Exercise Preconditioning Preserves Cardiac Function and Enhances Cardiac Recovery Following Dobutamine Stimulation in Doxorubicin-Treated Rat Hearts.

ABSTRACT: Exercise preconditioning has been shown to protect against doxorubicin (DOX)-induced cardiac dysfunction when hearts are maintained under resting conditions. However, it is unclear whether this exercise-induced protective effect is maintained when the heart is challenged with the ß 1 -adrenergic receptor agonist dobutamine (DOB), which mimics acute exercise stress. Fischer 344 rats were randomly assigned to sedentary (SED) or voluntary wheel running (WR) groups for 10 weeks. At week 11, rats were treated with either 15 mg/kg DOX or saline. Five days later, ex vivo cardiac function was assessed using an isolated working heart model at baseline, during the infusion of 7.5 µg·kg -1 ·min -1 DOB, and during recovery. DOB infusion significantly increased left ventricular developed pressure (LVDP), maximal (dP/dt max ) and minimal (dP/dt min ) rate of left ventricular pressure development, and heart rate in all groups ( P < 0.05). SED + DOX also showed a lower baseline and recovery LVDP than WR + DOX (83 ± 12 vs. 109 ± 6 mm Hg baseline, 76 ± 11 vs. 100 ± 10 mm Hg recovery, P < 0.05). WR + DOX showed higher dP/dt max and lower dP/dt min when compared with SED + DOX during DOB infusion (7311 ± 1481 vs. 5167 ± 1436 mm Hg/s and -4059 ± 1114 vs.-3158 ± 1176 mm Hg/s, respectively). SED + DOX dP/dt max was significantly lower during baseline and during recovery when compared with all other groups ( P < 0.05). These data suggest that exercise preconditioning preserved cardiac function after DOX exposure even when the heart is challenged with DOB, and it appeared to preserve the heart's ability to recover from this functional challenge.

Relationship of Inotropic Effects of Stimulation of ß1- and ß2-Adrenergic Receptors of Isolated Myocardial Fragments with Echocardiography Parameters in Coronary Heart Disease.

We studied the relationship of inotropic responses of the isolated myocardium to stimulation of ß1-and ß2-adrenergic receptors (ß-AR) with echocardiography parameters in 28 patients with coronary heart disease (CHD). Myocardial fragments (trabeculae of the right atrial appendage) were obtained during coronary artery bypass surgery. The inotropic response of the trabeculae was assessed in an isometric mode. Stimulation of ß1-and ß2-AR with agonists was performed against the background of preliminary α-AR blockade. In case of preserved ejection fraction, significant inotropic response of the trabeculae (135 (112; 154)% from the initial contraction amplitude) was observed after ß1-AR stimulation, while in reduced ejection fraction, its significant increase was observed after ß1-AR stimulation (126 (112; 170)% from the initial contraction amplitude). In patients with preserved and reduced ejection fraction, the correlations between the inotropic responses of the trabeculae to ß1-and ß2-AR stimulation and echocardiography parameters were different. The revealed differences reflect the degree of cardiac remodeling under condition of the studied pathology.

Physical and physiological effects of dobutamine stress echocardiography in low-gradient aortic stenosis.

Dobutamine stress echocardiography (DSE) is a useful tool for assessing low-gradient significant aortic stenosis (AS) and contractile reserve (CR), but its prognostic utility has become controversial in recent studies. We evaluated the impact of DSE on aortic valve physiological, structural, and left ventricular parameters in low-gradient AS. Consecutive patients undergoing DSE for low-gradient AS evaluation from September 2010 to July 2016 were retrospectively studied, and DSE findings were divided into four groups: with and without severe AS and/or CR. Relationships between left ventricular chamber quantification, CR, aortic valve Doppler during DSE, and calcium score [by computerized tomography (CT)] were analyzed. There were 258 DSE studies performed on 243 patients, mean age 77.6 ± 10.8 yr and 183 (70.1%) were males. With increasing dobutamine dose, apart from systolic blood pressure, left ventricular ejection fraction, flow, cardiac power output, and longitudinal strain magnitude, along with aortic valve area and mean aortic gradient were all significantly increased (P < 0.05). Flow and mean gradient increased in both the presence and absence of CR, whereas stroke volume and aortic valve area increased mainly in those with CR only. The aortic valve area increased in both patients with low and high calcium scores; however, the baseline area was lower in those with a higher calcium score. During DSE, aortic valve area increases with increase in aortic valve gradient. Higher calcium score is associated with lower baseline aortic valve area, but the aortic valve area still increases with dobutamine even in presence of a high calcium score.NEW & NOTEWORTHY We show that even in most severe aortic stenosis, there is some residual valve pliability. This suggests that a complete loss of pliability is not compatible with survival.

Backbone NMR reveals allosteric signal transduction networks in the ß1-adrenergic receptor.

G protein-coupled receptors (GPCRs) are physiologically important transmembrane signalling proteins that trigger intracellular responses upon binding of extracellular ligands. Despite recent breakthroughs in GPCR crystallography, the details of ligand-induced signal transduction are not well understood owing to missing dynamical information. In principle, such information can be provided by NMR, but so far only limited data of functional relevance on few side-chain sites of eukaryotic GPCRs have been obtained. Here we show that receptor motions can be followed at virtually any backbone site in a thermostabilized mutant of the turkey ß1-adrenergic receptor (ß1AR). Labelling with [(15)N]valine in a eukaryotic expression system provides over twenty resolved resonances that report on structure and dynamics in six ligand complexes and the apo form. The response to the various ligands is heterogeneous in the vicinity of the binding pocket, but gets transformed into a homogeneous readout at the intracellular side of helix 5 (TM5), which correlates linearly with ligand efficacy for the G protein pathway. The effect of several pertinent, thermostabilizing point mutations was assessed by reverting them to the native sequence. Whereas the response to ligands remains largely unchanged, binding of the G protein mimetic nanobody NB80 and G protein activation are only observed when two conserved tyrosines (Y227 and Y343) are restored. Binding of NB80 leads to very strong spectral changes throughout the receptor, including the extracellular ligand entrance pocket. This indicates that even the fully thermostabilized receptor undergoes activating motions in TM5, but that the fully active state is only reached in presence of Y227 and Y343 by stabilization with a G protein-like partner. The combined analysis of chemical shift changes from the point mutations and ligand responses identifies crucial connections in the allosteric activation pathway, and presents a general experimental method to delineate signal transmission networks at high resolution in GPCRs.

Metoprolol Impairs ß1-Adrenergic Receptor-Mediated Vasodilation in Rat Cerebral Arteries: Implications for ß-Blocker Therapy.

The practice of prescribing ß-blockers to lower blood pressure and mitigate perioperative cardiovascular events has been questioned because of reports of an increased risk of stroke. The benefit of ß-blocker therapy primarily relies on preventing activation of cardiac ß1-adrenergic receptors (ARs). However, we reported that ß1ARs also mediate vasodilator responses of rat cerebral arteries (CAs), implying that ß-blockers may impair cerebral blood flow under some conditions. Here, we defined the impact of metoprolol (MET), a widely prescribed ß1AR-selective antagonist, on adrenergic-elicited diameter responses of rat CAs ex vivo and in vivo. MET (1-10 µmol/l) prevented ß1AR-mediated increases in diameter elicited by dobutamine in cannulated rat CAs. The ß1AR-mediated dilation elicited by the endogenous adrenergic agonist norepinephrine (NE) was reversed to a sustained constriction by MET. Acute oral administration of MET (30 mg/kg) to rats in doses that attenuated resting heart rate and dobutamine-induced tachycardia also blunted ß1AR-mediated dilation of CAs. In the same animals, NE-induced dilation of CAs was reversed to sustained constriction. Administration of MET for 2 weeks in drinking water (2 mg/ml) or subcutaneously (15 mg/kg per day) also resulted in NE-induced constriction of CAs in vivo. Thus, doses of MET that protect the heart from adrenergic stimulation also prevent ß1AR-mediated dilation of CAs and favor anomalous adrenergic constriction. Our findings raise the possibility that the increased risk of ischemic stroke in patients on ß-blockers relates in part to adrenergic dysregulation of cerebrovascular tone. SIGNIFICANCE STATEMENT: ß-Blocker therapy using second-generation, cardioselective ß-blockers is associated with an increased risk of stroke, but the responsible mechanisms are unclear. Here, we report that either acute or chronic systemic administration of a cardioselective ß-blocker, metoprolol, mitigates adrenergic stimulation of the heart as an intended beneficial action. However, metoprolol concomitantly eliminates vasodilator responses to adrenergic stimuli of rat cerebral arteries in vivo as a potential cause of dysregulated cerebral blood flow predisposing to ischemic stroke.

Suppression of beta 2 adrenergic receptor actions prevent UVB mediated cutaneous squamous cell tumorigenesis through inhibition of VEGF-A induced angiogenesis.

Although beta 2 adrenergic receptors (ß2 ADR) are present in the keratinocytes, their role in cutaneous squamous cell tumorigenesis needs to be ascertained. For the first time, we report here that selective ß2 ADR antagonists by inhibiting ß2 ADR actions significantly retarded the progression of ultraviolet B (UVB) induced premalignant cutaneous squamous cell lesions. These antagonists acted by inhibiting vascular endothelial growth factor-A (VEGF) mediated angiogenesis to prevent UVB radiation-induced squamous cell carcinoma of the skin.

Calcium and Heart Failure: How Did We Get Here and Where Are We Going?

The occurrence and prevalence of heart failure remain high in the United States as well as globally. One person dies every 30 s from heart disease. Recognizing the importance of heart failure, clinicians and scientists have sought better therapeutic strategies and even cures for end-stage heart failure. This exploration has resulted in many failed clinical trials testing novel classes of pharmaceutical drugs and even gene therapy. As a result, along the way, there have been paradigm shifts toward and away from differing therapeutic approaches. The continued prevalence of death from heart failure, however, clearly demonstrates that the heart is not simply a pump and instead forces us to consider the complexity of simplicity in the pathophysiology of heart failure and reinforces the need to discover new therapeutic approaches.

Role of ß3-Adrenoceptor Activation in Changes of Pulmonary Microhemodynamics after Experimental Pulmonary Thromboembolism.

Changes in pulmonary microhemodynamics during modelling of pulmonary thromboembolism against the background of nebivolol and mirabegron pretreatment were studied in isolated perfused rabbit lungs. In both cases, the pulmonary artery pressure and precapillary and pulmonary vascular resistance increased to a greater extent than in control animals, but the increase in capillary hydrostatic pressure was less pronounced. The postcapillary resistance did not change in pulmonary embolism against the background of nebivolol administration and increased in case of mirabegron pretreatment; capillary filtration coefficient after nebivolol pretreatment increased less markedly than after mirabegron administration. The increase in capillary filtration coefficient after activation of ß3-adrenoceptors with the specified drugs depended on the ratio of constriction of pulmonary veins, capillary hydrostatic pressure, and endothelial permeability.

Embryonic developmental oxygen preconditions cardiovascular functional response to acute hypoxic exposure and maximal ß-adrenergic stimulation of anesthetized juvenile American alligators (Alligator mississippiensis).

The effects of the embryonic environment on juvenile phenotypes are widely recognized. We investigated the effect of embryonic hypoxia on the cardiovascular phenotype of 4-year-old American alligators (Alligator mississippiensis). We hypothesized that embryonic 10% O2 preconditions cardiac function, decreasing the reduction in cardiac contractility associated with acute 5% O2 exposure in juvenile alligators. Our findings indicate that dobutamine injections caused a 90% increase in systolic pressure in juveniles that were incubated in 21% and 10% O2, with the 10% O2 group responding with a greater rate of ventricular relaxation and greater left ventricle output compared with the 21% O2 group. Further, our findings indicate that juvenile alligators that experienced embryonic hypoxia have a faster rate of ventricular relaxation, greater left ventricle stroke volume and greater cardiac power following ß-adrenergic stimulation, compared with juvenile alligators that did not experience embryonic hypoxia. When juveniles were exposed to 5% O2 for 20 min, normoxic-incubated juveniles had a 50% decline in left ventricle maximal rate of pressure development and maximal pressure; however, these parameters were unaffected and decreased less in the hypoxic-incubated juveniles. These data indicate that embryonic hypoxia in crocodilians alters the cardiovascular phenotype, changing the juvenile response to acute hypoxia and ß-adrenergic stimulation.

Dobutamine Versus Vasopressin After Mesenteric Ischemia.

BACKGROUND: Gastrointestinal blood flow may be compromised during and after vasopressor support. Endothelin expression may lead to microcirculatory dysfunction. The aim of this study was to analyze the effect of vasopressin and dobutamine after mesenteric ischemia on the gastrointestinal mucosal microcirculation, endothelin expression, and morphologic injury. MATERIALS AND METHODS: Pigs were studied in four groups (six pigs in each group): 1, sham; 2-4 ischemia (1 h superior mesenteric artery occlusion with 30 min reperfusion and 30 min of vehicle [2], dobutamine [3], or vasopressin [4] administration, followed by 30-min break and thiopental-induced hypotension [3, 4]). Blood flow of the gastric, jejunal, and rectosigmoidal mucosa was measured. At the end of the experiment, the mucosal expression of endothelin-1 (ET-1) and its receptor subtypes A (ETA) and B were determined by polymerase chain reaction. Mucosal injury, apoptotic cell death, and leukocytic infiltration were determined by histology and immunohistochemical analysis of cleaved caspase-3 and myeloperoxidase. RESULTS: Mesenteric ischemia increased jejunal mucosal ET-1 gene expression, arterial ET-1, intestinal fatty acid binding protein, and jejunal mucosal injury compared with sham. Dobutamine increased arteriovenous shunting at the cost of the jejunal mucosal blood perfusion. This was associated with an increased expression of ET-1 and ETA and mucosal leukocytic infiltration. In contrast, vasopressin increased postischemic capillary density and tissue blood flow. This was associated with a lower ET-1 gene expression. Vasopressin did not induce jejunal mucosal leukocytic infiltration. CONCLUSIONS: Vasopressin reduces mesenteric ischemia-associated alterations of the microcirculation and tissue integrity, whereas dobutamine does not.

Higenamine, a Dual Agonist for ß 1- and ß 2-Adrenergic Receptors Identified by Screening a Traditional Chinese Medicine Library.

Chronic heart failure is the terminal stage of various cardiovascular diseases. Despite the availability of several classes of drugs, there is still an unmet need for effective treatment. Based on bench work during the past two decades, we have proposed that enhancement of ß 2-adrenergic receptor signaling in combination with the presently preferred ß 1-adrenergic receptor blockade would be a promising strategy. Chinese herbal medicines have been shown to be effective in the treatment of heart failure, although the mechanisms largely remain unknown. In the present study, we screened an herbal medicine compound/extract library for ß-adrenergic receptor ligands to determine the target of certain effective botanical remedies and seek a leading compound(s) for chronic heart failure treatment. Using a high-throughput screening assay, we identified higenamine, which has a long history in chronic heart failure treatment in traditional Chinese medicine, to be a potent ß-adrenergic receptor agonist. Further experiments using specific inhibitors showed that higenamine activated both ß 1-adrenergic receptor and ß 2-adrenergic receptor. Inhibition of its action by pertussis toxin (a Gi inhibitor) indicated that it is a ß 2-adrenergic receptor Gs/Gi dual agonist. Contractility experiments demonstrated a positive inotropic effect of higenamine. In conclusion, we found an herbal compound, higenamine, to be a dual agonist for ß 1/ß 2-adrenergic receptors with no preference in stimulating the Gs and Gi pathways in ß 2-adrenergic receptor signaling. Our results elucidated not only the target of higenamine to explain its pharmacological effect in treating chronic heart failure, but also the mechanisms of its cardiac toxicity.

Novel Paradigms Governing ß1-Adrenergic Receptor Trafficking in Primary Adult Rat Cardiac Myocytes.

The ß1-adrenergic receptor (ß1-AR) is a major cardiac G protein-coupled receptor, which mediates cardiac actions of catecholamines and is involved in genesis and treatment of numerous cardiovascular disorders. In mammalian cells, catecholamines induce the internalization of the ß1-AR into endosomes and their removal promotes the recycling of the endosomal ß1-AR back to the plasma membrane; however, whether these redistributive processes occur in terminally differentiated cells is unknown. Compartmentalization of the ß1-AR in response to ß-agonists and antagonists was determined by confocal microscopy in primary adult rat ventricular myocytes (ARVMs), which are terminally differentiated myocytes with unique structures such as transverse tubules (T-tubules) and contractile sarcomeres. In unstimulated ARVMs, the fluorescently labeled ß1-AR was expressed on the external membrane (the sarcolemma) of cardiomyocytes. Exposing ARVMs to isoproterenol redistributed surface ß1-ARs into small (∼225-250 nm) regularly spaced internal punctate structures that overlapped with puncta stained by Di-8 ANEPPS, a membrane-impermeant T-tubule-specific dye. Replacing the ß-agonist with the ß-blocker alprenolol, induced the translocation of the wild-type ß1-AR from these punctate structures back to the plasma membrane. This step was dependent on two barcodes, namely, the type-1 PDZ binding motif and serine at position 312 of the ß1-AR, which is phosphorylated by a pool of cAMP-dependent protein kinases anchored at the type-1 PDZ of the ß1-AR. These data show that redistribution of the ß1-AR in ARVMs from internal structures back to the plasma membrane was mediated by a novel sorting mechanism, which might explain unique aspects of cardiac ß1-AR signaling under normal or pathologic conditions.

Local metabolic hypothesis is not sufficient to explain coronary autoregulatory behavior.

The local metabolic hypothesis proposes that myocardial oxygen tension determines the degree of autoregulation by increasing the production of vasodilator metabolites as perfusion pressure is reduced. Thus, normal physiologic levels of coronary venous PO2, an index of myocardial oxygenation, are proposed to be required for effective autoregulation. The present study challenged this hypothesis through determination of coronary responses to changes in coronary perfusion pressure (CPP 140-40 mmHg) in open-chest swine in the absence (n = 7) and presence of euvolemic hemodilution (~ 50% reduction in hematocrit), with (n = 5) and without (n = 6) infusion of dobutamine to augment MVO2. Coronary venous PO2 decreased over similar ranges (~ 28-15 mmHg) as CPP was lowered from 140 to 40 mmHg in each of the groups. However, coronary venous PO2 was not associated with changes in coronary blood flow (r = - 0.11; P = 0.29) or autoregulatory gain (r = - 0.29; P = 0.12). Coronary zero-flow pressure (Pzf) was measured in 20 mmHg increments and determined to be directly related to vascular resistance (r = 0.71; P < 0.001). Further analysis demonstrated that changes in coronary blood flow remained minimal at Pzf > 20 mmHg, but progressively increased as Pzf decreased below this threshold value (r = 0.68; P < 0.001). Coronary Pzf was also positively correlated with autoregulatory gain (r = 0.43; P = 0.001). These findings support that coronary autoregulatory behavior is predominantly dependent on an adequate degree of underlying vasomotor tone, independent of normal myocardial oxygen tension.

In vitro evaluation of nebivolol effects on nonadrenergic noncholinergic responses in rabbit corpus cavernosum.

The purpose of this study was to compare the effects of nebivolol on nonadrenergic noncholinergic (NANC) relaxation functions that are mediated by electric field stimulation (EFS) in rabbit corpus cavernosum smooth muscle by comparison with other beta-adrenergic receptor blockers and show the level on which its effects through nitric oxide take place. After the effects of nebivolol on the isolated corpus cavernosum tissues that were contracted through the alpha-adrenergic pathway and application of L-NAME' (NG -nitro-L-arginine methyl ester) which is a competitive inhibitor of nitric oxide synthase (NOS), the changes that occurred were recorded. Following the effect on the tissue that was contracted with phenylephrine in the presence of atropine and guanethidine that was created by EFS, nebivolol and other beta-blockers were added and the changes were recorded. After receiving relaxation responses with EFS-mediated NANC, no difference was observed between the relaxation responses due to addition of nebivolol and other beta-adrenergic blockers (p > 0.05). The finding that nebivolol which has a NO-mediated relaxation effect did not have an effect on EFS-mediated NANC relaxation but created relaxation on the tissue that was contracted by phenylephrine and the effect was reversed by L-NAME, shows that its effects are on a postsynaptic level.

Protective effect of nebivolol on gentamicin-induced nephrotoxicity in rats.

OBJECTIVE: Nephrotoxicity is a major complication of gentamicin (GEN), which is widely used in the treatment of severe Gram-negative infections. As we know, treatment with nebivolol has been shown to decrease renal fibrosis and glomerular injury as well as improve endothelial dysfunction. Therefore, we evaluated the potential protective effect of nebivolol (NBV) against GEN-induced nephrotoxicity in rats. MATERIAL AND METHOD: Twenty-four rats were randomly divided into four groups: control group (Group 1); rats intraperitoneally injected with GEN (100 mg/kg/day; Group 2); rats treated with GEN plus distilled water (Group 3); and rats treated with GEN plus NBV (10 mg/kg/day; Group 4). After 15 days, the rats were sacrificed, their kidneys taken, and blood analysis performed. Tubular necrosis and interstitial fibrosis scores were determined histopathologically in a part of kidneys; nitric oxide (NO), malondialdehyde (MDA), and reduced glutathione (GSH) levels were determined in other part of kidneys. RESULTS: The GSH levels in renal tissue of only GEN-treated rats were significantly lower than those in control group, and administration of NBV to GEN-treated rats significantly increased the level of GSH. The group that was given GEN and NBV had significantly lower MDA and NO levels in kidney cortex tissue than that given GEN alone. Despite the presence of mild tubular degeneration, the rats treated with GEN+NBV showed a less severe tubular necrosis, and their glomeruli maintained a better morphology compared to GEN group. CONCLUSION: NBV exerts antioxidant, anti-inflammatory and antifibrotic effects on GEN-induced kidney damage by reducing oxidative stress in rat model (Tab. 3, Fig. 2, Ref. 68).

Antiadrenergic autoimmunity in postural tachycardia syndrome.

AIMS: Postural tachycardia syndrome (POTS), a common and debilitating cardiovascular disorder, is characterized by an exaggerated heart rate increase during orthostasis and a wide spectrum of adrenergic-related symptoms. To determine the aetiology of POTS, we examined a possible pathophysiological role for autoantibodies against α1-adrenergic (α1AR) and ß1/2-adrenergic receptors (ß1/2AR). METHODS AND RESULTS: Immunoglobulin G (IgG) derived from 17 POTS patients, 7 with recurrent vasovagal syncope (VVS), and 11 normal controls was analysed for its ability to modulate activity and ligand responsiveness of α1AR and ß1/2AR in transfected cells and to alter contractility of isolated rat cremaster arterioles in vitro. Immunoglobulin G activation of α1AR and ß1/2AR was significantly higher in POTS compared with VVS and controls in cell-based assays. Eight, 11, and 12 of the 17 POTS patients possessed autoantibodies that activated α1AR, ß1AR and ß2AR, respectively. Pharmacological blockade suppressed IgG-induced activation of α1AR and ß1/2AR. Eight of 17 POTS IgG decreased the α1AR responsiveness to phenylephrine and 13 of 17 POTS IgG increased the ß1AR responsiveness to isoproterenol irrespective of their ability to directly activate their receptors. Postural tachycardia syndrome IgG contracted rat cremaster arterioles, which was reversed by α1AR blockade. The upright heart rate correlated with IgG-mediated ß1AR and α1AR activity but not with ß2AR activity. CONCLUSION: These data confirm a strong relationship between adrenergic autoantibodies and POTS. They support the concept that allosteric-mediated shifts in the α1AR and ß1AR responsiveness are important in the pathophysiology of postural tachycardia.

The structural basis for agonist and partial agonist action on a ß(1)-adrenergic receptor.

ß-adrenergic receptors (ßARs) are G-protein-coupled receptors (GPCRs) that activate intracellular G proteins upon binding catecholamine agonist ligands such as adrenaline and noradrenaline. Synthetic ligands have been developed that either activate or inhibit ßARs for the treatment of asthma, hypertension or cardiac dysfunction. These ligands are classified as either full agonists, partial agonists or antagonists, depending on whether the cellular response is similar to that of the native ligand, reduced or inhibited, respectively. However, the structural basis for these different ligand efficacies is unknown. Here we present four crystal structures of the thermostabilized turkey (Meleagris gallopavo) ß(1)-adrenergic receptor (ß(1)AR-m23) bound to the full agonists carmoterol and isoprenaline and the partial agonists salbutamol and dobutamine. In each case, agonist binding induces a 1 Å contraction of the catecholamine-binding pocket relative to the antagonist bound receptor. Full agonists can form hydrogen bonds with two conserved serine residues in transmembrane helix 5 (Ser(5.42) and Ser(5.46)), but partial agonists only interact with Ser(5.42) (superscripts refer to Ballesteros-Weinstein numbering). The structures provide an understanding of the pharmacological differences between different ligand classes, illuminating how GPCRs function and providing a solid foundation for the structure-based design of novel ligands with predictable efficacies.

Nebivolol suppresses cardiac ryanodine receptor-mediated spontaneous Ca2+ release and catecholaminergic polymorphic ventricular tachycardia.

ß-Blockers are a standard treatment for heart failure and cardiac arrhythmias. There are ∼30 commonly used ß-blockers, representing a diverse class of drugs with different receptor affinities and pleiotropic properties. We reported that among 14 ß-blockers tested previously, only carvedilol effectively suppressed cardiac ryanodine receptor (RyR2)-mediated spontaneous Ca2+ waves during store Ca2+ overload, also known as store overload-induced Ca2+ release (SOICR). Given the critical role of SOICR in arrhythmogenesis, it is of importance to determine whether there are other ß-blockers that suppress SOICR. Here, we assessed the effect of other commonly used ß-blockers on RyR2-mediated SOICR in HEK293 cells, using single-cell Ca2+ imaging. Of the 13 ß-blockers tested, only nebivolol, a ß-1-selective ß-blocker with nitric oxide synthase (NOS)-stimulating action, effectively suppressed SOICR. The NOS inhibitor (N-nitro-l-arginine methyl ester) had no effect on nebivolol's SOICR inhibition, and the NOS activator (histamine or prostaglandin E2) alone did not inhibit SOICR. Hence, nebivolol's SOICR inhibition was independent of NOS stimulation. Like carvedilol, nebivolol reduced the opening of single RyR2 channels and suppressed spontaneous Ca2+ waves in intact hearts and catecholaminergic polymorphic ventricular tachycardia (CPVT) in the mice harboring a RyR2 mutation (R4496C). Interestingly, a non-ß-blocking nebivolol enantiomer, (l)-nebivolol, also suppressed SOICR and CPVT without lowering heart rate. These data indicate that nebivolol, like carvedilol, possesses a RyR2-targeted action that suppresses SOICR and SOICR-evoked VTs. Thus, nebivolol represents a promising agent for Ca2+-triggered arrhythmias.

Dobutamine, a ß1 Adrenoceptor Agonist, Increases Cerebral Oxygenation During Acute Anemia and Apneic Hypoxia.

BACKGROUND: ß1 blockers increase the risk of cerebral hypoxia during acute anemia and apneic hypoxia. We hypothesized that ß1 stimulants conversely increase cerebral tolerance to anemia and hypoxia. METHODS: After induction with isoflurane, twelve swine (mean ± SD: 25.2 ± 0.6 kg) received 200 µg kg-1 min-1 landiolol and 20 µg kg-1 min-1 dobutamine. Reversal of the order of drug administration was performed in six animals each. Before and during each drug infusion, apnea was induced until reaching <70% oxygen saturation (SpO2) after 5 min of 100% oxygen ventilation. Hemodynamic and blood gas variables were measured, and the cerebral and peripheral tissue oxygenation index (TOI) was recorded by near-infrared spectroscopy (apnea experiment). Following this, anemia (isovolemic hemodilution) was induced and apnea experiments were conducted in three stages, similarly to those before anemia. RESULTS: Dobutamine increased cerebral TOI before apnea (fraction of inspired oxygen [FiO2]: 1.0), at 1 min after apnea, and at SpO2 < 70% by 7.9, 8.8, and 3.9%. Landiolol decreased TOI by 0.8, 2.6, and 4.4% from the respective values at baseline. During anemia, these changes decreased with dobutamine and increased with landiolol administration. Dobutamine (or landiolol) shifted the relationship between TOI and arterial hemoglobin oxygen saturation or arterial partial pressure of oxygen to the right (or left) and increased (or decreased) TOI at similar arterial blood oxygenation. CONCLUSIONS: Dobutamine increases cerebral oxygenation during hypoxia and/or anemia and might be effective in improving neurological outcomes in ischemic cerebral injury.

Simulation of the effects of moderate stimulation/inhibition of the ß1-adrenergic signaling system and its components in mouse ventricular myocytes.

The ß1-adrenergic signaling system is one of the most important protein signaling systems in cardiac cells. It regulates cardiac action potential duration, intracellular Ca(2+) concentration ([Ca(2+)]i) transients, and contraction force. In this paper, a comprehensive experimentally based mathematical model of the ß1-adrenergic signaling system for mouse ventricular myocytes is explored to simulate the effects of moderate stimulations of ß1-adrenergic receptors (ß1-ARs) on the action potential, Ca(2+) and Na(+) dynamics, as well as the effects of inhibition of protein kinase A (PKA) and phosphodiesterase of type 4 (PDE4). Simulation results show that the action potential prolongations reach saturating values at relatively small concentrations of isoproterenol (∼0.01 µM), while the [Ca(2+)]i transient amplitude saturates at significantly larger concentrations (∼0.1-1.0 µM). The differences in the response of Ca(2+) and Na(+) fluxes to moderate stimulation of ß1-ARs are also observed. Sensitivity analysis of the mathematical model is performed and the model limitations are discussed. The investigated model reproduces most of the experimentally observed effects of moderate stimulation of ß1-ARs, PKA, and PDE4 inhibition on the L-type Ca(2+) current, [Ca(2+)]i transients, and the sarcoplasmic reticulum Ca(2+) load and makes testable predictions for the action potential duration and [Ca(2+)]i transients as functions of isoproterenol concentration.