Enhanced cAMP-induced nitric oxide-dependent coronary dilation during myocardial stunning in conscious pigs

Hypoxia and hyperoxia potentiate PAF receptor-mediated effects in newborn ovine pulmonary arterial smooth muscle cells: significance in oxygen therapy of PPHN

Platelet-activating factor (PAF) acting via its receptor (PAFR) is implicated in the pathogenesis of persistent pulmonary hypertension of the newborn (PPHN). Effects of long-term oxygen therapy on newborn lung are not well understood; therefore, we studied the effect of oxygen tension on ovine newborn pulmonary artery smooth muscle cells (NBPASMC). Our global hypothesis is that PPHN results from failure of newborn lamb pulmonary system to downregulate PAFR activity or to upregulate vasodilatory cyclic nucleotides (Cnucs) activity. NBPASMC from newborns 6-12 days old were studied in vitro at three different oxygen tensions (pO2, [Torr]: hypoxia, <40; normoxia, 80-100; and hyperoxia, >100 Torr often clinically imposed upon newborns with PPHN) PAFR- and Cnucs mediated effects were determined. PAFR and PKA Cα mRNA expression as well as prostacyclin, thromboxane, cAMP production, and DNA synthesis was studied to assess PAFR-mediated hypertrophy and/or hyperplasia. Hypoxia and hyperoxia increased specific PAFR binding. PAF treatment during hyperoxia increased PAFR gene, but decreased PKA-Cα gene expression. Hypoxia and hyperoxia increased NBPASMC proliferation via PAFR signaling. Baseline prostacyclin level was ninefold greater than in fetal PASMC, whereas baseline thromboxane was sevenfold less suggesting greater postnatal cyclooxygenase activity in NBPASMC PAF decreased, while forskolin and 8-Br-cAMP increased cAMP production. Decrease of PAFR effects by Cnucs indicates that normal newborn PA physiology favors vasodilator pathways to minimize PAF-induced hypertrophy or hyperplasia. We speculate that failure of newborn lung to anchor downregulation of vasoconstrictors with upregulation of vasodilators leads to PPHN.

Differential effects of selective and non-selective nitric oxide synthase inhibitors on the blood perfusion of ischemia-reperfused myocardium in dogs

Background

Nitric oxide (NO) is protective for the cardiovascular system, and excessive NO exerts negative effects on the circulatory system. This study aimed to compare the effects of selective or non-selective NO synthase (NOS) inhibitors on blood flow perfusion of ischemia-reperfused myocardium.

Materials/Methods

Male mongrel dogs were randomly assigned to 4 groups: only ischemia-reperfusion (control), ischemia-reperfusion plus N^ω-nitro-L-arginine methyl ester (NAME) treatment, ischemia-reperfusion plus aminoguanidine (AMD) treatment, and sham operation group. Myocardial contrast echocardiography (MCE) was performed. Blood samples were taken for measurement of NO. Background-subtracted peak videointensity (PVI) and PVI ratio in myocardium were measured.

Results

In the NAME-treated group, the PVI at 5 min reperfusion did not significantly differ from pre-LAD-occlusion, but declined to and retained at a level obviously lower than the pre-LAD-occlusion. In the AMD-treated group, the PVI at 5 min reperfusion was significantly higher than at pre-LAD-occlusion, and then restored to and remained at the pre-LAD-occlusion level. The changes of PVI ratios in the 3 groups were similar to PVI values. In the AMD-treated group, the curve width increased in the early reperfusion, but returned to the pre-LAD-occlusion level at 90 min reperfusion. The plasma NO concentration in the NAME-treated group greatly decreased and remained low during the whole period of reperfusion. In the AMD-treated group, there were only slight increases in NO concentrations during reperfusion.

Conclusions

NAME totally inhibited NO production and attenuated myocardial blood flow perfusion. Aminoguanidine significantly relieved the increase in NO production and alleviated the congestion of reperfused myocardium. Selective inhibitors of iNOS might be useful in the management of certain diseases associated with ischemia-reperfusion.

Pharmacology of levosimendan: inotropic, vasodilatory and cardioprotective effects

WHAT IS KNOWN AND OBJECTIVE

Positive inotropic agents are frequently used in acute decompensated heart failure (ADHF) due to left ventricular systolic dysfunction. These agents are known to improve cardiac performance and peripheral perfusion in the short-term treatment. However, several preclinical and clinical studies emphasized detrimental effects of these drugs on myocardial oxygen demand and on sympathetic tone entailing arrhythmogenesis. Levosimendan is an inotropic agent with an original mechanism of action. This review focuses on major data available for levosimendan.

METHODS

A literature search was conducted in the PubMed database by including studies published in English using combinations of the following key words, levosimendan, inotropic drugs and acute heart failure. Furthermore, bibliographies of selected references were also evaluated for relevant articles. The collection for this review was limited to the most recently available human and animal data.

RESULTS AND DISCUSSION

Levosimendan's vasodilatory and cardioprotective effects are mediated by calcium sensitization of contractile proteins and opening of adenosine triphosphate (ATP)-dependent K+ channels in vascular smooth muscle cells and on mitochondrial ATP-sensitive potassium [mito.K(ATP)] channels. This inotropic agent has mild PDE inhibitory action. Unlike other inotropic agents, levosimendan improves cardiac performance without activating the sympathetic nervous system. Moreover, there are evidences that levosimendan has additional anti-inflammatory and anti-apoptotic properties that prevent cardiac toxicity and contributes to positive hemodynamic response of the drug. Four randomized trials evaluated the effects of levosimendan on mortality in patients with acute decompensated chronic heart failure; nevertheless, a clear benefit has not been demonstrated so far. Although levosimendan is indicated for the treatment of ADHF (class of recommendation IIa, level of evidence B), it is has not been approved in all countries.

WHAT IS NEW AND CONCLUSION

This review summarizes the characteristics and the current knowledge of the literature on levosimendan and its active metabolite OR-1896.

Caffeine restores myocardial cytochrome oxidase activity and improves cardiac function during sepsis

OBJECTIVE

Impaired mitochondrial function is a potential cause of sepsis-associated myocardial depression. Cytochrome oxidase (CcOX), the terminal oxidase of the electron transport chain, is inhibited in the septic heart. Caffeine increases CcOX activity by increasing cyclic adenosine monophosphate and protein kinase A activity. We hypothesized that caffeine will restore myocardial CcOX activity, increase cardiac function, and improve survival during sepsis.

DESIGN

Prospective randomized controlled study.

SETTING

University hospital-based laboratory.

SUBJECTS

One hundred twenty Sprague-Dawley male rats.

INTERVENTIONS

Sprague-Dawley male rats underwent cecal ligation and puncture (CLP) or sham operation. At 24 and 48 hours, rats underwent intraperitoneal injection of either caffeine (7.5 mg/kg, the equivalent of 1-1.5 cups of coffee) or equal volume of saline.

MEASUREMENTS AND MAIN RESULTS

One hour following the 48-hour injection, steady-state CcOX kinetic activity was measured in isolated mitochondria and normalized to citrate synthase activity. Cardiac function was assessed using an isolated rat heart preparation and survival was tracked to 96 hours. CLP significantly decreased myocardial CcOX activity, oxygen consumption, left ventricular pressure, and pressure developed during isovolumic contraction (+dP/dt) and relaxation (-dP/dt). Caffeine restored CcOX activity and increased left ventricular pressure and +/-dP/dt toward sham values following CLP. Survival significantly improved following CLP in caffeine-injected animals compared with saline injection.

CONCLUSION

Caffeine may be a novel therapy to treat sepsis-associated myocardial depression.

Pivotal effects of phosphodiesterase inhibitors on myocyte contractility and viability in normal and ischemic hearts

Phosphodiesterases (PDEs) are enzymes that degrade cellular cAMP and cGMP and are thus essential for regulating the cyclic nucleotides. At least 11 families of PDEs have been identified, each with a distinctive structure, activity, expression, and tissue distribution. The PDE type-3, -4, and -5 (PDE3, PDE4, PDE5) are localized to specific regions of the cardiomyocyte, such as the sarcoplasmic reticulum and Z-disc, where they are likely to influence cAMP/cGMP signaling to the end effectors of contractility. Several PDE inhibitors exhibit remarkable hemodynamic and inotropic properties that may be valuable to clinical practice. In particular, PDE3 inhibitors have potent cardiotonic effects that can be used for short-term inotropic support, especially in situations where adrenergic stimulation is insufficient. Most relevant to this review, PDE inhibitors have also been found to have cytoprotective effects in the heart. For example, PDE3 inhibitors have been shown to be cardioprotective when given before ischemic attack, whereas PDE5 inhibitors, which include three widely used erectile dysfunction drugs (sildenafil, vardenafil and tadalafil), can induce remarkable cardioprotection when administered either prior to ischemia or upon reperfusion. This article provides an overview of the current laboratory and clinical evidence, as well as the cellular mechanisms by which the inhibitors of PDE3, PDE4 and PDE5 exert their beneficial effects on normal and ischemic hearts. It seems that PDE inhibitors hold great promise as clinically applicable agents that can improve cardiac performance and cell survival under critical situations, such as ischemic heart attack, cardiopulmonary bypass surgery, and heart failure.

Pharmacological preconditioning by levosimendan is mediated by inducible nitric oxide synthase and mitochondrial KATP channel activation in the in vivo anesthetized rabbit heart model

BACKGROUND

Provocation of fatal cardiac arrhythmias has limited the use of inotropic agents as heart failure therapy. Levosimendan (LEV) is a new inodilator, whose mechanism of action includes calcium sensitization of contractile proteins and the opening of ATP-dependent potassium channels.

OBJECTIVES AND METHODS

The aim of this investigation was to test whether the administration of LEV has cardioprotective and antiarrhythmic effects against ischemia and reperfusion injury in a manner similar to ischemic preconditioning (IPC) in a well-standardized model of reperfusion arrhythmias in anesthetized adult male rabbits (n=122) subjected to 30 min occlusion of the left coronary artery followed by 120 min of reperfusion.

RESULTS

Pretreatment with either 1 cycle of IPC, LEV (0.1 micromol/kg, i.v.), or IPC+LEV prior to the period of coronary occlusion offers significant infarct size reduction (21.6+/-1.6%, 22.1+/-2.2%, and 21.4+/-1.4%, respectively vs 38.7+/-3.6% in saline control group; P<0.01) and antiarrhythmic effects. IPC, LEV and IPC+LEV treatment significantly attenuated the incidence of life-threatening arrhythmias like sustained VT (13%, 13% and 13%, respectively vs 100% in saline control group; P<0.005) and other arrhythmias (25%, 25% and 13%, respectively vs 100% in saline control group; P<0.005), and increased the number of surviving animals without arrhythmias. Pretreatment with 5-HD, N(omega)-nitro-L-arginine methyl ester (L-NAME, a nonspecific NOS inhibitor) and the specific iNOS inhibitor 1400 W [N-(-3-(aminomethyl)benzyl) acetamidine] abolished the beneficial effects of IPC, and LEV on reperfusion induced arrhythmias and cardioprotection suggesting that benefits have been achieved via both the selective activation of cardiomyocyte mitochondrial K(ATP) channels and NO. One cycle of IPC and LEV pretreatment significantly preserved the level of ATP in the 30 min ischemic heart and 120 min reperfused heart.

CONCLUSIONS

The present study demonstrates similarities between acute LEV treatment and IPC of the rabbit myocardium in terms of survival, cardioprotection, antiarrhythmic activity, and metabolic status.

Obligatory role of cardiac nerves and alpha1-adrenergic receptors for the second window of ischemic preconditioning in conscious pigs

We tested the hypothesis that cardiac nerves may mediate ischemic preconditioning. Pigs were chronically instrumented to measure aortic, left atrial and left ventricular pressures, and regional myocardial function (wall thickening). Hemodynamic variables, area at risk, and tissue blood flows (radioactive microspheres) were similar among groups. Myocardial infarct size following 60 minutes coronary artery occlusion and 4 days reperfusion, expressed as a fraction of the area at risk, was 42+/-4.0%, in innervated pigs and similar in pigs with regional cardiac denervation (CD, 41+/-2.5%). Infarct size in innervated pigs during the first window of preconditioning (first window) was markedly reduced (6+/-1.8%, P<0.01), as it was in the second window of preconditioning (second window) (16+/-3.3%, P<0.01). Although infarct size was still reduced in pigs with CD and first window preconditioning (9+/-1.8%, P<0.01), the protective effects of second window were abrogated in pigs with CD resulting in an infarct size of 38+/-5.6%. In another group of innervated pigs during pharmacological alpha(1)-adrenergic receptor (AR) blockade, infarct size was also not reduced during the second window (48+/-3.2%). Additionally, Western blot analysis of inducible nitric oxide synthase and cyclooxygenase-2 proteins demonstrated significant (P<0.05) upregulation following the second window in innervated pigs, but not in pigs with CD or alpha(1)-AR blockade. Thus, the mechanism of protection during the second window, but not the first window, appears to be dependent on cardiac nerves and alpha(1)-AR stimulation.

cAMP signal transduction induces eNOS activation by promoting PKB phosphorylation

The objective of this study was to determine whether activation of protein kinase B (PKB) is involved in the production of nitric oxide (NO) induced by cAMP signal transduction. Mongrel dogs were used for this study. Coronary microvessels were isolated from the left ventricular free wall of these dog hearts. Forskolin (an activator of adenylyl cyclase that increases intracellular cAMP level) and 8-bromo-cAMP (a membrane-permeable cAMP analog) were used to stimulate NO release and activation of PKB and endothelial NO synthase (eNOS) in these blood vessels. We found that forskolin and 8-bromo-cAMP increased NO release (quantified by using the Griess reaction) from coronary microvessels by 80 +/- 6 and 78 +/- 11 pmol/mg (mean +/- SE), respectively (P < 0.05 vs. control). Western blot analysis showed that forskolin elicited a significant increase in eNOS phosphorylation (59 +/- 11%) at serine-1177 (a positively regulatory phosphorylation site for eNOS) and a significant increase in dephosphorylation (28 +/- 6%) at threonine-495 (a negatively regulatory phosphorylation site of eNOS) (P < 0.05 vs. control). Interestingly, forskolin also increased the phosphorylation of PKB at serine-473 (by 49 +/- 17%) and threonine-308 (by 53 +/- 17%), respectively (P < 0.05 vs. control; phosphorylation of both sites is required for a full activation of PKB). N(omega)-nitro-l-arginine methyl ester (an NOS inhibitor) blocked NO formation, Rp diastereomer of cAMP (a PKA inhibitor), and LY-294002 [a PI3-kinase (an activator of PKB) inhibitor] prevented the production of NO, phosphorylation of PKB, and eNOS induced by forskolin. Our data clearly show an involvement of PKB activation in cAMP signal-induced NO production. We are reporting for the first time that cAMP signal transduction stimulates eNOS activation through a PKB-mediated mechanism.

The cellular mechanisms by which adenosine evokes release of nitric oxide from rat aortic endothelium

Adenosine and nitric oxide (NO) are important local mediators of vasodilatation. The aim of this study was to elucidate the mechanisms underlying adenosine receptor-mediated NO release from the endothelium. In studies on freshly excised rat aorta, second-messenger systems were pharmacologically modulated by appropriate antagonists while a NO-sensitive electrode was used to measure adenosine-evoked NO release from the endothelium. We showed that A1-mediated NO release requires extracellular Ca2+, phospholipase A2 (PLA2) and ATP-sensitive K+ (KATP) channel activation whereas A2A-mediated NO release requires extracellular Ca2+ and Ca2+-activated K+ (KCa) channels. Since our previous study showed that A1- and A2A-receptor-mediated NO release requires activation of adenylate cyclase (AC), we propose the following novel pathways. The K+ efflux resulting from A1-receptor-coupled KATP-channel activation facilitates Ca2+ influx which may cause some stimulation of endothelial NO synthase (eNOS). However, the increase in [Ca2+]i also stimulates PLA2 to liberate arachidonic acid and stimulate cyclooxygenase to generate prostacyclin (PGI2). PGI2 acts on its endothelial receptors to increase cAMP, so activating protein kinase A (PKA) to phosphorylate and activate eNOS resulting in NO release. By contrast, the K+ efflux resulting from A2A-coupled KCa channels facilitates Ca2+ influx, thereby activating eNOS and NO release. This process may be facilitated by phosphorylation of eNOS by PKA via the action of A2A-receptor-mediated stimulation of AC increasing cAMP. These pathways may be important in mediating vasodilatation during exercise and systemic hypoxia when adenosine acting in an endothelium- and NO-dependent manner has been shown to be important.

Aldosterone Regulates Vascular Reactivity

Background— There is increasing evidence for rapid nongenomic effects of aldosterone. Therefore, we studied the immediate effects of aldosterone on vascular reactivity in rat aortic ring segments and on endothelial and vascular smooth muscle cellular responses.

Methods and Results— In endothelium-intact ring segments, aldosterone attenuated phenylephrine-mediated constriction (maximal reduction, 25±4% below control phenylephrine-mediated constriction). In contrast, in endothelium-denuded vessels, aldosterone mediated a monophasic dose-dependent enhancement of vasoconstrictor response. In endothelial cells, aldosterone caused a phosphatidylinositol 3-kinase (PI3K)–dependent increase in nitric oxide synthase activity as well as PI3K-dependent activation of extracellular signal–regulated kinase 1/2 and p70 S6 kinase.

Conclusions— Overall, these data support a novel effect of aldosterone on vascular endothelial and smooth muscle cell function. These rapid effects of aldosterone might be important in both the short- and long-term regulation of peripheral vascular resistance. Furthermore, in the setting of endothelial dysfunction, alterations in aldosterone’s short-term vascular responses might contribute to its pathophysiological effects in cardiovascular disease.

Cardiac nerves affect myocardial stunning through reactive oxygen and nitric oxide mechanisms

The goal of this study was to investigate the role of cardiac nerves on the response to 90-minute coronary artery stenosis (CAS), which reduced coronary blood flow by 40% for 90 minutes, and subsequent myocardial stunning after reperfusion in chronically instrumented conscious pigs. In pigs with regional cardiac denervation (CD), myocardial stunning was intensified, ie, at 12 hours reperfusion wall thickening (WT) was depressed more, P<0.05, in CD (-46+/-5%) as compared with intact pigs (-31+/-3%) and remained depressed in CD at 24 hours reperfusion (-45+/-6%). Although the TTC technique was negative for infarct, histopathological analysis revealed patchy necrosis present in 11+/-2% of the area at risk. In intact pigs, WT had essentially recovered at 24 hours without infarct. In CD pigs treated with either an antioxidant, N-2-mercaptopropionyl glycine (MPG, 100 mg/kg per hour) or systemic nitric oxide synthase inhibition using N(omega)-nitro-L-arginine (L-NA, 30 mg/kg for 3 days), recovery of wall thickening was similar to that in pigs with intact nerves and without evidence of infarct. Immunohistochemistry analysis for 3-nitrotyrosine in tissue after CAS and 1 hour reperfusion demonstrated enhanced peroxynitrite-related protein nitration in pigs with regional CD compared with pigs with intact cardiac nerves, and pigs with regional CD and MPG or L-NA. Thus, reperfusion after myocardial ischemia in the setting of CD results in enhanced stunning and development of infarct. The underlying mechanism appears to involve nitric oxide and reactive oxygen species.

cAMP signal transduction, a potential compensatory pathway for coronary endothelial NO production after heart failure

OBJECTIVE

This study investigated whether cAMP signal transduction regulates coronary microvascular NO production after heart failure (HF), a state in which endothelial NO synthase (eNOS) is downregulated.

METHODS AND RESULTS

Myocardial microvessels were isolated. Nitrite, the hydration product of NO, from these vessels was quantified by using the Griess reaction. Forskolin (10(-4) mol/L), 8-bromo-cAMP (10(-2) mol/L), isoproterenol (10(-4) mol/L), or adrenomedullin (10(-6) mol/L) significantly increased nitrite release by 78+/-8, 84+/-14, 71+/-11, and 73+/-15 pmol/mg, respectively, from isolated microvessels from normal canine hearts (P<0.05 versus control). Bradykinin (10(-5) mol/L) and acetylcholine (10(-5) mol/L) increased nitrite release by 83+/-13 and 72+/-6 pmol/mg, respectively (P<0.05 versus control). However, NO production induced by bradykinin and acetylcholine was markedly reduced after HF (46+/-7 and 39+/-7 pmol/mg, respectively; P<0.05 versus normal), reflecting eNOS downregulation (55% in eNOS protein). Surprisingly, NO production in response to forskolin, 8-bromo-cAMP, isoproterenol, and adrenomedullin not only was preserved but also was substantially enhanced in these microvessels after HF (121+/-14, 124+/-21, 107+/-18, and 122+/-16 pmol/mg, respectively; P<0.05 versus normal group) and was associated with an upregulation of protein kinase B (220% increase in protein kinase B protein). All these responses were in an NO synthase or a protein kinase A inhibitor-blockable manner.

CONCLUSIONS

Our data indicate that cAMP signal transduction may be an important potential compensatory pathway to increase myocardial microvascular NO production after HF when eNOS is downregulated.

cAMP signal transduction cascade, a novel pathway for the regulation of endothelial nitric oxide production in coronary blood vessels

The aim of this study was to determine whether cAMP signal transduction plays a role in the regulation of endothelial nitric oxide (NO) production. Canine coronary blood vessels were isolated, and nitrite, the hydration product of NO, from these vessels was quantified by using the Griess reaction. Forskolin (10(-4) mol/L), 8-bromo-cAMP (10(-2) mol/L), or isoproterenol (10(-4) mol/L) significantly increased nitrite release to 168+/-10, 162+/-13, or 149+/-13 pmol/mg, respectively, from isolated coronary microvessels (all P<0.05; control, 86+/-3 pmol/mg). Adrenomedullin and calcitonin gene-related peptide (CGRP), both potent vasodilator peptides, also increased coronary microvascular nitrite production. N(omega)-nitro-L-arginine methyl ester, a competitive inhibitor of NO synthase, or Rp-cAMP, a protein kinase A inhibitor, markedly blocked the nitrite release induced by these agents. Forskolin and adrenomedullin also potentiated coronary NO production induced by bradykinin. In large coronary arteries, removal of the endothelium eliminated nitrite production to both forskolin and acetylcholine. Our data demonstrate that stimulation of cAMP signal transduction can substantially increase coronary NO production, indicating that there is a cAMP-mediated, endothelial NO-forming system in coronary blood vessels. Because the cAMP signal cascade can be activated by CGRP or adrenomedullin and enhance kinin-mediated nitrite production, the cAMP-NO pathway may play an important role in the regulation of cardiovascular function.