Effects of myocardial alpha 1-adrenergic receptor stimulation and blockade on contractility in humans

Ultrasound dilution cardiac output and echocardiography findings in anesthetized mature alpacas (Vicugna pacos) during normotension, hypotension and hypertension

Alpacas (Vicugna pacos) have physiologic adaptations to live at high altitude. These adaptations may result in unexpected responses to changes in cardiac performance and blood pressure during general anesthesia. There are few studies evaluating cardiovascular variables in anesthetized alpacas. The purpose of this study was to report cardiovascular performance in anesthetized mature alpacas during normotension, hypotension, and hypertension using ultrasound dilution and echocardiography. Six adult alpacas, 3 females and 3 castrated males, weighing 62.6 to 88.7 kg were anesthetized and maintained with isoflurane and placed in right lateral recumbency. Each alpaca underwent ultrasound dilution and echocardiography measurements during three cardiovascular phases, normotension, hypotension via increased isoflurane concentration, and hypertension via phenylephrine infusion. Variables were analyzed with a Friedman test and a post hoc Dunn's test when significant. A p < 0.05 was used for significance. Cardiac output, cardiac index, systemic vascular resistance, stroke volume, total ejection fraction, left ventricular internal diameter during diastole, and total stroke volume indexed to body weight were greater for hypertension compared to hypotension. Total ejection fraction, stroke volume, and left ventricular ejection time were greater for hypertions compared to normotension. There was no difference between ultrasound dilution and echocardiography determined cardiac output measurements within each cardiovascular phase. Phenylephrine appeared to have increased ventricular performance and/or increased preload in anesthetized, mature alpacas. For detecting change in cardiovascular status in anesthetized alpacas, ultrasound dilution and echocardiography may be useful.

Adrenergic Receptor Regulation of Mitochondrial Function in Cardiomyocytes

ABSTRACT

Adrenergic receptors (ARs) are G protein-coupled receptors that are stimulated by catecholamines to induce a wide array of physiological effects across tissue types. Both α1- and β-ARs are found on cardiomyocytes and regulate cardiac contractility and hypertrophy through diverse molecular pathways. Acute activation of cardiomyocyte β-ARs increases heart rate and contractility as an adaptive stress response. However, chronic β-AR stimulation contributes to the pathobiology of heart failure. By contrast, mounting evidence suggests that α1-ARs serve protective functions that may mitigate the deleterious effects of chronic β-AR activation. Here, we will review recent studies demonstrating that α1- and β-ARs differentially regulate mitochondrial biogenesis and dynamics, mitochondrial calcium handling, and oxidative phosphorylation in cardiomyocytes. We will identify potential mechanisms of these actions and focus on the implications of these findings for the modulation of contractile function in the uninjured and failing heart. Collectively, we hope to elucidate important physiological processes through which these well-studied and clinically relevant receptors stimulate and fuel cardiac contraction to contribute to myocardial health and disease.

α1-adrenergic stimulation increases ventricular action potential duration in the intact mouse heart

The role of α1-adrenergic receptors (α-ARs) in the regulation of myocardial function is less well-understood than that of β-ARs. Previous reports in the mouse heart have described that α1-adrenergic stimulation shortens action potential duration in isolated cells or tissues, in contrast to prolongation of the action potential reported in most other mammalian hearts. It has since become appreciated, however, that the mouse heart exhibits marked variation in inotropic response to α1-adrenergic stimulation between ventricles and even individual cardiomyocytes. We investigated the effects of α1-adrenergic stimulation on action potential duration at 80% of repolarization in the right and left ventricles of Langendorff-perfused mouse hearts using optical mapping. In hearts under β-adrenergic blockade (propranolol), phenylephrine or noradrenaline perfusion both increased action potential duration in both ventricles. The increased action potential duration was partially reversed by subsequent perfusion with the α-adrenergic antagonist phentolamine (1 μmol L−1). These data show that α1-receptor stimulation may lead to a prolonging of action potential in the mouse heart and thereby refine our understanding of how action potential duration adjusts during sympathetic stimulation.

Cardiac α1A-adrenergic receptors: emerging protective roles in cardiovascular diseases

α1-Adrenergic receptors (ARs) are catecholamine-activated G protein-coupled receptors (GPCRs) that are expressed in mouse and human myocardium and vasculature, and play essential roles in the regulation of cardiovascular physiology. Though α1-ARs are less abundant in the heart than β1-ARs, activation of cardiac α1-ARs results in important biologic processes such as hypertrophy, positive inotropy, ischemic preconditioning, and protection from cell death. Data from the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) indicate that nonselectively blocking α1-ARs is associated with a twofold increase in adverse cardiac events, including heart failure and angina, suggesting that α1-AR activation might also be cardioprotective in humans. Mounting evidence implicates the α1A-AR subtype in these adaptive effects, including prevention and reversal of heart failure in animal models by α1A agonists. In this review, we summarize recent advances in our understanding of cardiac α1A-ARs.

The cardiac work-loop technique: An in vitro model for identifying and profiling drug-induced changes in inotropy using rat papillary muscles

The cardiac work-loop technique closely mimics the intrinsic in vivo movement and characteristics of cardiac muscle function. In this study, six known inotropes were profiled using the work-loop technique to evaluate the potential of this method to predict inotropy. Papillary muscles from male Sprague-Dawley rats were mounted onto an organ bath perfused with Krebs-Henseleit buffer. Following optimisation, work-loop contractions were performed that included an initial stabilisation period followed by vehicle control or drug administration. Six known inotropes were tested: digoxin, dobutamine, isoprenaline, flecainide, verapamil and atenolol. Muscle performance was evaluated by calculating power output during work-loop contraction. Digoxin, dobutamine and isoprenaline caused a significant increase in power output of muscles when compared to vehicle control. Flecainide, verapamil and atenolol significantly reduced power output of muscles. These changes in power output were reflected in alterations in work loop shapes. This is the first study in which changes in work-loop shape detailing for example the activation, shortening or passive re-lengthening have been linked to the mechanism of action of a compound. This study has demonstrated that the work-loop technique can provide an important novel method with which to assess detailed mechanisms of drug-induced effects on cardiac muscle contractility.

Vasoactive Agent Use in Septic Shock: Beyond First-Line Recommendations

Septic shock is a life-threatening disorder associated with high mortality rates requiring rapid identification and intervention. Vasoactive agents are often required to maintain goal hemodynamics and preserve tissue perfusion. However, guidance regarding the proper administration of adjunct agents for the management of septic shock is limited in patients who are refractory to norepinephrine. This review summarizes vasopressor agents and describes the nuanced application of these agents in patients with septic shock, specifically focusing on clinical scenarios with limited guidance including patients who are nonresponsive to first-line agents and individuals with mixed shock states, tachyarrhythmias, obesity, valvular abnormalities, or other comorbid conditions.

Successful Cardiopulmonary Resuscitation in a Sevoflurane Anaesthetized Horse That Suffered Cardiac Arrest at Recovery

A 17-year-old mare undergoing dental surgery suffered a cardiac arrest while being transferred from the surgical theatre to the recovery box. This complication was diagnosed early, thus allowing a prompt start to the cardiopulmonary resuscitation maneuvers. External thoracic compressions, intermittent positive pressure ventilation, and adrenaline administration were at the core of this successful resuscitation. Although it was not possible to confirm the cause of cardiac arrest in this horse, a Bezold-Jarisch reflex due to potential decrease on venous return because of postural change and drug interactions was hypothesized. Based on this report, it appears advisable to smoothly change the position of anaesthetized patient; furthermore, the administration of drugs affecting cardiovascular hemodynamics or sympatho-vagal balance to animals while changing their recumbency should be avoided.

Effects of dobutamine hydrochloride on cardiovascular function in horses anesthetized with isoflurane with or without acepromazine maleate premedication

OBJECTIVE To determine the effects of acepromazine maleate premedication on cardiovascular function before and after infusion of dobutamine hydrochloride for 30 minutes in isoflurane-anesthetized horses. ANIMALS 6 healthy adult horses. PROCEDURES Each horse was anesthetized once following premedication with acepromazine (0.02 mg/kg, IV) administered 30 minutes prior to anesthetic induction (ACP+ treatment) and once without premedication (ACP- treatment). Anesthesia was induced with IV administration of xylazine hydrochloride (0.8 mg/kg), ketamine hydrochloride (2.2 mg/kg), and diazepam (0.08 mg/kg). Horses were positioned in right lateral recumbency, and anesthesia was maintained via inhalation of isoflurane delivered in oxygen. End-tidal isoflurane concentration was adjusted to achieve a target mean arterial blood pressure of 60 mm Hg (interquartile range [25th to 75th percentile], 57 to 63 mm Hg) for at least 15 minutes. Cardiac index, oxygen delivery index, and femoral arterial blood flow indices were determined 60 minutes after anesthetic induction (baseline). Dobutamine was then infused to achieve a target mean arterial blood pressure of 80 mm Hg (interquartile range, 76 to 80 mm Hg). Data collection was repeated 30 minutes after the start of dobutamine infusion for comparison with baseline values. RESULTS Complete data sets were available from 5 of the 6 horses. Dobutamine administration resulted in significant increases in oxygen delivery and femoral arterial blood flow indices but no significant change in cardiac index for each treatment. However, at baseline or 30 minutes after the start of dobutamine infusion, findings for the ACP+ and ACP- treatments did not differ. CONCLUSIONS AND CLINICAL RELEVANCE In isoflurane-anesthetized horses, dobutamine administration increased oxygen delivery and femoral arterial blood flow indices, but these changes were unaffected by premedication with acepromazine.

Effects of commonly used inotropes on myocardial function and oxygen consumption under constant ventricular loading conditions

Inotropic medications are routinely used to increase cardiac output and arterial blood pressure during critical illness. However, few comparative data exist between these medications, particularly independent of their effects on venous capacitance and systemic vascular resistance. We hypothesized that an isolated working heart model that maintained constant left atrial pressure and aortic blood pressure could identify load-independent differences between inotropic medications. In an isolated heart preparation, the aorta and left atrium of Sprague Dawley rats were cannulated and placed in working mode with fixed left atrial and aortic pressure. Hearts were then exposed to common doses of a catecholamine (dopamine, epinephrine, norepinephrine, or dobutamine), milrinone, or triiodothyronine (n = 10 per dose per combination). Cardiac output, contractility (dP/dtmax), diastolic performance (dP/dtmin and tau), stroke work, heart rate, and myocardial oxygen consumption were compared during each 10-min infusion to an immediately preceding baseline. Of the catecholamines, dobutamine increased cardiac output, contractility, and diastolic performance more than clinically equivalent doses of norepinephrine (second most potent), dopamine, or epinephrine (P < 0.001). The use of triiodothyronine and milrinone was not associated with significant changes in cardiac output, contractility or diastolic function, either alone or added to a baseline catecholamine infusion. Myocardial oxygen consumption was closely related to dP/dtmax (r(2) = 0.72), dP/dtmin (r(2) = 0.70), and stroke work (r(2) = 0.53). In uninjured, isolated working rodent hearts under constant ventricular loading conditions, dobutamine increased contractility and cardiac output more than clinically equivalent doses of norepinephrine, dopamine, and epinephrine; milrinone and triiodothyronine did not have significant effects on contractility.

Overexpression of Cardiomyocyte α1A-Adrenergic Receptors Attenuates Postinfarct Remodeling by Inducing Angiogenesis Through Heterocellular Signaling

OBJECTIVE

Stimulation of cardiac α1A-adrenergic receptors (α1A-AR) has been proposed for treatment of heart failure, since it increases myocardial contractility. We investigated a different mechanism, induction of angiogenesis.

APPROACH AND RESULTS

Four to 6 weeks after permanent coronary artery occlusion, transgenic rats with cardiomyocyte-specific α1A-adrenergic receptor overexpression had less remodeling than their nontransgenic littermates, with less fibrosis, hypertrophy and lung weight, and preserved left ventricular ejection fraction and wall stress (all P<0.05). Coronary blood flow, measured with microspheres, increased in the infarct zone in transgenic rats compared with nontransgenic littermates (1.4±0.2 versus 0.5±0.08 mL min(-1) g(-1); P<0.05), which is consistent with angiogenesis, as reflected by a 20% increase in capillary density in the zone adjacent to the infarct. The question arose, how does transgenic overexpression of a gene in cardiomyocytes induce angiogenesis? We identified a paracrine mechanism, whereby vascular endothelial growth factor-A mRNA and protein were increased in isolated transgenic cardiomyocytes and also by nontransgenic littermate cardiomyocytes treated with an α1A-agonist, resulting in angiogenesis. Conditioned medium from cultured cardiomyocytes treated with an α1A agonist enhanced human umbilical vein endothelial cell tubule formation, which was blocked by an anti-vascular endothelial growth factor-A antibody. Moreover, improved cardiac function, blood flow, and increased capillary density after chronic coronary artery occlusion in transgenic rats were blocked by either a mitogen ERK kinase (MEK) or a vascular endothelial growth factor-A inhibitor.

CONCLUSION

Cardiomyocyte-specific overexpression of the α1A-adrenergic receptors resulted in enhanced MEK-dependent cardiomyocyte vascular endothelial growth factor-A expression, which stimulates angiogenesis via a paracrine mechanism involving heterocellular cardiomyocyte/endothelial cell signaling, protecting against remodeling and heart failure after chronic coronary artery occlusion.

Alpha-1-adrenergic receptors in heart failure: the adaptive arm of the cardiac response to chronic catecholamine stimulation

Alpha-1-adrenergic receptors (ARs) are G protein-coupled receptors activated by catecholamines. The alpha-1A and alpha-1B subtypes are expressed in mouse and human myocardium, whereas the alpha-1D protein is found only in coronary arteries. There are far fewer alpha-1-ARs than beta-ARs in the nonfailing heart, but their abundance is maintained or increased in the setting of heart failure, which is characterized by pronounced chronic elevation of catecholamines and beta-AR dysfunction. Decades of evidence from gain and loss-of-function studies in isolated cardiac myocytes and numerous animal models demonstrate important adaptive functions for cardiac alpha-1-ARs to include physiological hypertrophy, positive inotropy, ischemic preconditioning, and protection from cell death. Clinical trial data indicate that blocking alpha-1-ARs is associated with incident heart failure in patients with hypertension. Collectively, these findings suggest that alpha-1-AR activation might mitigate the well-recognized toxic effects of beta-ARs in the hyperadrenergic setting of chronic heart failure. Thus, exogenous cardioselective activation of alpha-1-ARs might represent a novel and viable approach to the treatment of heart failure.

Alpha1a-adrenoceptor genetic variant induces cardiomyoblast-to-fibroblast-like cell transition via distinct signaling pathways

The role of naturally occurring human α1a-Adrenergic Receptor (α1aAR) genetic variants associated with cardiovascular disorders is poorly understood. Here, we present the novel findings that expression of human α1aAR-247R (247R) genetic variant in cardiomyoblasts leads to transition of cardiomyoblasts into a fibroblast-like phenotype, evidenced by morphology and distinct de novo expression of characteristic genes. These fibroblast-like cells exhibit constitutive, high proliferative capacity and agonist-induced hypertrophy compared with cells prior to transition. We demonstrate that constitutive, synergistic activation of EGFR, Src and ERK kinases is the potential molecular mechanism of this transition. We also demonstrate that 247R triggers two distinct EGFR transactivation-dependent signaling pathways: 1) constitutive Gq-independent β-arrestin-1/Src/MMP/EGFR/ERK-dependent hyperproliferation and 2) agonist-induced Gq- and EGFR/STAT-dependent hypertrophy. Interestingly, in cardiomyoblasts agonist-independent hyperproliferation is MMP-dependent, but in fibroblast-like cells it is MMP-independent, suggesting that expression of α1aAR genetic variant in cardiomyocytes may trigger extracellular matrix remodeling. Thus, these novel findings demonstrate that EGFR transactivation by α1aAR-247R leads to hyperproliferation, hypertrophy and alterations in cardiomyoblasts, suggesting that these unique genetically-mediated alterations in signaling pathways and cellular function may lead to myocardial fibrosis. Such extracellular matrix remodeling may contribute to the genesis of arrhythmias in certain types of heart failure.

Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance

Adrenergic receptors (AR) are G-protein-coupled receptors (GPCRs) that have a crucial role in cardiac physiology in health and disease. Alpha1-ARs signal through Gαq, and signaling through Gq, for example, by endothelin and angiotensin receptors, is thought to be detrimental to the heart. In contrast, cardiac alpha1-ARs mediate important protective and adaptive functions in the heart, although alpha1-ARs are only a minor fraction of total cardiac ARs. Cardiac alpha1-ARs activate pleiotropic downstream signaling to prevent pathologic remodeling in heart failure. Mechanisms defined in animal and cell models include activation of adaptive hypertrophy, prevention of cardiac myocyte death, augmentation of contractility, and induction of ischemic preconditioning. Surprisingly, at the molecular level, alpha1-ARs localize to and signal at the nucleus in cardiac myocytes, and, unlike most GPCRs, activate "inside-out" signaling to cause cardioprotection. Contrary to past opinion, human cardiac alpha1-AR expression is similar to that in the mouse, where alpha1-AR effects are seen most convincingly in knockout models. Human clinical studies show that alpha1-blockade worsens heart failure in hypertension and does not improve outcomes in heart failure, implying a cardioprotective role for human alpha1-ARs. In summary, these findings identify novel functional and mechanistic aspects of cardiac alpha1-AR function and suggest that activation of cardiac alpha1-AR might be a viable therapeutic strategy in heart failure.

Relevance of the volume-axis intercept, V0, compared with the slope of end-systolic pressure-volume relationship in response to large variations in inotropy and afterload in rats

The end-systolic pressure-volume relationship (ESPVR) is proposed and used as a reliable index of left ventricular (LV) contractility despite the fact that its afterload independence has been challenged. Furthermore, the physiological relevance of its volume-axis intercept, V(0), remains unclear. Systemic haemodynamics and pressure-volume loops obtained by inferior vena cava occlusion were recorded in 21 rats anaesthetized by isoflurane inhalation and instrumented with a conductance pressure-volume catheter in response to incremental I.V. doses of adrenaline, dobutamine, phenylephrine, metoprolol, papaverine and isoflurane inhalation. In conditions with large variations (± 100%) of both inotropy and afterload, infusion of negative inotropic drugs was associated with a dose-dependent rightward shift of ESPVR accompanied by a decrease in its slope (end-systolic elastance, E(es)), whereas positive inotropic agents produced an isolated decrease in V(0). With the predominant vasoactive drugs, there was a dose-dependent change in E(es) without major horizontal shifts, demonstrating that this slope mainly represents LV afterload rather than inotropy. When contractility was altered, V(0) was negatively correlated to the preload-adjusted contractility index, PAdP/dt(max), demonstrating that a reduced V(0) provides a good reflection of increased LV contractility. From these results, we computed a logarithmically adjusted E(es)/V(0) ratio, which resulted in reasonably strong concordance with PAdP/dt(max), including all the investigated drugs and dosages [n = 288; bias, 0.8 ± 16.2% (SD)]. Concordance with E(es) (bias, 7.2 ± 58.7%) or V(0) (bias, -0.6 ± 33.4%), used alone or with other commonly used contractility indices, was far less significant. In contrast to E(es), V(0) provides a relatively good LV contractility index because it is much less sensitive to afterload.

The physiologic implications of isolated alpha(1) adrenergic stimulation

Phenylephrine and methoxamine are direct-acting, predominantly α(1) adrenergic receptor (AR) agonists. To better understand their physiologic effects, we screened 463 articles on the basis of PubMed searches of "methoxamine" and "phenylephrine" (limited to human, randomized studies published in English), as well as citations found therein. Relevant articles, as well as those discovered in the peer-review process, were incorporated into this review. Both methoxamine and phenylephrine increase cardiac afterload via several mechanisms, including increased vascular resistance, decreased vascular compliance, and disadvantageous alterations in the pressure waveforms produced by the pulsatile heart. Although pure α(1) agonists increase arterial blood pressure, neither animal nor human studies have ever shown pure α(1)-agonism to produce a favorable change in myocardial energetics because of the resultant increase in myocardial workload. Furthermore, the cost of increased blood pressure after pure α(1)-agonism is almost invariably decreased cardiac output, likely due to increases in venous resistance. The venous system contains α(1) ARs, and though stimulation of α(1) ARs decreases capacitance and may transiently increase venous return, this gain may be offset by changes in afterload, venous compliance, and venous resistance. Data on the effects of α(1) stimulation in the central nervous system show conflicting changes, while experimental animal data suggest that renal blood flow is reduced by α(1)-agonists, and both animal and human data suggest that gastrointestinal perfusion may be reduced by α(1) tone.

Cardiac and neuroprotection regulated by α(1)-adrenergic receptor subtypes

Sympathetic nervous system regulation by the α(1)-adrenergic receptor (AR) subtypes (α(1A), α(1B), α(1D)) is complex, whereby chronic activity can be either detrimental or protective for both heart and brain function. This review will summarize the evidence that this dual regulation can be mediated through the different α(1)-AR subtypes in the context of cardiac hypertrophy, heart failure, apoptosis, ischemic preconditioning, neurogenesis, locomotion, neurodegeneration, cognition, neuroplasticity, depression, anxiety, epilepsy, and mental illness.

Antiarrhythmic and antioxidant activity of novel pyrrolidin-2-one derivatives with adrenolytic properties

A series of novel pyrrolidin-2-one derivatives (17 compounds) with adrenolytic properties was evaluated for antiarrhythmic, electrocardiographic and antioxidant activity. Some of them displayed antiarrhythmic activity in barium chloride-induced arrhythmia and in the rat coronary artery ligation-reperfusion model, and slightly decreased the heart rate, prolonged P–Q, Q–T intervals and QRS complex. Among them, compound EP-40 (1-[2-hydroxy-3-[4-[(2-hydroxyphenyl)piperazin-1-yl]propyl]pyrrolidin-2-one showed excellent antiarrhythmic activity. This compound had significantly antioxidant effect, too. The present results suggest that the antiarrhythmic effect of compound EP-40 is related to their adrenolytic and antioxidant properties. A biological activity prediction using the PASS software shows that compound EP-35 and EP-40 can be characterized by antiischemic activity; whereas, compound EP-68, EP-70, EP-71 could be good tachycardia agents.

Increased diastolic time fraction as beneficial adjunct of α1-adrenergic receptor blockade after percutaneous coronary intervention

The effect of α1-receptor blockade with urapidil on coronary blood flow and left ventricular function has been attributed to relief of diffuse coronary vasoconstriction following percutaneous coronary intervention (PCI). We hypothesized that an increase in diastolic time fraction (DTF) contributes to the beneficial action of urapidil. In eleven patients with a 63% (SD 13) diameter stenosis, ECG, aortic pressure (Pa) and distal intracoronary pressure (Pd), and blood flow velocity were recorded at baseline and throughout adenosine-induced hyperemia. Measurements were obtained before and after PCI and after subsequent α1-receptor blockade with urapidil (10 mg ic). DTF was determined from the ECG and the Pa waveform. Functional parameters such as coronary flow velocity reserve, fractional flow reserve, and an index of hyperemic microvascular resistance (HMR) were assessed. Urapidil administration after PCI induced an upward shift in the DTF-heart rate relationship, resulting in a 3.1% (SD 2.7) increase in hyperemic DTF at a constant heart rate ( P < 0.005) due to a shorter duration of systole. Hyperemic Pa and Pd decreased, respectively, by 6.1% (SD 6.6; P < 0.05) and 5.7% (SD 5.8; P < 0.01) after α1-blockade. Although epicardially measured functional parameters were on average not altered by α1-blockade due to concurrent changes in pressure and heart rate, HMR decreased by urapidil in those patients where coronary pressure remained constant. In conclusion, α1-receptor blockade after PCI produced a modest but significant prolongation of DTF at a given heart rate, thereby providing an adjunctive beneficial mechanism for improving subendocardial perfusion, which critically depends on DTF.

Simultaneous blockade of alpha1- and beta-actions of epinephrine during cardiopulmonary resuscitation

OBJECTIVE

Experimental and clinical studies have implicated that alpha1- and beta-adrenergic effects of epinephrine significantly increased the severity of postresuscitation myocardial dysfunction by increasing myocardial oxygen consumption during ventricular fibrillation. This prompted experimental studies to investigate the effect of simultaneous blockade of alpha1- and beta-actions of epinephrine during cardiopulmonary resuscitation.

DESIGN

Literature review.

RESULTS

Improved postresuscitation myocardial dysfunction was observed in epinephrine-treated animals after its alpha1- and beta-actions were blocked, which were associated with less postresuscitation arrhythmia, lower blood lactate level, better neurologic recovery, and longer duration of survival.

CONCLUSIONS

After simultaneous alpha1- and beta-adrenergic blockade, epinephrine administered during cardiopulmonary resuscitation yielded improved postresuscitation myocardial functions and significantly better postresuscitation outcomes.

Vasopressors for cardiopulmonary resuscitation. Does pharmacological evidence support clinical practice?

Adrenaline (epinephrine) has been used for cardiopulmonary resuscitation (CPR) since 1896. The rationale behind its use is thought to be its alpha-adrenoceptor-mediated peripheral vasoconstriction, causing residual blood flow to be diverted to coronary and cerebral circulations. This protects these tissues from ischaemic damage and increases the likelihood of restoration of spontaneous circulation. Clinical trials have not demonstrated any benefit of adrenaline over placebo as an agent for resuscitation. Adrenaline has deleterious effects in the setting of resuscitation, predictable from its promiscuous pharmacological profile. This article discusses the relevant pharmacology of adrenaline in the context of CPR. Experimental and clinical evidences for the use of adrenaline and alternative vasopressor agents in resuscitation are given, and the properties of an ideal vasopressor are discussed.

Effects of hypertension on cardiovascular responses to epinephrine in humans

Cardiac beta-receptor responsiveness is diminished by both aging and hypertension. However, concomitant decreases in the activity of counterregulatory mechanisms, such as the arterial baroreflex and neuronal catecholamine uptake, influence the ultimate cardiac responses to adrenergic agents in vivo. In the present study, we evaluated by echocardiography cardiac responses to intravenous infusion of epinephrine in 14 young and 18 older normotensive men and women and in 10 young and 17 older hypertensive men and women. To assess the relative contribution of intrinsic cardiac and counterregulatory components to the overall response, infusions were repeated combined with a ganglionic blocker in the young groups. Epinephrine-induced increases in heart rate were similar in the four groups. Increases in stroke volume, ejection fraction, and cardiac index were similar in the two hypertensive and two young normotensive groups. In contrast, they were attenuated in the older normotensive group, resulting in higher left ventricular responses in older hypertensive than in normotensive subjects. Heart rate and left ventricular responses to epinephrine in the presence of ganglionic blockade did not differ between the two young groups. Increases in plasma norepinephrine due to epinephrine infusion were larger in hypertensive than in normotensive subjects. One may conclude that compared with young normotensive subjects, in hypertensive subjects mechanisms increasing versus decreasing cardiac responses to epinephrine may remain in balance, and, compared with older normotensive subjects, older hypertensive subjects exhibit enhanced cardiac responses to sympathetic stimulation.

[Utility of vasopressin in cardiopulmonary resuscitation]

Many vasopressants have been studied in cardiopulmonary resuscitation (CPR) to increase cerebral and coronary perfusion. Although there is a debate on the utility of epinephrine, this is the one that has been used historically, above all after verifying that other agents such as norepinephrine, metoxamine or phenylephrine, have not been shown to be more effective. Currently, due to the good experimental results, the use of vasopressin (ADH) in CPR is being evaluated. However there is little (only three studies) and debated evidence based on randomized clinical trials (norepinephrine or ADH) in humans. Once these are reviewed, it can be concluded: The results of the three randomized studies in humans obtain different results regarding the utility of ADH in cardiorespiratory arrest (CRA) secondary to ventricular fibrillation, electro-mechanical dissociation or asystole. More prospective studies are needed to know the role of ADH in prolonged CRA and in asystole, that may be the subgroups that can benefit the most from this drug. The neurological repercussion of a drug in the context of CRA should be evaluated before its inclusion in the CPR guides.

Epinephrine and vasopressin during cardiopulmonary resuscitation

Epinephrine (adrenaline) and vasopressin have been by far the most commonly studied vasopressors in experimental cardiac arrest. Despite animal experimental studies suggesting improved outcomes in experimental cardiac arrest, clinical trials of pressor agents have failed to show clear cut benefit from either vasopressin or epinephrine, although few, if any, trials compared pressor agents to a placebo. The action of vasopressors in the heart, particularly beta1-adrenergic stimulation, is associated with adverse cardiac effects including post-resuscitation myocardial dysfunction, worsening ventricular arrhythmias, and increasing myocardial oxygen consumption. Alpha2-adrenergic agonists, in experimental studies, show great promise in improving outcomes in experimental cardiac arrest, but have not been studied in humans. The combination of epinephrine and vasopressin may be effective, but has been incompletely studied. Clinical trials of vasopressor agents, which minimize direct myocardial effects are needed.

Canine idiopathic dilated cardiomyopathy. Part II: pathophysiology and therapy

Dilated cardiomyopathy (DCM) in dogs is characterized by ventricular and atrial enlargement, and systolic and diastolic dysfunction, with congestive heart failure (CHF) often developing at some stage. With greater understanding of the impact of neuroendocrine stimulation in heart disease, the understanding of the pathophysiology for CHF has changed considerably. It is no longer considered only to be a simple haemodynamic consequence of pump dysfunction, but is now characterized as a complex clinical syndrome with release of many neurohormones, which are believed to have impact on the progression of disease. This change in our understanding of the pathophysiology of CHF has important therapeutic implications. There are strong indications, although not yet proven, that drugs designed to influence the neuroendocrine activity, such as Angiotensin Converting Enzyme (ACE) inhibitors and beta-receptors antagonists, are efficacious as adjunct therapy of heart failure attributable to DCM in dogs. The benefits of drugs designed to influence the myocardial contractile state (positive inotropes) have not been fully evaluated. However, evidence has emerged in recent years indicating that new types of positive inotropes may be beneficial in dogs with DCM. This review focuses on the neuroendocrine aspects of DCM and their possible therapeutic implications and the place for long-term inotropic support in dogs with DCM.

Intracoronary-administered urapidil does not influence myocardial contractility, metabolic activity, or coronary sinus blood flow in humans

OBJECTIVE

To compare the acute effect of intracoronary administration of urapidil and saline on myocardial contractility and metabolic activity.

DESIGN

Prospective, controlled, open-label study.

SETTING

University teaching hospital.

PARTICIPANTS AND INTERVENTIONS

Eight patients with stable coronary artery disease (CAD) undergoing elective percutaneous transluminal coronary angioplasty (PTCA) received normal saline followed by urapidil, 4 mg, injected directly into the left main coronary artery.

MEASUREMENTS AND MAIN RESULTS

Because local intracoronary administration is a non-steady-state condition, an in vitro model was used before the clinical experiments to establish the kinetic effects of acute administration of urapidil. The clinical experiments were performed in eight patients with CAD after PTCA. Measurements included a complete hemodynamic profile, coronary sinus blood flow (continuous thermodilution), left ventricular (LV) peak (+) dP/dt, LV peak (-) dP/dt, LV dP/dt/P(D)40, and LV end-diastolic pressures. Arterial and coronary venous blood samples were also obtained for the calculation of myocardial oxygen consumption. Baseline measurements I were first obtained, followed by intracoronary injection of 2 mL of saline. Additional measurements were obtained 1, 5, and 10 minutes after administration of saline. After a resting period (15 minutes), baseline measurements II, and intracoronary injection of urapidil, 4 mg (dissolved in 2 mL saline), additional measurements were obtained 1, 5, and 10 minutes later. Heart rate decreased 2.7+/-3.5 beats/min after injection of saline, whereas heart rate increased 2.0+/-1.8 beats/min after intracoronary urapidil, resulting in a significant difference in treatment effect (p = 0.003). There were no additional differences in treatment effect for any of the other measured or calculated parameters reflecting systemic hemodynamics, LV contractility, coronary dynamics, and myocardial metabolic activity.

CONCLUSION

The results suggest that intracoronary bolus administration of preservative-free urapidil, 4 mg, is not associated with any detectable effect on myocardial contractility or coronary smooth muscle in awake nonsurgical patients with CAD, after PTCA.

Perioperative care in left ventricular volume reduction

BACKGROUND

While the operative technique of left ventricular volume reduction (LVVR) is rapidly becoming standardized, the optimal perioperative management strategy is yet to be determined. We present our experience with the care of patients undergoing LVVR.

METHODS

LVVR was performed in 21 patients (mean age = 65.5 years) with congestive heart failure. Our management strategy was initially based on afterload reduction with sodium nitroprusside, but was later modified to include routine preoperative intra-aortic balloon support, normothermic cardiopulmonary bypass, antegrade intermittent warm blood cardioplegia, and postoperative support with phosphodiesterase-III inhibitors. Hemodynamic manipulations are aimed to attain systemic vascular resistance between 600 and 800 dyne/sec per cm(-5) and the lowest mean blood pressure that is able to maintain satisfactory systemic perfusion. Postoperatively, aggressive antifailure medical therapy with a high dose of angiotensin converting enzyme inhibitors, nitrates, and diuretics was initiated early and maintained indefinitely.

RESULTS

Using this approach, postoperative progress was characterized by hemodynamic stability. IABP support was used for 59.6+/-9 hours following surgery, and inotropic support for 103+/-12 hours. In our series there were four (19%) in-hospital deaths, two of which were related to heart failure.

CONCLUSION

The described approach is associated with an acceptable early outcome. However, further advances in myocardial protection methods and pharmacological and mechanical support techniques are necessary for a wider adoption of this procedure.

In vivo demonstration of alpha-adrenoceptor-mediated positive inotropy in pithed rats: evidence that noradrenaline does not stimulate myocardial alpha-adrenoceptors

1. This study examines whether positive inotropy via alpha-adrenoceptors could be observed in vivo in pithed rats. Cardiac contractility was measured as the maximum rate of rise of left ventricular pressure (dP/dt(max)). Heart rate and aortic blood pressure were also recorded. 2. The selective alpha1-adrenoceptor agonists, methoxamine, cirazoline, amidephrine and phenylephrine caused dose-related increases in dP/dt(max). This response was progressively reduced by increasing doses of the alpha1-adrenoceptor antagonist prazosin. However, since the concomitant increase in diastolic blood pressure (DBP) was also blocked, the changes in dP/dt(max) may have been a consequence of increased after load. 3. Adrenaline and noradrenaline also increased dP/dt(max), accompanied by pressor responses. Propranolol (1 mg kg(-1)) antagonized the increase in dP/dt(max) in response to noradrenaline, suggesting beta-adrenoceptor involvement, but not that to adrenaline. The additional presence of prazosin (1 mg kg(-1)) further shifted the dose-response curves for both noradrenaline and adrenaline to the right. 4. Analysis of the increases in dP/dt(max) at predetermined increases in DBP by each agonist revealed three groups of regression lines. Adrenaline in the presence of propranolol and the four selective alpha1-adrenoceptor agonists occupied a common central position. Above this group were adrenaline and noradrenaline in the absence of antagonists; their additional effects on contractility were beta-adrenoceptor-mediated since the regression lines were lowered by propranolol. Clearly below the main group of agonists was noradrenaline in the presence of propranolol. 5. Thus, for a given increase in DBP, adrenaline (in the presence of beta-blockade) and the alpha1-adrenoceptor agonists exert an additional inotropic effect to noradrenaline (also in the presence of beta-blockade). This is concluded to be an alpha-adrenoceptor-mediated increase in cardiac contractility which is not shared by noradrenaline.

Overexpression of alpha1B-adrenergic receptor induces left ventricular dysfunction in the absence of hypertrophy

The stimulation of cardiac alpha1-adrenergic receptors (AR) modulates the heart's inotropic response and plays a role in the induction of cardiomyocyte hypertrophy. We have analyzed transgenic mouse lines overexpressing a wild-type alpha1B-AR specifically in the heart. Basal level systolic and diastolic left ventricular (LV) contractile function was depressed both in the anesthetized closed-chest mouse and the perfused working-heart preparation. Intrinsic LV function was further characterized under controlled preload and afterload conditions using the perfusion model. Contractile parameters were restored by chronic treatment with the alpha-AR antagonist prazosin. In ventricular function curves, the load-dependent force increases (length-tension effects) remained intact, although the transgenic curve was shifted to lower levels. The basal level contractile deficits were paralleled by a decrease in calcium transients in isolated LV cardiomyocytes. LV function comparable to controls was restored by isoproterenol stimulation. The physiological changes occurred in the absence of cardiomyocyte hypertrophy. This transgenic model will be useful for studying the potential role of alpha1-AR in cardiac contractility and hypertrophy.

Mechanism of action of beta-blocking agents in heart failure

Antiadrenergic treatment is currently an emerging and very promising approach to the treatment of chronic heart failure. Although the adrenergic nervous system can be pharmacologically inhibited at multiple levels, it is the use of receptor-blocking agents that has generated the most interest and provided the most data for the "proof of concept" of this approach. In part because antiadrenergic treatment of chronic heart failure has developed in an atmosphere in which it was initially considered to be contraindicated (i.e., before Phase III clinical trials could be initiated), a large body of hypothesis-driven basic and clinical investigation was required to define the overall rationale and demonstrate feasibility. This article will review these data and propose a single primary mechanism of action to explain most of the clinical benefits of these agents.

Ventriculoarterial coupling and left ventricular efficiency in heart transplant recipients

BACKGROUND

In heart transplants, left ventricular function may be impaired in the absence of rejection or graft atherosclerosis. Matching between left ventricle and arterial receptor, i.e., ventriculoarterial coupling, and left ventricular efficiency have never been studied.

METHODS

Left ventricular pressure-volume loops and single beat analysis were used to determine effective arterial elastance (Ea) and the slope of the end-systolic pressure-volume relation (end-systolic elastance; Ees). Left ventricular efficiency was evaluated by determination of external work (EW), pressure-volume area (PVA), coronary blood flow (continuous thermodilution), and myocardial oxygen consumption (MVO2). Measurements were made at baseline in 11 control subjects and 9 heart transplant recipients (HTX) without rejection and were repeated after phenylephrine in the latter group.

RESULTS

At baseline, Ees, Ees/Ea, and work efficiency (EW/PVA) were lower in HTX than in control subjects (2.51+/-0.87 vs. 3.70+/-1.15 mmHg/ml/m2, P<0.01; 0.96+/-0.21 vs. 1.47+/-0.31, P<0.001; and 0.53+/-0.08 vs. 0.59+/-0.09, P<0.01, respectively). Energy conversion efficiency (PVA/MVO2) and mechanical efficiency (EW/ MVO2) were higher in HTX (0.58+/-0.08 vs. 0.45+/-0.14, P<0.001; and 0.31+/-0.05 vs. 0.26+/-0.06, P<0.001, respectively). In HTX, phenylephrine infusion increased Ees, Ea, EW, PVA, and MVO2 without modifying Ees/Ea, EW/PVA, PVA/MVO2, and EW/MVO2.

CONCLUSIONS

In heart transplants, (1) left ventricular contractility is moderately depressed; (2) elevation of energy conversion efficiency compensates for the decrease in work efficiency, allowing normal mechanical efficiency; and (3) alpha 1 adrenergic stimulation does not impair ventriculoarterial coupling and mechanical efficiency.

Myocardial alpha1-adrenoceptor: inotropic effect and physiologic and pathologic implications

Alpha1-adrenergic receptors have been found in myocardium of all mammalian species. Although the exact underlying mechanisms have not been conclusively determined, it would appear that the myocardial effects of alpha1-adrenoceptors may vary in importance according to the pathophysiologic process involved. In physiological conditions, this receptor system plays a role in cardiac growth, cardiac contraction, and has both an antiarrhythmic function as well as a role in cardiac adaptation to various situations. This system is also involved in some pathological processes such as ischemia/reperfusion, ischemic preconditioning, and cardiac hypertrophy. The role of alpha1-adrenoceptors in heart failure is somewhat controversial. Experimental evidence suggests that myocardial alpha1-adrenoceptors can have either beneficial or deleterious effects on the heart. It thus seems possible that the development of agents specific to certain subtypes of alpha1-adrenoceptor and a better understanding of their role in pathophysiologic states could be clinically relevant.

Localization of alpha 1-adrenoceptors in rat and human hearts by immunocytochemistry

The localization of the alpha 1 adrenoceptors (alpha 1-AR) in the heart tissues from rat and human and in the cultured heart cells from neonatal rats was studied by indirect immunofluorescence and postembedding electronmicroscopical immuno-gold technique. With antipeptide antibodies directed against the second extracellular loop of the human alpha 1-AR (AS sequence 192-218), this receptor was found to be localized along the sarcolemma in both human and rat hearts. Similar localization sites were detected in cultivated rat neonatal cardiomyocytes. Beside the localization in cardiomyocytes, alpha 1-AR were identified in endothelial cells of capillaries and smooth muscle cells of coronary vessels, in neuronal endings, in mast cells of cultivated heart cells but not, or in less amount in fibroblasts. Interestingly, in the right atrium of rat heart the localization of alpha 1-AR was found to be near or on atrial natriuretic factor (ANF) granules, providing the basis for the alpha-adrenergic influence on ANF release. The immunocytochemical studies further confirm and complete the findings known by using autoradiographic binding studies with specific ligands.

alpha 1-Adrenoceptor stimulation inhibits the isoproterenol-induced effects on myocardial contractility and protein phosphorylation

In the present study the influence of alpha 1-adrenoceptor stimulation on the beta-adrenoceptor agonist-induced increases in contractile parameters and protein phosphorylation was determined in isolated perfused hearts and isolated cardiac myocytes, respectively. Methoxamine inhibited the isoproterenol-induced increases in left ventricular pressure and heart rate dose dependently up to 90% and 75%, respectively; the EC50 of this antiadrenergic effect was 4.4 microM. The alpha 1-adrenoceptor antagonist, prazosin (1 microM), greatly diminished methoxamine's inhibitory action, confirming the alpha 1-adrenoceptor-mediated mechanism. The inotropic effect of glucagon was inhibited by methoxamine in a similar manner. Radioligand binding assays with [3H]dihydroalprenolol demonstrated that the antiadrenergic action of methoxamine is not due to an unspecific beta-adrenoceptor blocking property. In an additional experimental series the effects of methoxamine and isoproterenol on the protein phosphorylation pattern of isolated cardiac myocytes were investigated. Isoproterenol increased the phosphorylation state of five proteins (6-kDa, phospholamban; 15-kDa; 28-kDa, troponin I; 97-kDa; 140-kDa) while in the experiments with methoxamine the 15-kDa protein was the only phosphorylated substrate. In the presence of methoxamine the isoproterenol-induced phosphorylation of phospholamban, troponin I and the 97-kDa and 140-kDa protein was markedly inhibited while the phosphorylation state of the 15-kDa protein remained unaltered. The present study clearly demonstrated that alpha 1-adrenoceptor stimulation potently inhibits the beta-adrenoceptor-mediated changes in contractile force and phosphorylation of key regulatory proteins, most likely through modulation of cAMP metabolism.

Orthodeoxia-platypnea due to intracardiac shunting--relief with transcatheter double umbrella closure

The safety and efficacy of transcatheter clamshell occlusion of patent foramen ovale for relief of severe arterial desaturation and dyspnea in the upright position due to intracardiac shunting were examined in eight patients with excessive risk of surgical patent foramen ovale closure. All patients had successful reduction of intracardiac shunting with an immediate rise in oxygen saturation > or = 95% by implantation of a clamshell device on the atrial septum. Despite two early incidents of device embolization, retrieval and immediate re-implantation, and one patient with nonsustained atrial and ventricular arrhythmias, there were no adverse clinical sequelae. In follow-up evaluation transcatheter clamshell closure of patent foramen ovale has provided persistent relief from shunt-related arterial desaturation and symptomatology in all living patients.

New directions in the treatment of heart failure: some paradoxical observations

The alpha-agonist drug phenylephrine has been generally considered to be contraindicated in patients with heart failure for the reason that increased afterload produced by the vasoconstriction should decrease ventricular function; the beta-adrenergic blocking drugs generally have been considered to be contraindicated in heart failure because of the dependence of the failing heart on beta-sympathetic agonism; the angiotensin converting enzyme inhibitors have been indicted recently as causing undesirable cardiovascular depression in patients for coronary artery bypass surgery. Yet recently, phenylephrine has been shown to have positive cardiac inotropic effects in a variety of experimental preparations including intact humans; the beta-adrenergic blocking drugs have been shown to be therapeutically effective in treating patients with chronic congestive heart failure (CHF); and the "gold standard" for treating chronic CHF at present are the ACEI. Consequently, the clinician caring for patients with cardiac disease needs to reevaluate the use of classic drugs whose original pharmacological properties may either have changed because of advances in technology or may be producing effects that were unanticipated previously.

Myocardial alpha 1A-adrenoceptor subtypes in rabbit: differentiation by a selective antagonist, HV723

The influence of a newly developed alpha 1-adrenoceptor antagonist, HV723 (alpha-ethyl-3,4,5-trimethoxy-alpha-(3-((2-(2-methoxy-phenoxy)ethyl)-ami no)- propyl) benzeneacetonitrile fumarate), on the positive inotropic effect and acceleration of phosphoinositide hydrolysis induced by phenylephrine via alpha 1-adrenoceptors in the presence of bupranolol (0.3 microM) was studied in the rabbit ventricular muscle: (1) HV723 at low concentrations (1-100 pM) attenuated the maximal inotropic response by 15-20% without altering the pD2 value for and [3H]inositol monophosphate accumulation induced by phenylephrine. The inhibitory action of HV723 (1-100 pM) showed a close resemblance to that of a selective alpha 1A antagonist, (+)-niguldipine. (2) HV723 (> or = 1 nM) shifted the concentration-response curve for phenylephrine to the right and downwards in association with a partial inhibition (42.5%) of [3H]inositol monophosphate accumulation. The IC50 values of HV723 for the inhibition of the inotropic response and phosphoinositide hydrolysis were approximately equal to the Kilow value determined by displacement of [3H]prazosin-specific binding. The mode of the inhibitory action of HV723 (> or = 1 nM) resembled that of another alpha 1A antagonist, WB 4101. These results indicate that HV723 shows a differential antagonistic action on the alpha 1A-mediated responses depending on the concentration: HV723 (1-100 pM) selectively inhibits the (+)-niguldipine-sensitive subclass to lead to a decrease in the maximal inotropic response with no change in phosphoinositide hydrolysis; HV723 (> or = 1 nM) may antagonize the WB 4101-sensitive subtype coupled to acceleration of phosphoinositide hydrolysis.

Changes in myocardial and vascular receptors in heart failure

Heart failure results in dramatic changes in certain neurotransmitter and hormone receptors. The majority of the changes occur in the heart and generally can be classified as regulatory phenomena that withdraw the failing heart from adrenergic stimulation. Of these, the most prominent is beta 1-receptor downregulation. Changes in vascular receptors are much less prominent and there is no direct evidence that any vascular receptor changes in heart failure. The changes that occur in myocardial receptors suggest that antiadrenergic therapy would be effective in the treatment of heart failure by removing adrenergic signaling transduced by the remaining components of the receptor pathways. Taken together, the receptor desensitization changes present in the failing heart provide a rationale for beta 1- plus beta 2-adrenergic blockade or even combined beta 1-, beta 2-alpha 1-adrenergic receptor blockade in heart failure.