Is lipid signaling through cannabinoid 2 receptors part of a protective system?

The mammalian body has a highly developed immune system which guards against continuous invading protein attacks and aims at preventing, attenuating or repairing the inflicted damage. It is conceivable that through evolution analogous biological protective systems have been evolved against non-protein attacks. There is emerging evidence that lipid endocannabinoid signaling through cannabinoid 2 (CB₂) receptors may represent an example/part of such a protective system/armamentarium. Inflammation/tissue injury triggers rapid elevations in local endocannabinoid levels, which in turn regulate signaling responses in immune and other cells modulating their critical functions. Changes in endocannabinoid levels and/or CB₂ receptor expressions have been reported in almost all diseases affecting humans, ranging from cardiovascular, gastrointestinal, liver, kidney, neurodegenerative, psychiatric, bone, skin, autoimmune, lung disorders to pain and cancer, and modulating CB₂ receptor activity holds tremendous therapeutic potential in these pathologies. While CB₂ receptor activation in general mediates immunosuppressive effects, which limit inflammation and associated tissue injury in large number of pathological conditions, in some disease states activation of the CB₂ receptor may enhance or even trigger tissue damage, which will also be discussed alongside the protective actions of the CB₂ receptor stimulation with endocannabinoids or synthetic agonists, and the possible biological mechanisms involved in these effects.

Role of the peroxynitrite-poly(ADP-ribose) polymerase pathway in human disease

Throughout the last 2 decades, experimental evidence from in vitro studies and preclinical models of disease has demonstrated that reactive oxygen and nitrogen species, including the reactive oxidant peroxynitrite, are generated in parenchymal, endothelial, and infiltrating inflammatory cells during stroke, myocardial and other forms of reperfusion injury, myocardial hypertrophy and heart failure, cardiomyopathies, circulatory shock, cardiovascular aging, atherosclerosis and vascular remodeling after injury, diabetic complications, and neurodegenerative disorders. Peroxynitrite and other reactive species induce oxidative DNA damage and consequent activation of the nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP-1), the most abundant isoform of the PARP enzyme family. PARP overactivation depletes its substrate NAD(+), slowing the rate of glycolysis, electron transport, and ATP formation, eventually leading to functional impairment or death of cells, as well as up-regulation of various proinflammatory pathways. In related animal models of disease, peroxynitrite neutralization or pharmacological inhibition of PARP provides significant therapeutic benefits. Therefore, novel antioxidants and PARP inhibitors have entered clinical development for the experimental therapy of various cardiovascular and other diseases. This review focuses on the human data available on the pathophysiological relevance of the peroxynitrite-PARP pathway in a wide range of disparate diseases, ranging from myocardial ischemia/reperfusion injury, myocarditis, heart failure, circulatory shock, and diabetic complications to atherosclerosis, arthritis, colitis, and neurodegenerative disorders.

Cardiovascular effects of marijuana and synthetic cannabinoids: the good, the bad, and the ugly

Dysregulation of the endogenous lipid mediators endocannabinoids and their G-protein-coupled cannabinoid receptors 1 and 2 (CB1R and CB2R) has been implicated in a variety of cardiovascular pathologies. Activation of CB1R facilitates the development of cardiometabolic disease, whereas activation of CB2R (expressed primarily in immune cells) exerts anti-inflammatory effects. The psychoactive constituent of marijuana, Δ9-tetrahydrocannabinol (THC), is an agonist of both CB1R and CB2R, and exerts its psychoactive and adverse cardiovascular effects through the activation of CB1R in the central nervous and cardiovascular systems. The past decade has seen a nearly tenfold increase in the THC content of marijuana as well as the increased availability of highly potent synthetic cannabinoids for recreational use. These changes have been accompanied by the emergence of serious adverse cardiovascular events, including myocardial infarction, cardiomyopathy, arrhythmias, stroke, and cardiac arrest. In this Review, we summarize the role of the endocannabinoid system in cardiovascular disease, and critically discuss the cardiovascular consequences of marijuana and synthetic cannabinoid use. With the legalization of marijuana for medicinal purposes and/or recreational use in many countries, physicians should be alert to the possibility that the use of marijuana or its potent synthetic analogues might be the underlying cause of severe cardiovascular events and pathologies.

Cardiovascular side effects of new antidepressants and antipsychotics: new drugs, old concerns?

The cardiovascular toxicity of older generation of tricyclic antidepressants (e.g. imipramine, desipramine, amitriptyline, clomipramine) and neuroleptics (e.g. haloperidol, droperidol, thioridazine, pimozide) is well established. These drugs inhibit cardiovascular Na(+), Ca(2+) and K(+) channels often leading to life-threatening arrhythmia. To overcome the toxicity of old generation of antidepressants and antipsychotics, selective serotonin reuptake inhibitor antidepressants (SSRIs: fluoxetine, fluvoxamine, paroxetine, sertraline, citalopram, venlafaxin) and several new antipsychotics (e.g. clozapine, olanzapine, risperidone, sertindole, aripiprazole, ziprasidone, quetiapine) were introduced during the past decade. Although these new compounds are not more effective in treating psychiatric disorders than older medications, they gained incredible popularity since they have been reported to have fewer and more benign side effect profile (including cardiovascular) than predecessors. Surprisingly, an increasing number of case reports have demonstrated that the use of SSRIs and new antipsychotics (e.g. clozapine, olanzapine, risperidone, sertindole, aripiprazole, ziprasidone, quetiapine) is associated with cases of arrhythmias, prolonged QTc interval on electrocardiogram (ECG) and orthostatic hypotension in patients lacking cardiovascular disorders, raising new concerns about the putative cardiovascular safety of these compounds. In agreement with these clinical reports these new compounds indeed show marked cardiovascular depressant effects in different mammalian and human cardiovascular preparations by inhibiting cardiac and vascular Na(+), Ca(2+) and K(+) channels. Taken together, these results suggest that the new generation of antidepressants and antipsychotics also have clinically important cardiac as well as vascular effects. Clinicians should be more vigilant about these potential adverse reactions and ECG control may be suggested during therapy, especially in patients with cardiovascular disorders. The primary goal of this review is to shed light on the recently observed clinically important cardiovascular effects of new antidepressants and antipsychotics and discuss the mechanism beyond this phenomenon.

The role of poly(ADP-ribose) polymerase activation in the development of myocardial and endothelial dysfunction in diabetes

Patients with diabetes exhibit a high incidence of diabetic cardiomyopathy and vascular complications, which underlie the development of retinopathy, nephropathy, and neuropathy and increase the risk of hypertension, stroke, and myocardial infarction. There is emerging evidence that the activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) importantly contributes to the development of endothelial dysfunction in a streptozotocin-induced model of diabetes. We investigated the role of PARP activation in the pathogenesis of cardiac dysfunction in streptozotocin-induced and genetic (nonobese diabetic) models of diabetes in rats and mice. Development of diabetes was accompanied by hyperglycemia, cardiac PARP activation, a selective loss of endothelium-dependent vasodilation in the thoracic aorta, and an early diastolic dysfunction of the heart. Treatment with a novel potent phenanthridinone-based PARP inhibitor, PJ34, starting 1 week after the onset of diabetes, restored normal vascular responsiveness and significantly improved cardiac dysfunction, despite the persistence of severe hyperglycemia. The beneficial effect of PARP inhibition persisted even after several weeks of discontinuation of the treatment. Thus, PARP activation plays a central role in the pathogenesis of diabetic cardiovascular (cardiac as well as endothelial) dysfunction. PARP inhibitors may exert beneficial effects against the development of cardiovascular complications in diabetes.

Nitrosative stress and pharmacological modulation of heart failure

Dysregulation of nitric oxide (NO) and increased oxidative and nitrosative stress are implicated in the pathogenesis of heart failure. Peroxynitrite is a reactive oxidant that is produced from the reaction of nitric oxide with superoxide anion and impairs cardiovascular function through multiple mechanisms, including activation of matrix metalloproteinases (MMPs) and nuclear enzyme poly(ADP-ribose) polymerase (PARP). Recent studies suggest that the neutralization of peroxynitrite or pharmacological inhibition of MMPs and PARP are promising new approaches in the experimental therapy of various forms of myocardial injury. In this article, the role of nitrosative stress and downstream mechanisms, including activation of MMPs and PARP, in various forms of heart failure are discussed and novel emerging therapeutic strategies offered by neutralization of peroxynitrite and inhibition of MMPs and PARP in these pathophysiological conditions are reviewed.

Endocannabinoids and cannabinoid receptors in ischaemia-reperfusion injury and preconditioning

Ischaemia-reperfusion (I/R) is a pivotal mechanism of organ injury during stroke, myocardial infarction, organ transplantation and vascular surgeries. Ischaemic preconditioning (IPC) is a potent endogenous form of tissue protection against I/R injury. On the one hand, endocannabinoids have been implicated in the protective effects of IPC through cannabinoid CB1/CB2 receptor-dependent and -independent mechanisms. However, there is evidence suggesting that endocannabinoids are overproduced during various forms of I/R, such as myocardial infarction or whole body I/R associated with circulatory shock, and may contribute to the cardiovascular depressive state associated with these pathologies. Previous studies using synthetic CB1 receptor agonists or knockout mice demonstrated CB1 receptor-dependent protection against cerebral I/R injury in various animal models. In contrast, several follow-up reports have shown protection afforded by CB1 receptor antagonists, but not agonists. Excitedly, emerging studies using potent CB2 receptor agonists and/or knockout mice have provided compelling evidence that CB2 receptor activation is protective against myocardial, cerebral and hepatic I/R injuries by decreasing the endothelial cell activation/inflammatory response (for example, expression of adhesion molecules, secretion of chemokines, and so on), and by attenuating the leukocyte chemotaxis, rolling, adhesion to endothelium, activation and transendothelial migration, and interrelated oxidative/nitrosative damage. This review is aimed to discuss the role of endocannabinoids and CB receptors in various forms of I/R injury (myocardial, cerebral, hepatic and circulatory shock) and preconditioning, and to delineate the evidence supporting the therapeutic utility of selective CB2 receptor agonists, which are devoid of psychoactive effects, as a promising new approach to limit I/R-induced tissue damage.

Activation of poly(ADP-ribose) polymerase contributes to development of doxorubicin-induced heart failure

Activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) by oxidant-mediated DNA damage is an important pathway of cell dysfunction and tissue injury in conditions associated with oxidative stress. Increased oxidative stress is a major factor implicated in the cardiotoxicity of doxorubicin (DOX), a widely used antitumor anthracycline antibiotic. Thus, we hypothesized that the activation of PARP may contribute to the DOX-induced cardiotoxicity. Using a dual approach of PARP-1 suppression, by genetic deletion or pharmacological inhibition with the phenanthridinone PARP inhibitor PJ34, we now demonstrate the role of PARP in the development of cardiac dysfunction induced by DOX. PARP-1+/+ and PARP-1-/- mice received a single injection of DOX (25 mg/kg i.p). Five days after DOX administration, left ventricular performance was significantly depressed in PARP-1+/+ mice, but only to a smaller extent in PARP-1-/- ones. Similar experiments were conducted in BALB/c mice treated with PJ34 or vehicle. Treatment with a PJ34 significantly improved cardiac dysfunction and increased the survival of the animals. In addition PJ34 significantly reduced the DOX-induced increase in the serum lactate dehydrogenase and creatine kinase activities but not metalloproteinase activation in the heart. Thus, PARP activation contributes to the cardiotoxicity of DOX. PARP inhibitors may exert protective effects against the development of severe cardiac complications associated with the DOX treatment.

Trends in the development of new antidepressants. Is there a light at the end of the tunnel?

Since the introduction of tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs) in mid-1950's, treatment of depression has been dominated by monoamine hypotheses. The well-established clinical efficacy of TCAs and MAOIs is due, at least in part, to the enhancement of noradrenergic or serotonergic mechanisms, or to both. Unfortunately, their very broad mechanisms of action also include many unwanted effects related to their potent activity on cholinergic, adrenergic and histaminergic receptors. The introduction of selective serotonin reuptake inhibitors (SSRIs) over twenty years ago had been the next major step in the evolution of antidepressants to develop drugs as effective as the TCAs but of higher safety and tolerability profile. During the past two decades SSRIs (fluoxetine, fluvoxamine, paroxetine, sertraline, citalopram) gained incredible popularity and have become the most widely prescribed medication in the psychiatric practice. The evolution of antidepressants continued resulting in introduction of selective and reversible monoamine oxidase inhibitors (eg. moclobemid), selective noradrenaline (eg. reboxetine), dual noradrenaline and serotonin reuptake inhibitors (milnacipram, venlafaxin, duloxetin) and drugs with distinct neurochemical profiles such as mirtazapine, nefazadone and tianeptine. Different novel serotonin receptor ligands have also been intensively investigated. In spite of the remarkable structural diversity, most currently introduced antidepressants are 'monoamine based'. Furthermore, these newer agents are neither more efficacious nor rapid acting than their predecessors and approximately 30% of the population do not respond to current therapies. By the turn of the new millennium, we are all witnessing a result of innovative developmental strategies based on the better understanding of pathophysiology of depressive disorder. Several truly novel concepts have emerged suggesting that the modulation of neuropeptide (substance P, corticotrophin-releasing factor, neuropeptide Y, vasopressin V1b, melanin-concentrating hormone-1), N-methyl-D-aspartate, nicotinic acetylcholine, dopaminergic, glucocorticoid, delta-opioid, cannabinoid and cytokine receptors, gamma-amino butyric acid (GABA) and intracellular messenger systems, transcription, neuroprotective and neurogenic factors, may provide an entirely new set of potential therapeutic targets, giving hope that further major advances might be anticipated in the treatment of depressive disorder soon. The goal of this review is to give a brief overview of the major advances from monoamine-based treatment strategies, and particularly focus on the new emerging approaches in the treatment of depression.

Cardiovascular pharmacology of cannabinoids

Cannabinoids and their synthetic and endogenous analogs affect a broad range of physiological functions, including cardiovascular variables, the most important component of their effect being profound hypotension. The mechanisms of the cardiovascular effects of cannabinoids in vivo are complex and may involve modulation of autonomic outflow in both the central and peripheral nervous systems as well as direct effects on the myocardium and vasculature. Although several lines of evidence indicate that the cardiovascular depressive effects of cannabinoids are mediated by peripherally localized CB1 receptors, recent studies provide strong support for the existence of as-yet-undefined endothelial and cardiac receptor(s) that mediate certain endocannabinoid-induced cardiovascular effects. The endogenous cannabinoid system has been recently implicated in the mechanism of hypotension associated with hemorrhagic, endotoxic, and cardiogenic shock, and advanced liver cirrhosis. Furthermore, cannabinoids have been considered as novel antihypertensive agents. A protective role of endocannabinoids in myocardial ischemia has also been documented. In this chapter, we summarize current information on the cardiovascular effects of cannabinoids and highlight the importance of these effects in a variety of pathophysiological conditions.

Quantification of calcium signal transmission from sarco-endoplasmic reticulum to the mitochondria

Recent studies have shown that ryanodine and IP3 receptor (RyR/IP3R)-mediated cytosolic Ca2+ signals propagate to the mitochondria, initiating chains of events vital in the regulation of different cellular functions. However, the fraction of released Ca2+ utilized by the mitochondria during these processes has not been quantified. To measure the amount of Ca2+ taken up by the mitochondria, we used a novel approach that involves simultaneous fluorescence imaging of mitochondrial and cytosolic [Ca2+] in permeabilized H9c2 myotubes and RBL-2H3 mast cells. Communication between sarco-endoplasmic reticulum (SR/ER) and mitochondria is maintained in these permeabilized cells, as evidenced by the large RyR/IP3R-driven mitochondrial matrix [Ca2+] and NAD(P)H signals and also by preservation of the morphology of the SR/ER-mitochondrial junctions. Ca2+ was released from the SR/ER by addition of saturating caffeine or IP3 and subsequently thapsigargin (Tg), an inhibitor of SR/ER Ca2+ pumps. The amount of Ca2+ transmitted to the mitochondria was determined by measuring increases of global [Ca2+] in the incubation medium (cytosolic [Ca2+] ([Ca2+]c)). Mitochondrial Ca2+ uptake was calculated from the difference between [Ca2+]c responses recorded in the absence and presence of uncoupler or from [Ca2+]c elevations evoked by uncoupler or ionophore applied after complete Ca2+ mobilization from the SR/ER. [Ca2+]c increases were calibrated by adding Ca2+ pulses to the permeabilized cells. In H9c2 cells, caffeine induced partial mobilization of SR Ca2+ and mitochondria accumulated 26% of the released Ca2+. Sequential application of caffeine and Tg elicited complete discharge of SR Ca2+ without further increase in mitochondrial Ca2+ uptake. In RBL-2H3 mast cells, IP3 by itself elicited complete discharge of the ER Ca2+ store and the increase of the ionophore-releasable mitochondrial Ca2+ content reached 50% of the Ca2+ amount mobilized by IP3 + Tg. Thus, RyR/IP3R direct a substantial fraction of released Ca2+ to the mitochondria.

Selective serotonin-reuptake inhibitor antidepressants increase the risk of falls and hip fractures in elderly people by inhibiting cardiovascular ion channels

Surprising results from recently published retrospective studies show that the use of new selective serotonin-reuptake inhibitor antidepressants (SSRIs), similarly to the older tricyclic antidepressants (TCAs), increases the risk of falls and hip fractures among elderly people.The mechanism whereby antidepressants increase this risk is complex and may include orthostatic hypotension, arrhythmias, sedation and confusion. The increased risk of falls and hip fractures with the use of TCAs is not surprising considering their well-known cardiovascular, anticholinergic and antihistaminergic side-effects. But the increased risk of falls with SSRIs is highly unexpected since these drugs are believed to be free from the disadvantages of TCAs. We hypothesized that the new SSRI antidepressants may also have cardiovascular effects similarly to the older TCA compounds, which may be an explanation for the increased rate of falls and hip fractures. The experimental and clinical evidence in support of this hypothesis are discussed.

Electrophysiological effects of fluoxetine in mammalian cardiac tissues

Fluoxetine is a widely used antidepressant compound having selective serotonin reuptake inhibitor properties. In this study, the actions of fluoxetine were analyzed in guinea pig, rat, rabbit and canine ventricular myocardiac preparations using conventional microelectrode and whole cell voltage clamp techniques. Low concentrations of fluoxetine (1-10 micromol/l) caused significant shortening of action potential duration (APD) and depression of the plateau potential in guinea pig and rabbit papillary muscles and single canine ventricular myocytes. In rat papillary muscle, APD was not affected by fluoxetine (up to 100 micromol/l), however, the drug decreased the force of contraction with EC50 of 10 micromol/l. Fluoxetine (10 micromol/l) also decreased the maximum velocity of depolarization and action potential overshoot in each species studied. At this concentration no effect was observed on the resting membrane potential; high concentration (100 micromol/l), however, caused depolarization. In voltage clamped canine ventricular myocytes, fluoxetine caused concentration-dependent block of the peak Ca2+ current at 0 mV with EC50 of 5.4+/-0.94 micromol/l and Hill coefficient of 1.1+/-0.14 (n=6). In addition, 10 micromol/l fluoxetine shifted the midpoint of the steady-state inactivation curve of the Ca2+ current from -20.7+/-0.65 to -26.7+/-1 mV (P<0.001, n=8) without changing its slope factor. These effects of fluoxetine developed rapidly and were fully reversible. Fluoxetine did not alter voltage-dependence of activation or time constant for inactivation of I(Ca). Fluoxetine had no effect on the amplitude of K+ currents (I(K1) and I(to)). The inhibition of cardiac Ca2+ and Na+ channels by fluoxetine may explain most cardiac side effects observed occasionally with the drug. Our results suggest that fluoxetine may have antiarrhythmic (class I + IV type), as well as proarrhythmic properties (due to impairment of atrioventricular or intraventricular conduction and shortening of repolarization). Therefore, in depressed patients with cardiac disorders, ECG control may be suggested during fluoxetine therapy.

Electrophysiological changes in rat ventricular and atrial myocardium at different stages of experimental diabetes

Action potential configuration in ventricular and atrial myocardium, as well as rate-dependent changes in ventricular action potential duration (APD) were studied and compared in healthy and diabetic rats. Diabetes was induced by a single injection of streptozotocin (STZ, 65 mg kg(-1) i.v.). Conventional microelectrode techniques were applied to record action potentials after the establishment of diabetes (2, 6, 10 and 18 weeks after STZ-treatment). Untreated age-matched animals were used as controls. Both depolarization and repolarization were significantly retarded following STZ-treatment. However, the time course of development of diabetic changes in atrial and ventricular myocardium was different. APD was significantly lengthened from week 2 of diabetes in ventricular, but only from week 6 in atrial preparations. In atrial myocardium, lengthening of APD was more pronounced at early rather than late phases of repolarization. The maximum rate of depolarization (Vmax) was significantly reduced from the 6th week of diabetes in both preparations. No differences were observed in action potential amplitude (except at week 18) and in the resting membrane potential in diabetic rats. Diabetic ventricular preparations showed a positive APD-frequency relationship at any level of repolarization, in contrast to control muscles, where APD25 and APD50 values lengthened. But APD75 and APD90 values were not changed significantly with increase in the pacing frequency. The results indicate that development of diabetic alterations are not fully identical in atrial and ventricular myocardium of the rat, probably owing to differences in density and kinetics of ionic currents responsible for atrial and ventricular action potentials.

Serotonin reuptake inhibitor, fluoxetine, dilates isolated skeletal muscle arterioles. Possible role of altered Ca2+ sensitivity

1. Inhibitors of serotonin reuptake in the central nervous system, such as fluoxetine, may also affect the function of vascular tissues. Thus, we investigated the effect of fluoxetine on the vasomotor responses of isolated, pressurized arterioles of rat gracilis muscle (98 +/- 4 microns in diameter at 80 mmHg perfusion pressure). 2. We have found that increasing concentrations of fluoxetine dilated arterioles up to 155 +/- 5 microns with an EC50 of 2.5 +/- 0.5 x 10(-6) M. 3. Removal of the endothelium, application of 4-aminopyridine (4-AP, an inhibitor of aminopyridine sensitive K+ channels), or use of glibenclamide (an inhibitor of ATP-sensitive K+ channels) did not affect the vasodilator response to fluoxetine. 4. In the presence of 10(-6), 2 x 10(-6) or 10(-5) M fluoxetine noradrenaline (NA, 10(-9)-10(-5) M) and 5-hydroxytryptamine (5-HT, 10(-9)-10(-5)M)-induced constrictions were significantly attenuated resulting in concentration-dependent parallel rightward shifts of their dose-response curves (pA2 = 6.1 +/- 0.1 and 6.9 +/- 0.1, respectively). 5. Increasing concentrations of Ca2+ (10(-4) 3 x 10(-2) M) elicited arteriolar constrictions (up to approximately 30%), which were markedly reduced by 2 x 10(-6)M fluoxetine, whereas 10(-5)M fluoxetine practically abolished these responses. 6. In conclusion, fluoxetine, elicits substantial dilations of isolated skeletal muscle arterioles, a response which is not mediated by 4-AP- and ATP-sensitive K+ channels or endothelium-derived dilator factors. The findings that fluoxetine had a greater inhibitory effect on Ca2+ elicited constrictions than on responses to NA and 5-HT suggest that fluoxetine may inhibit Ca2+ channel(s) or interfere with the signal transduction by Ca2+ in the vascular smooth muscle cells.

Mitochondrial ca(2+) signaling and cardiac apoptosis

The broad significance of apoptosis in the cardiovascular system only began to be recognized more widely recently. Apoptotic cell death is a normal component of postnatal morphogenesis of the human cardiac conduction system and may also be involved in the pathogenesis of a variety of cardiovascular diseases, including heart failure, myocardial infarction and atherosclerosis. Recently, it has become evident that mitochondria play important role in the signaling machinery of apoptotic cell death by releasing several apoptotic factors such as cytochrome c, apoptosis-inducing factor and procaspases. Furthermore, calcium signals have been identified as one of the major signals that converge on mitochondria to trigger the mitochondrion-dependent pathway of the apoptotic cell death. Calcium signals are also important in the physiological control of mitochondrial energy metabolism and it has not yet been explored how Ca(2+) turns from a signal for life to a signal for death. Since large elevations of cytosolic [Ca(2+)] ([Ca(2+)](c)) occur during each heartbeat in cardiac myocytes and these [Ca(2+)](c) signals may efficiently propagate to the mitochondria, the Ca(2+)-dependent mitochondrial pathways of apoptosis can be particularly important in the heart. This review is concerned with the role of mitochondrial Ca(2+) signaling in the control of cardiac apoptosis.

Cardiac electrophysiological effects of citalopram in guinea pig papillary muscle comparison with clomipramine

The effect of citalopram, a selective serotonin reuptake inhibitor (SSRI) antidepressant, was studied on cardiac action potential configuration and compared with that of the tricyclic antidepressant (TCA) clomipramine. Conventional microelectrode techniques were used in right ventricular papillary muscle preparations of the guinea pig. Citalopram caused a concentration-dependent (10-100 microM) shortening of action potential duration (APD), depression of plateau and overshoot potential, and reduction of maximum velocity of depolarization (V(max)). No significant changes in resting membrane potential were observed. Similar results were obtained with clomipramine; however, reduction of V(max) and overshoot was more pronounced with clomipramine, whereas citalopram caused relatively greater shortening of APD. Effects of both drugs were partly reversible. The results indicate that the SSRI antidepressant citalopram, similarly to TCA compounds, alters cardiac action potential configuration in guinea pig ventricular muscle, probably owing to inhibition of cardiac Na(+) and Ca(2+) channels. Differences in cardiac side effects of the two drugs may be related to their different actions on cardiac action potential configuration.

Topical administration of a novel nitric oxide donor, linear polyethylenimine-nitric oxide/nucleophile adduct (DS1), selectively increases vaginal blood flow in anesthetized rats

The aim of the present study was to test the effects of a topical administration of a novel nitric oxide donor, linear polyethylenimine-nitric oxide/nucleophile adduct (DS1), on vaginal blood flow and hemodynamics in rats. Laser Doppler flowmetry was used to measure blood flow changes following topical application of DS1 (0.3 or 1.5 mg in 0.15 ml saline) into the vagina of anesthetized Wistar rats. In vivo hemodynamic parameters were measured with Millar-tip-catheter placed in the left ventricle. DS1 (1.5 mg) increased vaginal blood flow by 191+/-24, 226+/-22 and 166+/-23% of the baseline value (at 5, 15 and 30 min, respectively, after application) without affecting systemic blood pressure, heart rate and cardiac function. The increased vaginal blood flow following DS1 application returned to baseline between 45 and 60 min. Thus, topical application of nitric oxide donors such as DS1 may be useful for the treatment of female sexual dysfunction that develops due to an impairment of local blood flow supply to the vaginal tissue.

Serotonin reuptake inhibitors fluoxetine and citalopram relax intestinal smooth muscle

Selective serotonin reuptake inhibitor antidepressants (SSRIs) exert depressant effects on cardiac myocytes and vascular smooth muscle cells by inhibiting Ca2+ channels. We hypothesized that the SSRIs fluoxetine and citalopram affect the contractile activity of intestinal smooth muscle by interfering with Ca2+ entry and (or) signaling pathways. The effects of fluoxetine and citalopram on contractions of guinea-pig ileum longitudinal muscle-myenteric plexus preparations (LMMP) were compared with the effects of the voltage-operated Ca2+ channel inhibitors nifedipine and diltiazem. In a concentration-dependent manner, nifedipine, diltiazem, fluoxetine, and citalopram elicited relaxation of LMMPs contracted by electrical field stimulation (EC50 values of 4 x 10(-7) M, 1.4 x 10(-6) M, 1.4 x 10(-5), and 6.8 x 10(-6) M, respectively). Nifedipine, diltiazem, fluoxetine, and citalopram also relaxed LMMPs contracted with a depolarizing concentration of KCl (48 mM; EC50 values of 1.8 x 10(-8) M, 1.4 x 10(-7) M, 3.7 x 10(-6) M, and 6.3 x 10(-6), respectively), a response that could be reversed by increasing the extracellular Ca2+ concentration (2.5-30 mM). These data suggest that fluoxetine and citalopram elicit relaxation of intestinal smooth muscle, likely by inhibiting Ca2+ channel(s). This effect may be of clinical importance.

Activation of poly(ADP-ribose) polymerase contributes to the endothelial dysfunction associated with hypertension and aging

Increased production of reactive oxygen and nitrogen species has recently been implicated in the pathogenesis of endothelial dysfunction associated with atherosclerosis, hypertension and aging. Oxidant induced cell injury triggers the activation of nuclear enzyme poly(ADP-ribose) polymerase (PARP), which in turn contributes to cardiac and vascular dysfunction in various pathophysiological conditions including diabetes, reperfusion injury and circulatory shock. Here we investigated the role of PARP activation in the pathogenesis of cardiac and endothelial dysfunction associated with atherosclerosis, hypertension and aging. Retired breeder spontaneously hypertensive rats (SHR, 40 weeks old) and apolipoprotein E knockout mice (apoE-Ko, 10 weeks old) were treated for 20 weeks with vehicle or the potent PARP inhibitor PJ34. In the vehicle-treated SHR rats and apoE-Ko mice (kept on atherogenic diet) there was a significant loss of endothelial function, as measured by the relaxant responsiveness of vascular rings to acetylcholine. SHR rats also developed severe hypertension and cardiac hypertrophy. Treatment with the PARP inhibitor did not influence high blood pressure and cardiac hypertrophy in SHR rats, but it improved Ach-induced, NO-mediated vascular relaxation. In addition to the beneficial effects of chronic treatment with PARP inhibitor, 1-h in vitro incubation of aortic rings from SHR rats with PJ34 (3 micromol/l) was also able to improve the endothelial dysfunction. In contrast, in apoE-Ko mice PJ34 treatment did not affect the parameters studied. Thus, PARP activation contributes to the pathogenesis of endothelial dysfunction associated with hypertension and aging, but not in the current experimental model of atherosclerosis.

Electrophysiological effects of homocysteine in isolated rat right ventricular papillary muscles and left atria

There is clinical and epidemiological evidence that elevated plasma homocysteine (Hcy) levels are associated with increased myocardial infarction mortality; however, very little is known about Hcy's direct cardiac effects. Thus, we aimed to characterize the cellular electrophysiologic effects of Hcy, a sulfur-containing amino acid in isolated rat hearts. A conventional microelectrode technique was used in left atria and right ventricular papillary muscles. At concentrations higher than 10(6) M, Hcy significantly decreased the maximum rate of rise of the depolarization phase (Vmax) in both cardiac preparations in a dose-dependent manner. Hcy at 10(-4)-5 x 10(-4) M concentrations increased the action potential duration (APD) at late stages of repolarization (at 75% and 90% of APD) both in atria and in ventricles. There was a slight decrease in action potential amplitude in ventricular papillary muscles and atria at concentrations higher that 10(-5) M. The resting membrane potential and the early repolarization phase (APD25 and APD50) remained unchanged in every preparation studied at all concentrations of Hcy administered. The present data suggest that homocysteine may decrease the Na+ channel activity in in vitro cardiac preparations. reserved.

Review of cardiovascular effects of fluoxetine, a selective serotonin reuptake inhibitor, compared to tricyclic antidepressants

Fluoxetine is an antidepressant drug, a potent and specific inhibitor of serotonin reuptake (SSRI). Evidence suggests that being compared with tricyclic antidepressants, fluoxetine may cause significantly fewer anticholinergic, antihistaminergic and cardiotoxic side effects in the treatment of major depressive disorders. Chronic treatment with fluoxetine was not reported to affect the electrocardiogram (ECG). There is no clinical evidence of conduction delay and very little evidence of orthostatic hypotension. In the overdosed patients fewer cardiac symptoms were reported than with tricyclic antidepressants. However, dysrhythmia (atrial fibrillation and bradycardia) and syncope associated with fluoxetine treatment and overdose were reported. Although such reports have not been common, they do raise concerns. Thus we investigated the direct cardiovascular effects of the fluoxetine in isolated heart preparations and vessels of rats and rabbits. From 10(-6)M to 10(-4)M concentrations fluoxetine showed cardiodepressant and vasodilatory effects. These effects were similar to those of previously reported on tricyclic compounds. This review is a brief summary of possible cardiovascular effects of fluoxetine and other new SSRIs antidepressants from the literature based on experience of clinical studies and our experiments with fluoxetine on isolated rat and rabbit cardiac preparations and vessels. Possible explanations of the lower incidence of cardiovascular complications with fluoxetine in humans and cardiodepressant effects in vitro are discussed.

Post-partum prolongation of the atrial repolarization in rabbit

Female sexual steroids are known to modify the expression of various K+ channels and thus they can alter cardiac repolarization. In the present work, using conventional microelectrode techniques, action potential characteristics were studied in atrial myocardium isolated from virgin, late pregnant, early (1-3 days) post-partum and late (2-3 weeks) post-partum rabbits. No changes in action potential configuration were observed during pregnancy. However, the duration, overshoot and amplitude of action potentials were significantly increased in the early (1-3 days) post-partum period. Resting potential and maximum rate of depolarization remained unchanged. The observed changes were transient, normal action potential characteristics were obtained at weeks 2-3 post-partum. 4-aminopyridine (1 mmol L(-1)). caused a marked lengthening of action potential duration in all preparations obtained from non-pregnant and pregnant rabbits, whereas this 4-aminopyridine-induced prolongation was moderate in those preparations excised from the hearts of early post-partum animals. Action potential configuration was not affected by pinacidil (10 micromol L(-1)) or glibenclamide (5 micromol L(-1)) in non-pregnant or pregnant animals. In preparations obtained from early post-partum rabbits, pinacidil significantly shortened action potential duration, which was reverted by glibenclamide. The lengthening of action potential duration together with the decreased sensitivity to 4-aminopyridine observed in early post-partum animals may probably be caused by reduction of the transient outward K+ current at this stage. The results also suggest that electrophysiological alterations in the early post-partum period may probably be more pronounced than those associated with pregnancy itself.