Effects of dopamine beta-hydroxylase inhibition with nepicastat on the progression of left ventricular dysfunction and remodeling in dogs with chronic heart failure

Management of Chronic Congestive Heart Failure Caused by Myxomatous Mitral Valve Disease in Dogs: A Narrative Review from 1970 to 2020

Simple Summary

Myxomatous mitral valve disease (MMVD) is the most common acquired cardiovascular disease in dogs. The progression of the disease and the increasing severity of valvular regurgitation cause a volume overload of the left heart, leading to left atrial and ventricular remodeling and congestive heart failure (CHF). The treatment of chronic CHF secondary to MMVD in dogs has not always been the same over time. In the last fifty years, the drugs utilized have considerably changed, as well as the therapeutic protocols. Some drugs have also changed their intended use. An analysis of the literature concerning the therapy of chronic heart failure in dogs affected by this widespread degenerative disease is not available; a synthesis of the published literature on this topic and a description of its current state of art are needed. To the authors’ knowledge, a review of this topic has never been published in veterinary medicine; therefore, the aim of this study is to overview the treatments of chronic CHF secondary to MMVD in dogs from 1970 to 2020 using the general framework of narrative reviews.

Abstract

The treatment of chronic congestive heart failure (CHF), secondary to myxomatous mitral valve disease (MMVD) in dogs, has considerably changed in the last fifty years. An analysis of the literature concerning the therapy of chronic CHF in dogs affected by MMVD is not available, and it is needed. Narrative reviews (NRs) are aimed at identifying and summarizing what has been previously published, avoiding duplications, and seeking new study areas that have not yet been addressed. The most accessible open-access databases, PubMed, Embase, and Google Scholar, were chosen, and the searching time frame was set in five decades, from 1970 to 2020. The 384 selected studies were classified into categories depending on the aim of the study, the population target, the pathogenesis of MMVD (natural/induced), and the resulting CHF. Over the years, the types of studies have increased considerably in veterinary medicine. In particular, there have been 43 (24.29%) clinical trials, 41 (23.16%) randomized controlled trials, 10 (5.65%) cross-over trials, 40 (22.60%) reviews, 5 (2.82%) comparative studies, 17 (9.60%) case-control studies, 2 (1.13%) cohort studies, 2 (1.13%) experimental studies, 2 (1.13%) questionnaires, 6 (3.40%) case-reports, 7 (3.95%) retrospective studies, and 2 (1.13%) guidelines. The experimental studies on dogs with an induced form of the disease were less numerous (49–27.68%) than the studies on dogs affected by spontaneous MMVD (128–72.32%). The therapy of chronic CHF in dogs has considerably changed in the last fifty years: in the last century, some of the currently prescribed drugs did not exist yet, while others had different indications.

Treatment With Nepicastat Decreases Contextual Traumatic Memories Persistence in Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a common anxiety mental disorder and can be manifested after exposure to a real or perceived life-threatening event. Increased noradrenaline and adrenaline in plasma and urine have been documented in PTSD. Dopamine-β-hydroxylase (DBH) catalyzes the conversion of dopamine to noradrenaline and consequently, DBH inhibition reduces catecholamines. Our aim was to evaluate if nepicastat treatment decreases PTSD signs in an animal model. Wild-type (129x1/SvJ) female mice were submitted to PTSD induction protocol. DBH-inhibitor nepicastat (30 mg/kg) or vehicle (0.2% HPMC) were administered once daily since day 0 until day 7 or 12. The percentage of freezing was calculated on days 0, 1, 2, and 7, and behavioral tests were performed. Quantification of nepicastat in plasma and DBH activity in the adrenal gland was evaluated. Catecholamines were quantified by HPLC with electrochemical detection. mRNA expression of Npas4 and Bdnf in hippocampus was evaluated by qPCR.Mice in the PTSD-group and treated with nepicastat showed a decrease in freezing, and an increase in the time spent and entries in open arms in elevated plus maze test. In mice treated with nepicastat, adrenal gland DBH activity was decreased, and catecholamines were also decreased in plasma and tissues. On day 7, in mice treated with nepicastat, there was an increase of Npas4 and Bdnf mRNA expression in the hippocampus.In conclusion, DBH inhibitor nepicastat has an effect consistent with a decrease in the persistence of traumatic memories and anxiety-like behavior in this PTSD mice model. The disruption of traumatic memories through interference with the formation, consolidation, retrieval, and/or expression processes may be important to decrease PTSD symptoms and signs. The increase in Npas4 and Bdnf mRNA expression in the hippocampus may be important to develop a weaker traumatic contextual memory after nepicastat treatment.

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.

Effects of Angiotensin-Neprilysin Inhibition in Canines with Experimentally Induced Cardiorenal Syndrome

BACKGROUND

Sacubitril/valsartan (Sac/Val), a combined angiotensin-II receptor blocker (Val) and neprilysin inhibitor (Sac) in a 1:1 molar ratio, was shown to decrease the risk of cardiovascular death or heart failure (HF) hospitalization in patients with HF and reduced left ventricular (LV) ejection fraction. This study examined the effects of Sac/Val on LV structure, function, and bioenergetics, and on biomarkers of kidney injury and kidney function in dogs with experimental cardiorenal syndrome.

METHODS AND RESULTS

Fourteen dogs with cardiorenal syndrome (coronary microembolization-induced HF and renal dysfunction) were randomized to 3 months Sac/Val therapy (100 mg once daily, n = 7) or no therapy (control, n = 7). LV ejection fraction and troponin-I, as well as biomarkers of kidney injury/function including serum creatinine and urinary kidney injury molecule-1 were measured before and at end of therapy and the change (treatment effect change) calculated. Mitochondrial function measures, including the maximum rate of adenosine triphosphate synthesis, were measured in isolated cardiomyocytes at end of therapy. In Sac/Val dogs, the change in ejection fraction increased compared with controls, 6.9 ± 1.4 vs 0.7 ± 0.6%, P < .002, whereas change in troponin I decreased, -0.16 ± 0.03 vs -0.03 ± 0.02 ng/mL, P < .001. Urinary change in kidney injury molecule 1 decreased in Sac/Val-treated dogs compared with controls, -17.2 ± 7.9 vs 7.7 ± 3.0 mg/mL, P < .007, whereas the change in serum creatinine was not significantly different. Treatment with Sac/Val increased adenosine triphosphate synthesis compared with controls, 3240 ± 121 vs 986 ± 84 RLU/µg protein, P < .05.

CONCLUSIONS

In dogs with cardiorenal syndrome, Sac/Val improves LV systolic function, improves mitochondrial function and decreases biomarkers of heart and kidney injury. The results offer mechanistic insights into the benefits of Sac/Val in HF with compromised renal function.

Impaired Baroreflex Function in an Ovine Model of Chronic Heart Failure Induced by Multiple Coronary Microembolizations

Testing new therapies in heart failure (HF) requires a chronic stable model of HF in large animals. Microembolization of the coronary arteries has been used to model HF previously; however, neural control has not been previously explored in this model. Thus the aim of this study was to further characterize neural control in this model of HF. HF was induced by infusion of microspheres (45 micron; 1.3 ml) into the proximal left coronary artery or left descending coronary arteries, with three sequential embolizations over 3 weeks. Twelve to 14 weeks after the final embolization, and when ejection fraction had decreased below 45%, animals were instrumented to record blood pressure and heart rate. Baroreflex control of heart rate was investigated in conscious animals. Additionally, pressure-volume loops were constructed under anesthesia. Embolization-induced HF was associated with a decrease in mean arterial pressure (67 ± 2 vs. 85 ± 4 mmHg, p < 0.05), an increase in heart rate (108 ± 4 vs. 94 ± 4 bpm, p < 0.05), and a significant increase in left ventricular end-diastolic pressure (11.4 ± 2 vs. 6.2 ± 1 mmHg, p < 0.01). Under conscious conditions, there was a significant decrease in the gain (-8.2 ± 2 vs. -4.1 ± 1 beats/min/mmHg, p < 0.05) as well as the lower plateau of the baroreflex in HF compared to control animals. HF was also associated with significantly increased respiratory rate (107 ± 4 vs. 87 ± 4 breaths/min, p < 0.01) and incidence of apneas (520 ± 24 vs. 191 ± 8 apnea periods >4 s, p < 0.05), compared to control sheep. The microembolization model of heart failure is associated with an increase in left ventricular end-diastolic pressure, impaired cardiac function, and altered baroreflex control of the heart. These findings suggest this chronic model of HF is appropriate to use for investigating interventions aimed at improving neural control in HF.

Silent disease progression in clinically stable heart failure

Heart failure with reduced ejection fraction (HFrEF) is a progressive disorder whereby cardiac structure and function continue to deteriorate, often despite the absence of clinically apparent signs and symptoms of a worsening disease state. This silent yet progressive nature of HFrEF can contribute to the increased risk of death-even in patients who are 'clinically stable', or who are asymptomatic or only mildly symptomatic-because it often goes undetected and/or undertreated. Current therapies are aimed at improving clinical symptoms, and several agents more directly target the underlying causes of disease; however, new therapies are needed that can more fully address factors responsible for underlying progressive cardiac dysfunction. In this review, mechanisms that drive HFrEF, including ongoing cardiomyocyte loss, mitochondrial abnormalities, impaired calcium cycling, elevated LV wall stress, reactive interstitial fibrosis, and cardiomyocyte hypertrophy, are discussed. Additionally, limitations of current HF therapies are reviewed, with a focus on how these therapies are designed to counteract the deleterious effects of compensatory neurohumoral activation but do not fully prevent disease progression. Finally, new investigational therapies that may improve the underlying molecular, cellular, and structural abnormalities associated with HF progression are reviewed.

Chronic Therapy With Elamipretide (MTP-131), a Novel Mitochondria-Targeting Peptide, Improves Left Ventricular and Mitochondrial Function in Dogs With Advanced Heart Failure

BACKGROUND

Elamipretide (MTP-131), a novel mitochondria-targeting peptide, was shown to reduce infarct size in animals with myocardial infarction and improve renal function in pigs with acute and chronic kidney injury. This study examined the effects of chronic therapy with elamipretide on left ventricular (LV) and mitochondrial function in dogs with heart failure (HF).

METHODS AND RESULTS

Fourteen dogs with microembolization-induced HF were randomized to 3 months monotherapy with subcutaneous injections of elamipretide (0.5 mg/kg once daily, HF+ELA, n=7) or saline (control, HF-CON, n=7). LV ejection fraction, plasma n-terminal pro-brain natriuretic peptide, tumor necrosis factor-α, and C-reactive protein were measured before (pretreatment) and 3 months after initiating therapy (post-treatment). Mitochondrial respiration, membrane potential (Δψm), maximum rate of ATP synthesis, and ATP/ADP ratio were measured in isolated LV cardiomyocytes obtained at post-treatment. In HF-CON dogs, ejection fraction decreased at post-treatment compared with pretreatment (29 ± 1% versus 31 ± 2%), whereas in HF+ELA dogs, ejection fraction significantly increased at post-treatment compared with pretreatment (36 ± 2% versus 30 ± 2%; P<0.05). In HF-CON, n-terminal pro-brain natriuretic peptide increased by 88 ± 120 pg/mL during follow-up but decreased significantly by 774 ± 85 pg/mL in HF+ELA dogs (P<0.001). Treatment with elamipretide also normalized plasma tumor necrosis factor-α and C-reactive protein and restored mitochondrial state-3 respiration, Δψm, rate of ATP synthesis, and ATP/ADP ratio (ATP/ADP: 0.38 ± 0.04 HF-CON versus 1.16 ± 0.15 HF+ELA; P<0.001).

CONCLUSIONS

Long-term therapy with elamipretide improves LV systolic function, normalizes plasma biomarkers, and reverses mitochondrial abnormalities in LV myocardium of dogs with advanced HF. The results support the development of elamipretide for the treatment of HF.

Heart failure: novel therapeutic approaches

Heart failure (HF) is a complex clinical syndrome that can result from any structural or functional cardiac disorders that impairs the ability of the ventricle to fill with or eject blood. Despite effective medical interventions, mortality and morbidity remain substantial. There have been significant advances in the therapy of HF in recent decades, such as the introduction of beta-blockers and antagonists of the renin-angiotensin system but still there is a major unmet need for better therapies for HF. In the present era, pathophysiology of HF has been explored. Various novel pathways, molecular sites have been identified, which contribute to the progression of the disease. By targeting these sites, newer pharmacological agents have been developed, which can play a promising role in the treatment of HF. This article focuses on recent advancements in pharmacotherapy of HF, which include agents targeting myocardial contractility, cytokines and inflammation, fibrosis and remodeling, myocardial metabolism, oxidative stress, and other newly defined pathways.

Structural remodeling of the heart and its premotor cardioinhibitory vagal neurons following T(5) spinal cord transection

Midthoracic spinal cord injury (SCI) is associated with enhanced cardiac sympathetic activity and reduced cardiac parasympathetic activity. The enhanced cardiac sympathetic activity is associated with sympathetic structural plasticity within the stellate ganglia, spinal cord segments T1-T4, and heart. However, changes to cardiac parasympathetic centers rostral to an experimental SCI are relatively unknown. Importantly, reduced vagal activity is a predictor of high mortality. Furthermore, this autonomic dysregulation promotes progressive left ventricular (LV) structural remodeling. Accordingly, we hypothesized that midthoracic spinal cord injury is associated with structural plasticity in premotor (preganglionic parasympathetic neurons) cardioinhibitory vagal neurons located within the nucleus ambiguus as well as LV structural remodeling. To test this hypothesis, dendritic arborization and morphology (cholera toxin B immunohistochemistry and Sholl analysis) of cardiac projecting premotor cardioinhibitory vagal neurons located within the nucleus ambiguus were determined in intact (sham transected) and thoracic level 5 transected (T5X) rats. In addition, LV chamber size, wall thickness, and collagen content (Masson trichrome stain and structural analysis) were determined. Midthoracic SCI was associated with structural changes within the nucleus ambiguus and heart. Specifically, following T5 spinal cord transection, there was a significant increase in cardiac parasympathetic preganglionic neuron dendritic arborization, soma area, maximum dendritic length, and number of intersections/animal. This parasympathetic structural remodeling was associated with a profound LV structural remodeling. Specifically, T5 spinal cord transection increased LV chamber area, reduced LV wall thickness, and increased collagen content. Accordingly, results document a dynamic interaction between the heart and its parasympathetic innervation.

Evaluation of docosahexaenoic acid in a dog model of hypertension induced left ventricular hypertrophy

Marine n-3 polyunsaturated fatty acids alter cardiac phospholipids and prevent cardiac pathology in rodents subjected to pressure overload. This approach has not been evaluated in humans or large animals with hypertension-induced pathological hypertrophy. We evaluated docosahexaenoic acid (DHA) in old female dogs with hypertension caused by 16 weeks of aldosterone infusion. Aldosterone-induced hypertension resulted in concentric left ventricular (LV) hypertrophy and impaired diastolic function in placebo-treated dogs. DHA supplementation increased DHA and depleted arachidonic acid in cardiac phospholipids, but did not improve LV parameters compared to placebo. Surprisingly, DHA significantly increased serum aldosterone concentration and blood pressure compared to placebo. Cardiac mitochondrial yield was decreased in placebo-treated hypertensive dogs compared to normal animals, which was prevented by DHA. Extensive analysis of mitochondrial function found no differences between DHA and placebo groups. In conclusion, DHA did not favorably impact mitochondrial or LV function in aldosterone hypertensive dogs.

Chronic therapy with a partial adenosine A1-receptor agonist improves left ventricular function and remodeling in dogs with advanced heart failure

BACKGROUND

Adenosine elicits cardioprotection through A1-receptor activation. Therapy with adenosine A1-receptor agonists, however, is limited by undesirable actions of full agonism, such as bradycardia. This study examined the effects of capadenoson (CAP), a partial adenosine A1-receptor agonist, on left ventricular (LV) function and remodeling in dogs with heart failure.

METHODS AND RESULTS

Twelve dogs with microembolization-induced heart failure were randomized to 12 weeks oral therapy with CAP (7.5 mg BID; n=6) or to no therapy (control; n=6). LV end-diastolic and end-systolic volumes, ejection fraction, plasma norepinephrine, and n-terminal pro-brain natriuretic peptide were measured before (pre) and 1 and 12 weeks after therapy (post). LV tissue obtained at post was used to assess volume fraction of interstitial fibrosis, sarcoplasmic reticulum calcium ATPase-2a activity, expression of mitochondria uncoupling proteins (UCP) and glucose transporters (GLUT). In controls, end-diastolic and end-systolic volumes increased and ejection fraction decreased significantly from pre to post (ejection fraction, 30±2 versus 27±1%; P<0.05). In CAP-treated dogs, end-diastolic volume was unchanged; ejection fraction increased significantly after 1 week (36±2 versus 27±2%; P<0.05) with a further increase at post (39±2%; P<0.05), whereas end-systolic volume decreased. CAP significantly decreased volume fraction of interstitial fibrosis, normalized sarcoplasmic reticulum calcium ATPase-2a activity and expression of UCP-2 and UCP-3, and GLUT-1 and GLUT-2 and significantly decreased plasma norepinephrine and n-terminal pro-brain natriuretic peptide.

CONCLUSIONS

In heart failure dogs, CAP improves LV function and prevents progressive remodeling. Improvement of LV systolic function occurs early after initiating therapy. The results support development of partial adenosine A1-receptor agonists for the treatment of chronic heart failure.

Enhanced resistance to permeability transition in interfibrillar cardiac mitochondria in dogs: effects of aging and long-term aldosterone infusion

Functional differences between subsarcolemmal and interfibrillar cardiac mitochondria (SSM and IFM) have been observed with aging and pathological conditions in rodents. Results are contradictory, and there is little information from large animal models. We assessed the respiratory function and resistance to mitochondrial permeability transition (MPT) in SSM and IFM from healthy young (1 yr) and old (8 yr) female beagles and in old beagles with hypertension and left ventricular (LV) wall thickening induced by 16 wk of aldosterone infusion. MPT was assessed in SSM and IFM by Ca(2+) retention and swelling. Healthy young and old beagles had similar mitochondrial structure, respiratory function, and Ca(2+)-induced MPT within SSM and IFM subpopulations. On the other hand, oxidative capacity and resistance to Ca(2+)-induced MPT were significantly greater in IFM compared with SSM in all groups. Old beagles treated with aldosterone had greater LV wall thickness and worse diastolic filling but normal LV chamber volume and systolic function. Treatment with aldosterone did not alter mitochondrial respiratory function but accelerated Ca(2+)-induced MPT in SSM, but not IFM, compared with healthy old and young beagles. In conclusion, in a large animal model, oxidative capacity and resistance to MPT were greater in IFM than in SSM. Furthermore, aldosterone infusion increased susceptibility to MPT in SSM, but not IFM. Together this suggests that SSM are less resilient to acute stress than IFM in the healthy heart and are more susceptible to the development of pathology with chronic stress.

Baroreflex activation for the treatment of heart failure

Autonomic dysregulation is a feature of heart failure (HF) characterized by sustained increase of sympathetic drive and by withdrawal of parasympathetic activity. Both maladaptations are independent predictors of poor long-term outcome in patients with HF. Considerable evidence exists that supports the use of pharmacologic agents that partially inhibit sympathetic activity as an effective long-term therapy for patients with HF; the classic example being the use of selective and nonselective β-adrenergic receptor blockers. In contrast, modulation of parasympathetic activation as potential therapy for HF has received only limited attention. This review discusses the results of recent preclinical animal studies that provide support for the possible use of baroreflex electrical stimulation, also known as baroreflex activation therapy (BAT), as a long-term therapeutic approach for the treatment of patients with chronic HF. In addition to exploring the effects of chronic BAT on left ventricular (LV) function and chamber remodeling, the review will also address the effects of long-term BAT on ventricular arrhythmias and on potential modifiers of the HF state that include maladaptations of both the nitric oxide and β-adrenergic receptor signal transduction pathways. The results of the preclinical studies conducted to date have shown that in dogs with advanced HF, monotherapy with BAT improves global LV systolic and diastolic function and partially reverses LV remodeling both globally and at cellular and molecular levels. In addition, BAT therapy was shown to markedly increase the threshold for lethal ventricular arrhythmias in dogs with chronic HF. These benefits of BAT support the continued exploration of this therapeutic modality for treating patients with chronic HF and those with increased risk of sudden cardiac death.

Electrical vagus nerve stimulation for the treatment of chronic heart failure

Autonomic dysregulation is a feature of chronic heart failure (HF) and is characterized by a sustained increase of sympathetic drive and by withdrawal of parasympathetic activity. Both sympathetic overdrive and increased heart rate are predictors of poor long-term outcome in patients with HF. Pharmacologic agents that partially inhibit sympathetic activity, such as beta-adrenergic receptor blockers, effectively reduce mortality and morbidity in patients with chronic HF. In contrast, modulation of parasympathetic activation as a potential therapy for HF has received only limited attention because of its inherent complex cardiovascular effects. This review examines results of experimental animal studies that provide support for the possible use of electrical vagus nerve stimulation (VNS) as a long-term therapy for the treatment of chronic HF. The review also addresses the effects of VNS on potential modifiers of the HF state, including proinflammatory cytokines, nitric oxide elaboration, and myocardial expression of gap junction proteins. Finally, the safety, feasibility, and efficacy trends of VNS in patients with advanced HF are reviewed.

Vagus nerve stimulation in experimental heart failure

Chronic heart failure (HF) is associated with autonomic dysregulation characterized by a sustained increase in sympathetic drive and by withdrawal of parasympathetic activity. Sympathetic overdrive and increased heart rate are predictors of poor long-term outcome in patients with HF. Considerable evidence exists that supports the use of pharmacologic agents that partially inhibit sympathetic activity as effective long-term therapy for patients with HF; the classic example is the wide use of selective and non-selective beta-adrenergic receptor blockers. In contrast, modulation of parasympathetic activation as potential therapy for HF has received only limited attention over the years given its complex cardiovascular effects. In this article, we review the results of recent experimental animal studies that provide support for the possible use of electrical Vagus nerve stimulation (VNS) as a long-term therapy for the treatment of chronic HF. In addition to exploring the effects of chronic VNS on left ventricular (LV) function, the review will also address the effects of VNS on potential modifiers of the HF state that include cytokine production and nitric oxide elaboration. Finally, we will briefly review other nerve stimulation approaches which is also currently under investigation as potential therapeutic modalities for treating chronic HF.

Myocardial transfection with naked DNA plasmid encoding hepatocyte growth factor prevents the progression of heart failure in dogs

This study examined the effects of localized intramyocardial injections of hepatocyte growth factor (HGF) naked DNA plasmid on the progression of left ventricular (LV) dysfunction and remodeling in dogs with moderate heart failure (HF). Twenty-one dogs with intracoronary microembolization-induced HF [LV ejection fraction (EF) = 35-40%] were randomized into three treatment groups, namely, high-dose HGF plasmid (4.0 mg, n = 7), low-dose HGF plasmid (0.4 mg, n = 7), and sham-operated controls treated with normal saline (n = 7). A total of 10-15 injections of HGF plasmid or saline were made directly into the anterior wall of LV. LV EF and end-systolic volume (ESV) were measured before randomization (pretreatment) and at the end of 3 mo of follow-up (posttreatment). Treatment effect (Δ) was calculated as the change from pre- to posttreatment. Protein expression of sarcoplasmic reticulum (SR) Ca(2+)-cycling proteins was determined in LV tissue obtained from the sites of HGF injection and remote areas. Low-dose HGF attenuated the decline in EF (ΔEF: -3 ± 1 vs. -8 ± 1%, P < 0.05) and the increase in ESV (ΔESV: 6 ± 2 vs. 10 ± 1 ml, P < 0.05) seen in control sham-operated dogs, whereas high-dose HGF significantly increased EF (ΔEF: 4 ± 1 vs. -8 ± 1%, P < 0.05) and prevented the increase in ΔESV (ESV: -1 ± 1 vs. 10 ± 1 ml, P < 0.05) compared with control dogs. Treatment with high- and low-dose HGF improved the expression of the SR Ca(2+)-cycling proteins compared with controls. In conclusion, regional intramyocardial injections of HGF naked DNA plasmid improve regional and global LV function and prevent progressive LV remodeling.

Chronic electrical stimulation of the carotid sinus baroreflex improves left ventricular function and promotes reversal of ventricular remodeling in dogs with advanced heart failure

BACKGROUND

Autonomic abnormalities exist in heart failure and contribute to disease progression. Activation of the carotid sinus baroreflex (CSB) has been shown to reduce sympathetic outflow and augment parasympathetic vagal tone. This study tested the hypothesis that long-term electric activation of the CSB improves left ventricular (LV) function and attenuates progressive LV remodeling in dogs with advanced chronic heart failure.

METHODS AND RESULTS

Studies were performed in 14 dogs with coronary microembolization-induced heart failure (LV ejection fraction ≈25%). Eight dogs were chronically instrumented for bilateral CSB activation using the Rheos System (CVRx Inc, Minneapolis, Minn) and 6 were not and served as controls. All dogs were followed for 3 months, and none received other background therapy. During follow-up, treatment with CSB increased LV ejection fraction 4.0±2.4% compared with a reduction in control dogs of −2.8±1.0% (P<0.05). Similarly, treatment with CSB decreased LV end-systolic volume -2.5±2.7 mL compared with an increase in control dogs of 6.7±2.9 mL (P<0.05). Compared with control, CSB activation significantly decreased LV end-diastolic pressure and circulating plasma norepinephrine, normalized expression of cardiac β(1)-adrenergic receptors, β-adrenergic receptor kinase, and nitric oxide synthase and reduced interstitial fibrosis and cardiomyocyte hypertrophy.

CONCLUSIONS

In dogs with advanced heart failure, CSB activation improves global LV function and partially reverses LV remodeling both globally and at cellular and molecular levels.

Effects of repeated maprotiline and fluoxetine treatment on gene expression of catecholamine synthesizing enzymes in adrenal medulla of unstressed and stressed rats

1 Repeated maprotiline (a noradrenaline reuptake inhibitor) and fluoxetine (a serotonin reuptake inhibitor) treatment on gene expression of catecholamine biosynthetic enzymes were examined in adrenal medulla of unstressed control and chronic unpredictable mild stressed rats. 2 Maprotiline did not change gene expression of catecholamine biosynthetic enzymes in control and stressed rats. 3 Fluoxetine increased gene expression of tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH), but did not phenylethanolamine N-methyltransferase in both unstressed and chronic unpredictable mild stressed animals. 4 In conclusion, we have demonstrated that repeated administration of fluoxetine enhanced gene transcription of TH and DBH and subsequently stimulates noradrenaline synthesis in adrenal medulla of control and stressed rats.

Effects of adiponectin deficiency on structural and metabolic remodeling in mice subjected to pressure overload

Recent data suggest adiponectin, an adipocyte-derived hormone, affects development of heart failure in response to hypertension. Severe short-term pressure overload [1-3 wk of transverse aortic constriction (TAC)] in adiponectin(-/-) mice causes greater left ventricle (LV) hypertrophy than in wild-type (WT) mice, but conflicting results are reported regarding LV remodeling, with either increased or decreased LV end diastolic volume compared with WT mice. Here we assessed the effects of prolonged TAC on LV hypertrophy and remodeling. WT and adiponectin(-/-) mice were subjected to TAC and maintained for 6 wk. Regardless of strain, TAC induced similar LV hypertrophy ( approximately 70%) and upregulation of mRNA for heart failure marker genes. However, LV chamber size was dramatically different, with classic LV dilation in WT TAC mice but concentric LV hypertrophy in adiponectin(-/-) mice. LV end diastolic and systolic volumes were lower and ejection fraction higher in adiponectin(-/-) TAC mice compared with WT, indicating that adiponectin deletion prevented LV remodeling and deterioration in systolic function. The activities of marker enzymes of mitochondrial oxidative capacity were reduced in WT TAC mice by approximately 35%, whereas enzyme activities were maintained at sham levels in adiponectin(-/-) TAC mice. In conclusion, in WT mice, long-term pressure overload caused dilated LV hypertrophy accompanied by decreased activity of mitochondrial oxidative enzymes. Although adiponectin deletion did not affect LV hypertrophy, it prevented LV chamber remodeling and preserved mitochondrial oxidative capacity, suggesting that adiponectin plays a permissive role in mediating changes in cardiac structure and metabolism in response to pressure overload.

Effect of immobilization stress on gene expression of catecholamine biosynthetic enzymes in heart auricles of socially isolated rats

Chronic stress is associated with the development of cardiovascular diseases. The sympathoneural system plays an important role in the regulation of cardiac function both in health and disease. In the present study, the changes in gene expression of the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) and protein levels in the right and left heart auricles of naive control and long-term (12 weeks) socially isolated rats were investigated by Taqman RT-PCR and Western blot analysis. The response of these animals to additional immobilization stress (2 h) was also examined. Long-term social isolation produced a decrease in TH mRNA level in left auricles (about 70%) compared to the corresponding control. Expression of the DBH gene was markedly decreased both in the right (about 62%) and left (about 81%) auricles compared to the corresponding control, group-maintained rats, whereas PNMT mRNA levels remained unchanged. Exposure of group-housed rats to acute immobilization for 2 h led to a significant increase of mRNA levels of TH (about 267%), DBH (about 37%) and PNMT (about 60%) only in the right auricles. Additional 2-h immobilization of individually housed rats did not affect gene expression of these enzymes in either the right or left auricle. Protein levels of TH, DBH and PNMT in left and right heart auricles were unchanged either in both individually housed and immobilized rats. The unchanged mRNA levels of the enzymes examined after short-term immobilization suggest that the catecholaminergic system of the heart auricles of animals previously exposed to chronic psychosocial stress was adapted to maintain appropriate cardiovascular homeostasis.

Darbepoetin-alpha prevents progressive left ventricular dysfunction and remodeling in nonanemic dogs with heart failure

In anemic patients with heart failure (HF), erythropoietin-type drugs can elicit clinical improvement. This study examined the effects of chronic monotherapy with darbepoetin-alpha (DARB) on left ventricular (LV) function and remodeling in nonanemic dogs with advanced HF. HF [LV ejection fraction (EF) approximately 25%] was produced in 14 dogs by intracoronary microembolizations. Dogs were randomized to once a week subcutaneous injection of DARB (1.0 microg/kg, n=7) or to no therapy (HF, n=7). All procedures were performed during cardiac catheterization under general anesthesia and under sterile conditions. LV end-diastolic volume (EDV), end-systolic volume (ESV), and EF were measured before the initiation of therapy and at the end of 3 mo of therapy. mRNA and protein expression of caspase-3, hypoxia inducible factor-1alpha, and the bone marrow-derived stem cell marker c-Kit were determined in LV tissue. In HF dogs, EDV and ESV increased and EF decreased after 3 mo of followup. Treatment with DARB prevented the increase in EDV, decreased ESV, and increased EF. DARB therapy also normalized the expression of HIF-1alpha and active caspase-3 and enhanced the expression of c-Kit. We conclude that chronic monotherapy with DARB prevents progressive LV dysfunction and dilation in nonanemic dogs with advanced HF. These results suggest that DARB elicits beneficial effects in HF that are independent of the presence of anemia.

High-sugar diets increase cardiac dysfunction and mortality in hypertension compared to low-carbohydrate or high-starch diets

OBJECTIVE

Sugar consumption affects insulin release and, in hypertension, may stimulate cardiac signaling mechanisms that accelerate left ventricular hypertrophy and the development of heart failure. We investigated the effects of high-fructose or sucrose diets on ventricular function and mortality in hypertensive Dahl salt-sensitive rats.

METHODS

Rats were fed chows that were either high starch (70% starch, 10% fat by energy), high fat (20% carbohydrates, 60% fat), high fructose (61% fructose, 9% starch, 10% fat), or high sucrose (61% sucrose, 9% starch, 10% fat). Hypertension was induced by adding 6% salt to the chow (n = 8-11/group).

RESULTS

After 8 weeks of treatment, systolic blood pressure and left ventricular mass were similarly increased in all rats that were fed high-salt diets. Hypertension caused a switch in mRNA myosin heavy chain isoform from alpha to beta, and this effect was greater in the high-salt sucrose and fructose groups than in starch and fat groups. The cardiac mRNA for atrial natriuretic factor was also increased in all high-salt groups compared to respective controls, with the increase being significantly greater in the hypertensive sucrose fed group. Mortality was greater in the sucrose group (44%) compared to all the other hypertensive groups (12-18%), as was cardiomyocyte apoptosis. Left ventricular ejection fraction was lower in the high-salt sucrose group, which was due to an increase in end-systolic volume, and not increased end-diastolic volume.

CONCLUSION

Diets high in sugar accelerated cardiac systolic dysfunction and mortality in hypertension compared to either a low-carbohydrate/high-fat or high-starch diet.

Atenolol is inferior to metoprolol in improving left ventricular function and preventing ventricular remodeling in dogs with heart failure

OBJECTIVES

beta-Blockers are standard therapy for patients with heart failure (HF). This study compared the effects of chronic monotherapy with 2 different beta(1)-selective adrenoceptor blockers, namely atenolol and metoprolol succinate, on left ventricular (LV) function and remodeling in dogs with coronary microembolization-induced HF [LV ejection fraction (EF) 30-40%].

METHODS

Twenty HF dogs were randomized to 3 months of therapy with atenolol (50 mg once daily, n = 6), metoprolol succinate (100 mg, once daily, n = 7) or to no therapy (control, n = 7). LV EF and volumes were measured before initiating therapy and after 3 months of therapy. The change (Delta) in EF and volumes between measurements before and after therapy was calculated and compared among study groups.

RESULTS

In controls, EF decreased and end-systolic volume increased. Atenolol prevented the decrease in EF and the increase in ESV. In contrast, metoprolol succinate significantly increased EF and decreased end-systolic volume. DeltaEF was significantly higher and Deltaend-systolic volume significantly lower in metoprolol succinate-treated dogs compared to atenolol-treated dogs (EF: 6.0 +/- 0.86% vs. 0.8 +/- 0.85%, p < 0.05; end-systolic volume: -4.3 +/- 0.81 ml vs. -1 +/- 0.52 ml, p <0.05).

CONCLUSIONS

In HF dogs, chronic therapy with atenolol does not elicit the same LV function and remodeling benefits as those achieved with metoprolol succinate.

Ranolazine combined with enalapril or metoprolol prevents progressive LV dysfunction and remodeling in dogs with moderate heart failure

Acute intravenous infusion of ranolazine (Ran), an anti-ischemic/antiangina drug, was previously shown to improve left ventricular (LV) ejection fraction (EF) without a concomitant increase in myocardial oxygen consumption in dogs with chronic heart failure (HF). This study examined the effects of treatment with Ran alone and in combination with metoprolol (Met) or enalapril (Ena) on LV function and remodeling in dogs with HF. Dogs (n = 28) with microembolization-induced HF were randomized to 3 mo oral treatment with Ran alone [375 mg twice daily (bid); n = 7], Ran (375 mg bid) in combination with Met tartrate (25 mg bid; n = 7), Ran (375 mg bid) in combination with Ena (10 mg bid; n = 7), or placebo (PL; Ran vehicle bid; n = 7). Ventriculographic measurements of LV end-diastolic volume (EDV) and end-systolic volume (ESV) and LV EF were obtained before treatment and after 3 mo of treatment. In PL-treated dogs, EDV and ESV increased significantly. Ran alone prevented the increase in EDV and ESV seen in the PL group and significantly increased EF, albeit modestly, from 35 +/- 1% to 37 +/- 2%. When combined with either Ena or Met, Ran prevented the increase in EDV, significantly decreased ESV, and markedly increased EF compared with those of PL. EF increased from 35 +/- 1% to 40 +/- 1% with Ran + Ena and from 34 +/- 1% to 41 +/- 1% with Ran + Met. Ran alone or in combination with Ena or Met was also associated with beneficial effects at the cellular level on histomorphometric parameters such as hypertrophy, fibrosis, and capillary density as well as the expression for pathological hypertrophy and Ca2+ cycling genes. In conclusion, Ran prevented progressive LV dysfunction and global and cellular myocardial remodeling, and Ran in combination with Ena or Met improved LV function beyond that observed with Ran alone.

Chronic Monotherapy With Rosuvastatin Prevents Progressive Left Ventricular Dysfunction and Remodeling in Dogs With Heart Failure

OBJECTIVES

This study examined the effects of long-term monotherapy with rosuvastatin (RSV) on the progression of left ventricular (LV) dysfunction and remodeling in dogs with heart failure (HF).

BACKGROUND

3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors or "statins" possess other noncholesterol-lowering properties that include inhibiting proinflammatory cytokines, attenuating LV hypertrophy, and stimulating the release of bone marrow-derived stem cells (BMSCs).

METHODS

Twenty-one dogs with microembolization-induced HF were randomized to 3 months oral monotherapy with low-dose (LD) RSV (0.5 mg/kg once daily, n = 7), high-dose (HD) RSV (3.0 mg/kg once daily, n = 7), or to no therapy (control group, n = 7). The change (Delta) from pre- to post-therapy (treatment effect) in LV end-diastolic volume (EDV) and end-systolic volume (ESV) and ejection fraction (EF) was measured. Protein level of tumor necrosis factor (TNF)-alpha in LV tissue and the number of circulating Sca-1-positive BMSCs was also determined. Blood and LV tissue from 6 normal dogs was obtained and used for comparison.

RESULTS

There were no differences in DeltaEDV, DeltaESV, and DeltaEF between control group and LD RSV. In contrast, DeltaEDV and DeltaESV were significantly lower, and DeltaEF was significantly higher in HD RSV compared with control group. High-dose, but not LD, RSV also normalized protein levels of TNF-alpha and was associated with a significant increase in the number of circulating BMSCs.

CONCLUSIONS

In dogs with HF, chronic therapy with HD RSV prevents progressive LV dysfunction and dilation. This benefit may be partly derived from normalization of TNF-alpha expression and partly from increased mobilization of BMSCs.

Myocardial substrate metabolism in the normal and failing heart

The alterations in myocardial energy substrate metabolism that occur in heart failure, and the causes and consequences of these abnormalities, are poorly understood. There is evidence to suggest that impaired substrate metabolism contributes to contractile dysfunction and to the progressive left ventricular remodeling that are characteristic of the heart failure state. The general concept that has recently emerged is that myocardial substrate selection is relatively normal during the early stages of heart failure; however, in the advanced stages there is a downregulation in fatty acid oxidation, increased glycolysis and glucose oxidation, reduced respiratory chain activity, and an impaired reserve for mitochondrial oxidative flux. This review discusses 1) the metabolic changes that occur in chronic heart failure, with emphasis on the mechanisms that regulate the changes in the expression of metabolic genes and the function of metabolic pathways; 2) the consequences of these metabolic changes on cardiac function; 3) the role of changes in myocardial substrate metabolism on ventricular remodeling and disease progression; and 4) the therapeutic potential of acute and long-term manipulation of cardiac substrate metabolism in heart failure.

[Strategies for perioperative sympatho-modulation]

Despite the growing evidence for the efficacy of different sympatho-modulatory therapies to lower perioperative cardiac morbidity and mortality, such therapeutic strategies are rather infrequently used in daily clinical practice. Most physicians involved in perioperative medicine are aware of the increasing literature related to this topic, but only few comply with current clinical practice guidelines even in the absence of contraindications. This review discusses possible explanations for this reluctance and again summarizes the basic and clinical principles of current sympatho-modulatory therapies including alpha(2)-agonism, beta-adrenergic antagonism, and regional anesthetic techniques in modern anesthetic practice. In addition, the emerging perioperative concept of a patient-tailored individualized pharmacotherapy based on "gene profiling", particularly the adrenergic polymorphisms, is discussed.

Moderate severity heart failure does not involve a downregulation of myocardial fatty acid oxidation

Recent human and animal studies have demonstrated that in severe end-stage heart failure (HF), the cardiac muscle switches to a more fetal metabolic phenotype, characterized by downregulation of free fatty acid (FFA) oxidation and an enhancement of glucose oxidation. The goal of this study was to examine myocardial substrate metabolism in a model of moderate coronary microembolization-induced HF. We hypothesized that during well-compensated HF, FFA oxidation would predominate as opposed to a more fetal metabolic phenotype of greater glucose oxidation. Cardiac substrate uptake and oxidation were measured in normal dogs ( n = 8) and in dogs with microembolization-induced HF ( n = 18, ejection fraction = 28%) by infusing three isotopic tracers ([9,10-3H]oleate, [U-14C]glucose, and [1-13C]lactate) in anesthetized open-chest animals. There were no differences in myocardial substrate metabolism between the two groups. The total activity of pyruvate dehydrogenase, the key enzyme regulating myocardial pyruvate oxidation (and hence glucose and lactate oxidation) was not affected by HF. We did not observe any difference in the activity of carnitine palmitoyl transferase I (CPT-I) and its sensitivity to inhibition by malonyl-CoA between groups; however, malonyl-CoA content was decreased by 22% with HF, suggesting less in vivo inhibition of CPT-I activity. The differences in malonyl-CoA content cannot be explained by changes in the Michaelis-Menten constant and maximal velocity for malonyl-CoA decarboxylase because neither were affected by HF. These results support the concept that there is no decrease in fatty acid oxidation during compensated HF and that the downregulation of fatty acid oxidation enzymes and the switch to carbohydrate oxidation observed in end-stage HF is only a late-stage phenomemon.

Reverse Remodeling of the Failing Ventricle: Surgical Intervention With the Acorn Cardiac Support Device

Preclincial studies have shown that an innovative meshlike cardiac support device (CorCap, Acorn Cardiovascular, Inc., St. Paul, MN) can provide end diastolic support to reduce mechanical stress, improve function, and reverse cardiac remodeling. The CorCap device has been implanted worldwide in more than 130 patients with dilated cardiomyopathy (idiopathic or ischemic), with or without concomitant cardiac surgery. A series of 48 patients was implanted in initial safety and feasibility studies (33 received concomitant cardiac surgery, 15 patients received the CorCap device only). At implant, 33 patients were in New York Heart Association functional class III, 11 in class II, and four in class IV. There were no device-related intraoperative complications, deaths, or adverse events. Eight early and nine late deaths occurred during follow-up extending to 18-24 months. During follow-up, chamber dimensions decreased, and ejection fraction and New York Heart Association functional class improved. The CorCap device is correlated with improvements in patient functional status. Randomized clinical trials are underway in Europe, Australia, and North America.

Long-term treatment with low-dose, but not high-dose, guanethidine improves ventricular function and survival of rats with heart failure after myocardial infarction

OBJECTIVES

We sought to evaluate the effects of various doses of guanethidine, a sympathoinhibitory drug, on ventricular function and survival in chronic heart failure (CHF) after myocardial infarction (MI) in rats.

BACKGROUND

Direct inhibition of sympathetic outflow by a sympathoinhibitory drug might be an effective approach to therapy of CHF. However, recent clinical trials suggest that excessive suppression of sympathetic activity has an adverse effect on outcome. It remains unclear whether the beneficial effects of the sympathoinhibitory drug would be modified by its dosage.

METHODS

Three doses of guanethidine (low-dose [LG], 1 mg/kg/day; medium-dose, 3 mg/kg/day; high-dose, 10 mg/kg/day) were administered via an osmotic mini-pump for 4 weeks. Hemodynamics, left ventricular (LV) diameters, plasma and myocardial norepinephrine (NE) levels, and survival were determined for four weeks after MI.

RESULTS

As compared with MI rats receiving vehicle, LG suppressed LV dilation (9.2 +/- 0.9 mm vs. 11.0 +/- 0.8 mm, p < 0.05) and improved LV fractional shortening (25.0 +/- 4.5% vs. 16.4 +/- 4.7%, p < 0.05) in association with a reduction of plasma NE levels (520 +/- 250 pg/ml vs. 1,000 +/- 570 pg/ml, p < 0.05), but not with a significant reduction of noninfarcted myocardial NE levels (154 +/- 71 ng/g vs. 207 +/- 71 ng/g). Low-dose guanethidine reduced 24-h (6%) and 28-day mortality (6%), as compared with untreated MI rats (36% and 52%, respectively). High-dose guanethidine also reduced 24-h mortality (12%) but increased 28-day mortality (91%), in association with a depletion of myocardial NE. Medium-dose guanethidine had no beneficial effects on LV hemodynamics or long-term survival.

CONCLUSIONS

These results indicate that the dosage of the sympathoinhibitory drug might be quite important for the treatment of CHF.

Adrenocorticotropic hormone (MC-2) receptor mRNA is expressed in rat sympathetic ganglia and up-regulated by stress

Stress triggered cardiovascular disorders are associated with elevated activity of the sympathetic nervous system, the major source of elevated plasma norepinephrine levels. Our previous studies revealed that administration of adrenocorticotropic hormone (ACTH) increases the gene expression of norepinephrine biosynthetic enzymes and several neuropeptides in rat sympathetic ganglia as much as stress. Here, we examine whether an ACTH-responsive receptor is expressed in rat superior cervical (SCG) and stellate ganglia (StG). Using reverse transcriptase-polymerase chain reaction (RT-PCR) we found expression of MC-2 receptor mRNA in these ganglia. Identical DNA fragments were amplified with mRNA from SCG, StG or from adrenal cortex. Sequencing revealed extensive homology to published sequences of mouse and human MC-2 receptor. Real time PCR was used to quantitate MC-2 receptor mRNA levels in the SCG under basal conditions and following immobilization stress. Immobilization stress triggered a large increase in MC-2 receptor mRNA in SCG. The results provide the first evidence that rat sympathetic ganglia express MC-2 receptor gene and are a target tissue for the peripheral actions of ACTH in response to stress.

Surgical management of heart failure: an overview

Cardiac transplantation remains the gold standard of surgical therapies for advanced and end-stage heart failure. However, this very limited option trades one disease for another and can benefit only a small minority of patients. Heart failure is currently considered secondary to a structural increase in ventricular chamber volume or remodeling. Surgical therapies formerly contraindicated for the failing heart, as well as new therapies, can successfully affect ventricular remodeling and improve cardiac function. Surgical revascularization for patients with ejection fractions <20% is becoming common. Mitral valve repair is being explored, with surprisingly low operative mortality and encouraging intermediate results. Direct surgical approaches to restoring normal geometry and size to failing hearts, such as left ventricular reduction (Batista procedure), endoventricular patch plasty (Dor procedure), cardiomyoplasty, and prosthetic external constraints are under clinical investigation. Developments in mechanical assist therapy and a new generation of implantable intracorporeal assist devices are also discussed.

Left ventricular splints and wraps for end-stage heart failure: a new approach in the new millennium

The epidemic of heart failure and its subsequent effect on public health policy is escalating. Cardiac transplantation continues to be limited by the shortage of donor organs, and the current generation of mechanical circulatory support devices has not yet approached the goal of destination therapy. A better understanding of the role of left ventricular remodeling in the development of heart failure has resulted in novel surgical therapies and devices that may reverse or retard the remodeling process.

Reduced synthesis of NO causes marked alterations in myocardial substrate metabolism in conscious dogs

To test whether the acute reduction of nitric oxide (NO) synthesis causes changes in cardiac substrate metabolism and in the activity of key enzymes of fatty acid and glucose oxidation, we blocked NOS by giving N(omega)-nitro-L-arginine methyl ester (L-NAME; 35 mg/kg iv two times) to nine chronically instrumented dogs. [3H]oleate, [14C]glucose, and [13C]lactate were infused to measure the rate of cardiac substrate uptake and oxidation. Glyceraldehyde-3-phosphate dehydrogenase, acetyl-CoA carboxylase, and malonyl-CoA decarboxylase activities were measured in myocardial biopsies. In eight control dogs, ANG II was infused (20-40 ng x kg(-1) x min(-1)) to mimic the hemodynamic effects of L-NAME. After L-NAME, significant changes occurred for fatty acid oxidation (from 9.8 +/- 0.8 to 7.1 +/- 1.2 micromol/min), glucose uptake (from 12.9 +/- 5.5 to 45.0 +/- 14.2 micromol/min), and oxidation (from 4.4 +/- 1.2 to 19.9 +/- 2.3 micromol/min). ANG caused only a significantly lower increase in glucose oxidation. Lactate uptake increased by more than twofold in both groups. The enzyme activities did not differ significantly between the two groups. In conclusion, the acute inhibition of NO synthesis causes marked metabolic alterations that do not involve key rate-controlling enzymes of fatty acid oxidation nor glyceraldehyde-3-phosphate dehydrogenase.

New and emerging pharmacological strategies in the management of chronic heart failure

Chronic heart failure is a complex syndrome involving the activation of multiple cellular, metabolic and neurohumoral pathways following the initial myocardial insult. Because of the complexity of the disease, strategies targeting these multiple systems involved in disease progression are required to maximise the therapeutic benefits of intervention. To this end, there are a number of approaches currently under active evaluation. These include the inhibition of additional neurohormonal vasoconstrictor systems (e.g. endothelin and vasopressin systems), cytokine antagonists (e.g. agents that block tumour necrosis factor-alpha activity), agents that favourably modulate extracellular matrix (e.g. matrix metalloprotease inhibitors) and agents that augment natriuretic peptides.