nM -1 microM) caused a concentration-dependent increase in contractile force, which was the same in HF rabbits and controls. From these findings it can be concluded that in rabbits with CHF as well as in control animals, Ang II facilitates the stimulation-induced vasoconstrictor responses via prejunctionally located AT receptors. The facilitating effect was decreased in vessels obtained from rabbits with CHF, whereas responses to exogenous Ang II were unchanged. These findings may be explained by downregulation or uncoupling of the prejunctional AT receptor.

Exaggerated cardiovascular effects of cocaine in conscious dogs with pacing-induced dilated cardiomyopathy

BACKGROUND

The aim of this study was to explore the characteristics and mechanisms of the cardiovascular effects of cocaine in dilated cardiomyopathy.

METHODS AND RESULTS

We studied the cardiovascular responses to acute intravenous cocaine (1 mg/kg) in 8 conscious, chronically instrumented dogs before and after the development of dilated cardiomyopathy induced by rapid ventricular pacing. To help elucidate the role of altered baroreflex function in mediating the cardiovascular effects of cocaine, we also studied responses in 3 conscious, chronically instrumented dogs that had undergone surgical sinoaortic baroreceptor denervation. Cocaine produced greater increases in heart rate (+57 +/- 8% from 112 +/- 5 beats/min versus +28 +/- 3% from 100 +/- 4 beats/min; P <.01), first derivative of left ventricular pressure (+30 +/- 5% from 1,714 +/- 147 mm Hg/sec versus +15 +/- 3% from 3,032 +/- 199 mm Hg/sec; P <.01), coronary vascular resistance (+28 +/- 5% from 2.3 +/- 0.3 mm Hg/mL/min versus +11 +/- 5% from 2.2 +/- 0.3 mm Hg/mL/min; P <.05) and plasma norepinephrine concentration (+130 +/- 31% from 462 +/- 102 pg/mL versus +86 +/- 32% from 286 +/- 77 pg/mL; P <.05) in dogs with dilated cardiomyopathy as compared to controls. In addition, responses were much more rapid in onset following the development of dilated cardiomyopathy. Chronotropic and inotropic responses to cocaine were similarly rapid and exaggerated in dogs after baroreceptor denervation.

CONCLUSIONS

Cocaine produces rapid and exaggerated chronotropic, inotropic, and coronary vasoconstrictor responses in conscious dogs with pacing-induced dilated cardiomyopathy. Alterations in arterial baroreflex function may play a role in these observations, which in turn may underlie the clinically observed association between cocaine and heart failure.

Effects of angiotensin II AT1-receptor blockade on coronary dynamics, function, and structure in postischemic heart failure in rats

Angiotensin II AT1-receptor blockers (AT1-s) prolong survival in experimental postischemic (coronary artery ligation) heart failure (CHF) in rats. The goal of this study was to investigate whether potential beneficial effects of short- and/or long-term treatment with AT1-s on coronary dynamics, function, and structure develop along with the drug-induced survival prolongation in this model. Coronary blood flow was measured (fluorescent microspheres) in conscious sham, untreated, and irbesartan-treated (50 mg/kg daily for 6 weeks or 6 months, starting 8 days after surgery) CHF rats at baseline and at maximal vasodilatation induced by dipyridamole, and coronary dilatation reserve (CDR) was calculated as the ratio of maximal to baseline coronary flow. Coronary endothelial function was assessed in vitro by measuring the coronary relaxant responses to acetylcholine in the three groups of animals. Finally, cardiac hypertrophy and pericoronary fibrosis also were investigated. In CHF rats, left (LV) and right (RV) ventricular CDR were markedly depressed at both 7 weeks and 6 months after ligation, whereas coronary endothelial function was significantly impaired only after 6 months. Short-term AT1-receptor blockade with irbesartan did not prevent CDR deterioration at 7 weeks, nor did it significantly oppose cardiac hypertrophy and pericoronary fibrosis development. Prolonged AT1-receptor blockade prevented both RV CDR deterioration and coronary endothelial function impairment. It also limited significantly the increase in LV end diastolic pressure and the development of cardiac hypertrophy and pericoronary fibrosis. In conclusion, in postischemic CHF in rats, alterations of CDR precede those of coronary endothelial function. Long-, but not short-term AT1-receptor blockade prevents endothelial function degradation, opposes RV CDR impairment, prevents pericoronary fibrosis development, and improves systemic hemodynamics. These effects of AT1-s on coronary dynamics, function, and structure (i.e., on myocardial perfusion) may contribute to the drug-induced survival prolongation in this model.

Cardiac positron emission tomography imaging with [11C]hydroxyephedrine, a specific tracer for sympathetic nerve endings, and its functional correlates in congestive heart failure

The integrative mechanisms of autonomic dysfunction in congestive heart failure (CHF) remain poorly understood. We sought to study cardiac retention of [11C]hydroxyephedrine (HED), a specific tracer for sympathetic presynaptic innervation, and its functional correlates in CHF. Thirty patients with mild to moderate heart failure underwent resting cardiac HED positron emission tomography imaging, spectrum analysis testing of systolic pressure and heart rate variability in the resting supine and 70 degrees head-up tilt positions, and testing of baroreflex sensitivity. Compared with control subjects, global myocardial HED retention index was reduced by 30% (p <0.01) in patients with CHF. The HED retention index did not correlate significantly with heart rate variability. However, it correlated with baroreflex sensitivity at rest (r = 0.43, p = 0.05) and with systolic pressure low-frequency (0.03 to 0.15 Hz) variability at head-up tilt (r = 0.76, p <0.01), as well as with low-frequency systolic pressure variability response from baseline to tilt (r = 0.75, p <0.01). We conclude that cardiac HED retention is reduced in patients with CHF. This correlates with blunted vascular sympathetic effector responses during posture-induced reflex activation and baroreflex control of heart rate, suggesting an interdependence between cardiac presynaptic innervation abnormalities and neural mechanisms important to blood pressure maintenance in CHF.

Effect of short- and long-term heart failure on small artery morphology and endothelial function in the rat

Chronic heart failure (HF) is associated with hemodynamic changes and activation of several neurohormonal systems, which are able both to inhibit and to facilitate arterial growth or remodeling and also to influence endothelial function. As these vascular changes may depend on the duration of HF, we evaluated morphologic and endothelial functional alterations in a rat model of HF after a short and long duration of HF. Rats with coronary ligation and sham-operated controls were investigated either 8 or 26 weeks after the operation with measurements of hemodynamics and isolated mesenteric small artery morphology and endothelial function. The effect of HF and duration of HF were examined by using two-way analysis of variance (ANOVA). HF rats had altered hemodynamics with reductions in cardiac output, left ventricular systolic pressure, and mean blood pressure, whereas left ventricular diastolic pressure was increased. HF caused remodeling of anatomically well-defined mesenteric small arteries with a reduction in media thickness and media-to-lumen ratio, but without change in the media cross-sectional area. Neither HF nor time had any influence on sensitivity or maximal relaxation to acetylcholine in the presence of indomethacin, but HF reduced vasoconstriction due to nitric oxide synthase blockade with N(G)-nitro-L-arginine independent of time. Our results indicate that HF, induced by coronary ligation in the rat, has a remodeling effect on mesenteric small arteries. However, the remodeling is moderate compared with that observed in hypertension. Furthermore, our results suggest that HF reduces basal release of NO.