Showing papers in "Journal of Cardiovascular Pharmacology in 2003"

Efficacy and safety of treprostinil: an epoprostenol analog for primary pulmonary hypertension.

Abstract: Intravenous epoprostenol is currently FDA approved for management of primary pulmonary hypertension, but it requires intravenous infusion and is associated with adverse effects. The objective of this study was to evaluate the effects of an epoprostenol analog, treprostinil, for management of pulmonary hypertension. Ten tertiary care academic institutions with pulmonary hypertension programs participated in these pilot trials. In the first trial, intravenous epoprostenol and intravenous treprostinil were compared. In the second trial, intravenous treprostinil and subcutaneous treprostinil were compared. In the third trial, subcutaneous treprostinil was compared with placebo infusion during an 8-week period. Intravenous epoprostenol and intravenous treprostinil resulted in a similar reduction in pulmonary vascular resistance acutely (22% and 20%, respectively). Intravenous treprostinil and subcutaneous treprostinil also demonstrated comparable short-term decrease in pulmonary vascular resistance (23% and 28%, respectively). The placebo-controlled 8-week trial demonstrated a mean improvement of 37 +/- 17 m as measured by the 6-minute walk distance in patients receiving treprostinil compared with a 6 +/- 28 m reduction in those receiving placebo. There were trends toward an improvement in cardiac index and pulmonary vascular resistance index in the treprostinil group. Subcutaneous treprostinil has favorable hemodynamic effects when given acutely and in the short term. Treprostinil can be given safely to an ambulatory patient with a novel subcutaneous delivery pump system.

Cannabinoids acting on CB1 receptors decrease contractile performance in human atrial muscle.

Abstract: Cannabinoids elicit hypotension mainly via activated CB(1) receptors and show complex cardiovascular actions Effects on human heart muscle have not been studied yet Isolated human atrial heart muscle preparations were stimulated by electrical field with 1 Hz to contract isometrically at optimal length and were challenged with the endogenous cannabinoid arachidonyl ethanolamide (anandamide), the metabolically stable analogue R-methanandamide, and the potent synthetic CB(1) receptor agonist HU-210 Anandamide dose-dependently decreased systolic force (822 +/- 48% and 608 +/- 68% of maximal systolic force for 01 and 1 microM, respectively, P < 005) The selective CB(1) receptor antagonist AM-251 (1 microM, P < 005), but not the CB(2) receptor antagonist, AM-630 (1 microM), the nitric oxide synthase inhibitor N omega-nitro-l-arginine methyl ester (l-NAME) (500 microM), or the cyclooxygenase inhibitor indomethacin (100 microM), prevented the effect Contrary to indomethacin, l-NAME alone showed negative inotropic effects (721 +/- 354%, P < 0001) The R-methanandamide (1 microM: 504 +/- 35%, P < 0001) and HU-210 (1 microM: 601 +/- 38%, P < 0001) had similar negative inotropic effects The existence of CB(1) receptors on heart muscle was verified using Western blot analysis and immunofluorescence staining The conclusion is that anandamide, R-methanandamide, and HU-210 decrease contractile performance in human atrial muscle via CB(1) receptors

Estrogen attenuates the emotional stress-induced cardiac responses in the animal model of Tako-tsubo (Ampulla) cardiomyopathy.

Abstract: Reduction of estrogen levels may underlie the high incidence of 'Tako-tsubo (Ampulla) cardiomyopathy in postmenopausal females. Ovariectomized (OVX) and estradiol-supplemented ovariectomized female rats (OVX + E) were subjected to immobilization stress, an animal model of Tako-tsubo cardiomyopathy. In order to evaluate cardiac changes, left ventriculography and electrocardiography were performed under anesthesia (control). Next day, the conscious rats were exposed to immobilization stress, and left ventriculography was performed (stress). In OVX rats, percentage contraction in left ventriculography was significantly reduced in response to stress, while it was not significantly changed in OVX + E rats. In both groups, heart rate was significantly increased in response to stress. However, heart rate in stress was significantly higher in OVX than in OVX + E rats. In summary, these data suggest that increase of serum estradiol levels can diminish the pathological changes in the heart induced by emotional stress.

Blinded test in isolated female rabbit heart reliably identifies action potential duration prolongation and proarrhythmic drugs: importance of triangulation, reverse use dependence, and instability.

Abstract: Drug-induced proarrhythmia is a rare but potentially lethal adverse drug reaction. To test whether the SCREENIT system (an automated computerized test apparatus), using an isolated perfused heart obtained from female rabbits, could correctly identify agents that lengthen the action potential duration (APD) and drugs known to induce proarrhythmia, 14 drugs (penicillin G, haloperidol, adriamycin, indapamide, verapamil, aspirin, lidocaine, clomipramine, propranolol, erythromycin, quinidine, terfenadine, amiodarone, and thioridazine) were coded and submitted for a blinded test. Of these drugs, eight are reported to induce QT prolongation in the clinic (adriamycin, clomipramine, quinidine, amiodarone, and thioridazine), while three do not lengthen and three shorten the QT. To test for reproducibility, four drugs were given in duplicate (haloperidol, aspirin, erythromycin, and terfenadine). The drug effects on monophasic APD, conduction, instability (index of variability of APD), triangulation (index of duration of fast repolarization), and reverse use dependence were measured at five drug concentrations (0.05, 0.15, 0.5, 1.5, and 5 mg/l). All 14 blinded drugs, in the concentrations used, were correctly identified as to their effects on APD and conduction. The drugs eliciting drug-induced proarrhythmia in patients were also identified as promoting instability, triangulation, and reverse use dependence in the rabbit heart. Importantly, none of the safe agents was labeled as proarrhythmic, and the results were very consistent between duplications. In conclusion, SCREENIT correctly identifies prolongation of APD, accurately separates safe agents form proarrhythmic drugs, and has highly reproducible results. Thus, the isolated perfused rabbit heart can be a valuable tool in a preclinical proarrhythmia test battery in drug development.

Electrophysiologic characterization of dronedarone in guinea pig ventricular cells.

Abstract: The electrophysiological properties of dronedarone (SR33589), a noniodinated amiodarone-like agent, were studied on action potential (AP) and contraction of papillary muscle and on membrane ionic currents, Ca2+ transient, and shortening of ventricular cells of the guinea pig heart. In multicellular preparations, dronedarone (3, 10, and 30 microM) decreased maximum rate of rise of AP (dV/dt max) with a concentration- and frequency-dependent relationship; resting potential was not modified and AP amplitude was decreased only at 30 microM. The effects of dronedarone on AP durations (APDs) at different percentages of repolarization were not significantly changed, except for a slight decrease in APD30 and APD50 at the highest concentration. In isolated ventricular myocytes, dronedarone inhibited rapidly activating delayed-rectifier K+ current (I(Kr)) (median inhibitory concentration [IC50] /= 30 microM). Dronedarone blocked L-type Ca2+ current (I(Ca(L))) (IC50 = 0.18 +/- 0.018 microM at a stimulation frequency of 0.033 Hz) in a use- and frequency-dependent manner. Simultaneously to these electrophysiological effects, dronedarone reduced contraction amplitudes of papillary muscle and decreased Ca2+ transient and shortening of ventricular myocytes. The results show that dronedarone is a multichannel blocker because it decreases dV/dt max (I(Na)), I(Ca(L)), I(Kr), I(Ks), and I(K1). These effects are accompanied by a reduction in free intracellular calcium and contraction amplitudes. Dronedarone does not significantly change APD whatever the stimulation frequency. Our data demonstrate that the acute electrophysiological characteristics of dronedarone, despite absence of iodine in its molecular structure, are very similar to those of amiodarone in cardiac ventricle.

Effect of eplerenone, a selective aldosterone blocker, on blood pressure, serum and macrophage oxidative stress, and atherosclerosis in apolipoprotein E-deficient mice.

Abstract: Oxidative stress is involved in the pathogenesis of atherosclerosis, and angiotensin II (AT-II) induces oxidative stress and enhances atherogenesis. Aldosterone, which has an important role in the pathology of heart failure, has recently been implicated as a mediator of AT-II biologic activities. In this study, we analyzed whether administration of the selective aldosterone blocker eplerenone to atherosclerotic apolipoprotein E-deficient (E0) mice would affect their oxidative status and atherogenesis. Apolipoprotein E-deficient mice were administered chow containing eplerenone (200 mg/kg/day) for 3 months. Blood pressure, serum and macrophage oxidative status, and aortic atherosclerotic lesion area were evaluated in mice treated with eplerenone compared with untreated mice. Eplerenone administration significantly decreased systolic and diastolic blood pressure by 12% and 11%, respectively, compared with untreated mice. Serum susceptibility to lipid peroxidation decreased by as much as 26%, and serum paraoxonase activity increased by 28% in eplerenone-treated mice compared with untreated mice. Peritoneal macrophages from eplerenone-treated mice contained reduced levels of lipid peroxides, and their macrophage oxidation of low-density lipoprotein (LDL) and superoxide ion release were significantly reduced (by 17% and 43%, respectively), compared to untreated mice. Daily injections of AT-II (0.1 mL, 10(-)7M) during the final 3 weeks of the study in eplerenone-treated mice substantially attenuated the eplerenone-mediated reduction in macrophage superoxide release and LDL oxidation. Finally, the atherosclerotic lesion area in aortas of eplerenone-treated mice was significantly reduced (by 35%) versus untreated mice, and this effect was reversed by AT-II. Administration of the selective aldosterone blocker eplerenone significantly reduced oxidative stress and atherosclerosis progression in E0 mice. These data suggest that aldosterone could have a significant pro-oxidative role in the pathogenesis of atherosclerosis.

Cardiovascular effects of acute oxygen administration in healthy adults.

Abstract: :Supplementary oxygen is commonly administered in current medical practice. However, attention has recently been drawn to the potentially disadvantageous hemodynamic consequences in certain patients. Possible mechanisms underlying the cardiovascular responses to acute hyperoxia are unclear.

Abciximab, eptifibatide, and tirofiban exhibit dose-dependent potencies to dissolve platelet aggregates.

Abstract: Platelet GPIIb/IIIa antagonists are not only used to prevent platelet aggregation, but also in combination with thrombolytic agents for the treatment of coronary thrombi. Recent data indicate a potential of abciximab alone to dissolve thrombi in vivo. We investigated the potential of abciximab, eptifibatide, and tirofiban to dissolve platelet aggregates in vitro. Adenosine diphosphate (ADP)-induced platelet aggregation could be reversed in a concentration-dependent manner by all three GPIIb/IIIa antagonists when added after the aggregation curve reached half-maximal aggregation. The concentrations chosen are comparable with in vivo plasma concentrations in clinical applications. Disaggregation reached a maximum degree of 72.4% using 0.5 microg/ml tirofiban, 91.5% using 3.75 microg/ml eptifibatide, and 48.4% using 50 microg/ml abciximab (P < 0.05, respectively). A potential fibrinolytic activity of the GPIIb/IIIa antagonists was ruled out by preincubation with aprotinin or by a plasma clot assay. A stable model Chinese hamster ovary (CHO) cell line expressing the activated form of GPIIb/IIIa was used to confirm the disaggregation capacity of GPIIb/IIIa antagonists found in platelets. Not only abciximab, but also eptifibatide and tirofiban have the potential to disaggregate newly formed platelet clusters in vitro. Because enzyme-dependent fibrinolysis does not appear to be involved, competitive removal of fibrinogen by the receptor antagonists is the most likely mechanism.

Acute reduction of myocardial infarct size by a hydroxymethyl glutaryl coenzyme A reductase inhibitor is mediated by endothelial nitric oxide synthase.

Abstract: In addition to their lipid-lowering properties, statins improve endothelial function by increasing the activity of endothelial nitric oxide synthase (eNOS). It was hypothesized that, by this mechanism, statins protect the myocardium from ischemia/reperfusion injury in normocholesterolemic animals. Rats were pretreated for 1 week with either cerivastatin (0.3 mg/kg/d) or placebo. Anesthetized animals underwent 30 minutes of coronary artery occlusion (CAO) followed by 180 minutes of reperfusion. In a separate set of experiments, the NOS inhibitor L-NAME (15 mg/kg; N ω -nitro-L-arginine methyl ester) was administered 15 minutes before CAO. Cerivastatin decreased infarct size by 49% (P < 0.05) without reducing plasma cholesterol levels. Cerivastatin increased myocardial eNOS mRNA and NOS activity and by 52% and 58% (P < 0.05), respectively. Cardioprotection and upregulation of eNOS activity evoked by cerivastatin were not observed in rats cotreated with L-NAME. These results show that statins reduce the extent of myocardial necrosis in normocholesterolemic rats after acute ischemia/reperfusion injury by increasing myocardial eNOS activity. Therefore, statins may protect the heart not only by reducing the incidence of ischemic events, but also by limiting cell damage during acute myocardial infarction.

HMR 1556, a potent and selective blocker of slowly activating delayed rectifier potassium current.

Abstract: The slowly activating delayed rectifier potassium current (IKs) contributes prominently to ventricular repolarization of the cardiac action potential. Development of a selective IKs blocker is important for the elucidation of the physiologic and pathophysiologic relevance of IKs and the development of antiarrhythmic strategies. HMR 1556 [(3R,4S)-(+)-N-[3-hydroxy-2,2-dimethyl-6-(4,4,4-trifluorobutoxy) chroman-4-yl]-N-methylmethanesulfonamide] is a new chromanol derivative developed as a selective IKs blocker. Chromanol 293B, the most specific IKs blocker currently available, also inhibits the transient outward current (Ito). HMR 1556 was examined for its effects on IKs compared with rapidly activating delayed rectifier (IKr), inward rectifier (IK1), Ito, and L-type calcium (ICa.L) currents in canine left ventricular myocytes. HMR 1556 (0.5-500 nM ) inhibited IKs in a concentration-dependent manner (IC50 of 10.5 nM, compared with chromanol 293B's IC50 of 1.8microM). Inhibition of Ito was observed only at relatively high concentrations (IC50 of 33.9 microM comparable to chromanol 293B's IC of 38 microM). High concentrations of HMR 1556 also inhibited ICa.L (IC of 27.5 microM) and IKr (IC50 of 12.6 microM) while IK1 was unaffected. Our results indicate that HMR 1556 is superior to chromanol 293B in its potency and specificity for inhibition of IKs, making it a valuable experimental tool and a potential therapeutic agent.

Effect of allopurinol pretreatment on free radical generation after primary coronary angioplasty for acute myocardial infarction

Abstract: Allopurinol, an inhibitor of xanthine oxidase, was shown to improve the regional ventricular function after coronary artery occlusion and reperfusion in animal models. The effects of oral administration of allopurinol on a transient increase in free radical generation after primary percutaneous transluminal coronary angioplasty (PTCA) in patients with acute myocardial infarction (AMI) and on their clinical outcomes were examined. Thirty-eight AMI patients undergoing primary PTCA were randomly assigned to control (group 1, n = 20) and allopurinol treatment groups (group 2, n = 18). Allopurinol (400 mg) was administered orally just after the admission (approximately 60 min before reperfusion). Free radical production was assessed by successive measurement of urinary excretion of 8-epi-prostaglandin F(2alpha) (PGF(2alpha)) after PTCA. Urinary 8-epi-PGF(2alpha) excretion was increased by twofold at 60-90 min after PTCA compared with the baseline value in group 1. This increase was completely inhibited in group 2. Plasma allopurinol concentration was 1,146 +/- 55 ng/ml in group 2 when reperfusion was achieved. Slow flow in the recanalized coronary artery after PTCA occurred less frequently in group 2 than in group 1. Cardiac index determined just after reperfusion and left ventricular ejection fraction at 6 months after PTCA were both significantly greater in group 2 than in group 1 although pulmonary capillary wedge pressure was similar in the two groups. In conclusion, allopurinol pretreatment is effective in inhibiting generation of oxygen-derived radicals during reperfusion therapy and the recovery of left ventricular function in humans.

Involvement of the β3 adrenoceptor in nebivolol-induced vasorelaxation in the rat aorta

Abstract: Nebivolol is a highly selective beta(1) adrenoceptor blocker with additional vasodilating properties. Although it has been shown that the nebivolol-induced vasorelaxation is nitric oxide (NO) and cGMP dependent, the receptor that mediates these actions remains controversial, and serotonergic as well as beta-adrenergic pathways may be involved. Therefore, functional experiments investigating the receptor involved in nebivolol-induced vasorelaxation were performed in the rat aorta. Isolated aortic rings were exposed to cumulative concentrations of nebivolol. Nebivolol concentrations of 3 micromol/L and higher caused vasorelaxation, which was inhibited by the presence of the NO synthase inhibitor l-NNA (100 micromol/L), or by mechanical removal of the endothelium. Exposure of the vessel rings to the selective 5-HT(1A) antagonist NAN-190 (1 micromol/L) or the 5-HT(1/2) antagonist methysergide (1 micromol/L) did not influence nebivolol-induced vasorelaxation. Similarly, the incubation with the beta(2)-adrenoceptor antagonist butoxamine (50 micromol/L) did not prevent vasorelaxation. The selective beta(3)-adrenoceptor antagonist S-(-)-cyanopindolol (1 micromol/L), however, significantly counteracted the nebivolol-induced vasorelaxation. Furthermore, exposure of the aortic rings to cumulative concentrations of the beta(3) selective adrenoceptor agonist BRL37344 caused, like nebivolol, NO-dependent vasorelaxation that was antagonized by S-(-)-cyanopindolol. The results suggest that nebivolol-induced NO-dependent vasorelaxation is, at least in part, caused by a beta(3)-adrenoceptor agonistic effect.

Implications of oxidative stress and homocysteine in the pathophysiology of essential hypertension

Abstract: The present review examines the clinical and experimental data to support the view that homocysteine and oxidative stress, two alternative risk factors of vascular disease, may play a role in the pathogenesis of primary or essential hypertension. Although the precise mechanism of this disease has not been elucidated, it may be related to impairment of vascular endothelial and smooth muscle cell function. Thus, the occurrence of endothelial dysfunction could contribute to alterations of the endothelium-dependent vasomotor regulation. Hyperhomocysteinemia limits the bioavailability of nitric oxide, increases oxidative stress, stimulates the proliferation of vascular smooth muscle cells, and alters the elastic properties of the vascular wall. The link between oxidative stress and hyperhomocysteinemia is also biologically plausible, because homocysteine promotes oxidant injury to the endothelium. Cumulated evidence suggests that the diminution of oxidative stress with antioxidants or the correction of hyperhomocysteinemia with vitamins-B plus folic acid, could be useful as an adjuvant therapy for essential hypertension. Further studies involving long-term trials could help to assess the tolerability and efficacy of the use of these therapeutic agents.

Abnormal nocturnal blood pressure falls in elderly hypertension: clinical significance and determinants.

Abstract: Abnormal patterns of diurnal blood pressure variation have been reported to be related to advanced target organ damage and poor cardiovascular prognosis. We studied silent cerebrovascular disease and stroke events in older Japanese patients with different nocturnal blood pressure dipping. There was a J-shaped relationship of nocturnal dipping status with silent cerebral infarcts detected by brain magnetic resonance imaging at baseline, and with stroke incidence during the follow-up period. The extreme-dippers (with marked nocturnal blood pressure dipping) and the risers (with higher nocturnal blood pressure than awake blood pressure) had a higher prevalence of silent cerebral infarcts and a poorer stroke prognosis than those with appropriate nocturnal blood pressure dipping (dippers). The extreme-dippers tended to have predominant systolic hypertension and increased blood pressure variability. Several factors affect the diurnal blood pressure variation pattern. The non-dipping pattern is associated with autonomic nervous dysfunction and poor sleep quality due to nocturnal behavior and sleep apnea. The extreme-dippers might have increased arterial stiffness with reduced circulating blood volume in addition to an excessive morning surge due to alpha-adrenergic hyperactivity. Anti-hypertensive medication that normalizes the diurnal blood pressure variation might improve the cardiovascular prognosis in high-risk hypertensive patients.

Effect of high-dose statin treatment on plasma concentrations of endogenous nitric oxide synthase inhibitors.

Abstract: Asymmetric dimethylarginine (ADMA) and monomethylarginine (LMMA) are endogenous inhibitors of nitric oxide synthase. A high level of ADMA in plasma has shown to be a significant risk factor for acute coronary syndromes and elevated plasma ADMA levels are prevalent in patients with hypercholesterolemia. It was therefore hypothesized that lowering plasma cholesterol levels with statin treatment would also lower ADMA concentrations. This double-blind study addressed the effect of high-dose statin treatment on plasma levels of ADMA and LMMA. Forty-eight subjects with mild hypercholesterolemia were randomly assigned to receive simvastatin 80 mg/d, atorvastatin 40 mg/d, or placebo for 8 weeks. Both statins decreased low-density lipoprotein cholesterol effectively (simvastatin 54% and atorvastatin 49%). However, concentrations of arginine derivatives remained unchanged during statin treatment and did not correlate with cholesterol levels. This study indicates that statin treatment has no clear influence on plasma ADMA or LMMA concentrations.

Molecular mechanism of emotional stress-induced and catecholamine-induced heart attack.

Abstract: Emotional or physical stress triggers 'tako-tsubo' cardiomyopathy or 'transient left ventricular apical ballooning', but the pathogenesis is unclear. In response to the immobilization stress of rats, a useful model of emotional stress, rapid activation of p44/p42 mitogen-activated protein kinase was observed in the heart, followed by a transient upregulation of immediate early genes in the smooth muscle cells of coronary arteries, the endothelial cells and the myocardium. Heat shock protein 70 was induced in the aortic and coronary arterial smooth muscle cells and in the myocardium. Natriuretic peptide genes were also upregulated in the myocardium. Sequential gene expression can be considered as an adaptive response to emotional stress. Blocking of both alpha-adrenoceptors and beta-adrenoceptors eliminated the upregulation of immediate early genes induced by stress, while alpha-agonists and beta-agonists upregulated immediate early genes in the perfused heart. Activation of alpha-adrenoceptors and beta-adrenoceptors is the primary trigger of emotional stress-induced molecular changes in the heart.

Anti-Ischemic Effects of Ivabradine, a Selective Heart Rate-Reducing Agent, in Exercise-Induced Myocardial Ischemia in Pigs

Abstract: The effects of ivabradine, a novel heart rate-reducing agent that inhibits the cardiac pacemaker current If, were compared with those of the beta-adrenergic blocker propranolol, in a model of exercise-induced regional myocardial ischemia in pigs. Five Yucatan micropigs were chronically instrumented to measure hemodynamics, regional myocardial contractility, and local electrograms, and a fixed stenosis of the left anterior descending coronary artery was induced using a clip. Each animal underwent three experiments on different days, each consisting of two treadmill exercise sessions, 4 hours apart. Ivabradine 5 mg/kg, propranolol 5 mg/kg, or vehicle was administered orally 3 hours before the second exercise session. Exercises before treatment and after vehicle produced reproducible hemodynamic changes and regional myocardial ischemia in the area perfused by the stenosed coronary artery, indicated by ST segment shift and regional contractile dysfunction. Ivabradine and propranolol were equipotent in reducing heart rate at rest and limiting tachycardia during exercise. Ivabradine, unlike propranolol, did not reduce left ventricular contractility at rest or during exercise, and did not increase atrio-ventricular conduction time. Both compounds reduced the exercise-induced ST segment shift in the ischemic region by approximately 80%, but ivabradine preserved systolic shortening to a significantly greater degree than propranolol (P < 0.05).

Central nervous system blockade by peripheral administration of AT1 receptor blockers.

Abstract: After peripheral administration, AT1 receptor blockers appear to be able to enter the brain and cause AT1 receptor blockade in the central nervous system. In the current study, we investigated the effects of subcutaneous administration of embusartan versus losartan on inhibition of AT1 receptor binding in rat brain by in vitro autoradiography. At 4 hours after single doses of 5, 30, or 100 mg/kg, both losartan and embusartan decreased iodine 125I Ang II binding dose dependently in brain structures that express AT1 receptors both outside (e.g., organum vasculosum laminae terminalis) and within (e.g., paraventricular nucleus) the blood–brain barrier. At low doses, embusartan was twofold more potent than losartan inside but not outside the blood–brain barrier. After chronic treatment (30 mg/kg daily for 6 days), at 4 hours after the last dose, embusartan still caused more inhibition than losartan in the brain structures inside the blood–brain barrier. At 24 hours after the last dose, a modest, better inhibition for embusartan versus losartan remained: from 15% to 33% versus 10% to 24%, respectively. At 36 hours after the last dose, the inhibition for both blockers had almost completely disappeared inside the blood–brain barrier but persisted in, for example, the kidneys. These results demonstrate that—likely because of its high lipophilic character—embusartan appears to penetrate the blood–brain barrier more easily than losartan and therefore causes more effective AT1 receptor blockade in nuclei within the blood–brain barrier.

Positive inotropic effect of ouabain on isolated heart is accompanied by activation of signal pathways that link Na+/K+-ATPase to ERK1/2.

Abstract: Exposure of cultured rat cardiac myocytes to ouabain is known to cause the interaction of Na+/K+-ATPase with adjacent proteins, leading to activation of multiple signal transduction pathways, regulation of growth-related genes, and hypertrophy. The aim of this work was to determine if the proximal signaling events identified in cultured myocytes also occur in isolated intact hearts of rat and guinea pig in response to positive inotropic doses of ouabain. Langendorff rat heart preparations were exposed to 50 microM ouabain to produce positive inotropy without toxicity, and assayed for Src kinase, protein kinase C, and extracellular signal-regulated kinases 1 and 2 (ERK(1/2)). These kinases were rapidly activated by ouabain as in cultured cells. In isolated guinea pig hearts, 1 microM ouabain caused ERK(1/2) activation comparable to the effect of 50 microM ouabain in rat heart and consistent with the higher ouabain sensitivity of the contractility of guinea pig heart. These data show that the proximal ouabain-induced signal pathways previously noted in cultured cells are not artifacts of dispersion/culturing of myocytes, and are not the peculiar properties of the rat heart with its relatively low ouabain sensitivity. They also suggest that treatment with positive inotropic doses of cardiac glycosides is likely to be associated with changes in the cardiac phenotype.

Adenosine Receptor Subtypes Mediating Coronary Vasodilation in Rat Hearts

Abstract: Adenosine receptor-mediated coronary vasodilation was studied in isolated hearts from young (1-2 months) and mature (12-18 months) Wistar rats. The nonselective agonist 5'-N-ethylcarboxamidoadenosine (NECA) induced biphasic concentration-dependant dilation with similar potencies in both age groups (p < 0.05). Despite similar potencies, responses to NECA were significantly depressed by 50% with age. NECA-mediated dilation was unaltered by selective A adenosine receptor (A1AR) antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 100 nM ) or A adenosine receptor (A2AAR) antagonist 5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5- ]pyrimidine (SCH 58261, 100 nM ). However, the A2B adenosine receptor (A2B AR) selective antagonist alloxazine (10 microM ) significantly reduced response magnitude to NECA in both age groups. Concentration-response curves to N -2-(4-aminophenyl) ethyladenosine (APNEA) induced biphasic concentration-dependent dilation in hearts from young animals. In the presence of the three combined antagonists, 1 microM DPCPX, 100 nM SCH 58261, and 1 microM alloxazine, the response magnitude was significantly attenuated (p < 0.05). The addition of the A3 adenosine receptor (A3AR) antagonist 3-ethyl-5-benzyl-2-methyl-4-phenylethyl-6-phenyl-1,4-(+/-)-dihydropyridine-3,5-dicarboxylate (MRS1191, 100 nM ) to the combined antagonists further attenuated vasodilator responses to APNEA. The results suggest that multiple adenosine receptor subtypes mediate dilation in the rat coronary circulation. NECA mediates vasodilation via the A2BAR subtype, while dilator responses to APNEA in the presence and absence of A1, A2, and A3 ARs antagonists provide evidence for a vasodilator role for A3 ARs in rat coronary circulation. The magnitude of the coronary dilator response is reduced with age and does not involve A2A or A1 ARs.

Systemic depletion of macrophages by liposomal bisphosphonates reduces neointimal formation following balloon-injury in the rat carotid artery.

Abstract: OBJECTIVES Macrophage depletion by liposomal clodronate inhibits neointimal formation after balloon-injury. The present study examined bisphosphonates (BPs) potency-effect relationship and the role of systemic versus local monocytes in vascular repair. METHODS AND RESULTS Liposomal preparations of clodronate, pamidronate, alendronate, and ISA-13-1 inhibited RAW-264 macrophages growth in a dose-response manner. Administration to balloon-injured rats suppressed neointimal growth. Neointima to media ratio (N/M) at 14 days was reduced from 1.35 +/- 0.22 (control) to 0.4 +/- 0.1 and 0.9 +/- 0.17 by liposomal alendronate (1.5 mg/kg, i.v.) and liposomal ISA-13-1 (15 mg/kg), respectively (n = 8-10, P < 0.05). Suppression of neointimal formation was preserved at 30 days. Subcutaneous administration of liposomal BP (LBP) was also effective in suppressing neointimal formation, while short local intraluminal application had no effect. Immunostaining for ED-1 and ED-2 revealed no resident macrophages in the arterial wall, and reduced macrophage infiltration in LBP-treated animals. Arterial PDGF-B chain and PDGF-beta receptor activation were reduced in LBP-treated animals and up-regulation of the PDGF receptor was noted. CONCLUSIONS Systemic transient inactivation of monocytes and macrophages by LBPs reduced macrophage infiltration and neointimal formation in the rat carotid injury model. The findings demonstrate a BP potency-effect relationship, and highlight the role of circulating monocytes in vascular injury and repair.

Selective A2a Adenosine Receptor Agonist as a Coronary Vasodilator in Conscious Dogs: Potential for Use in Myocardial Perfusion Imaging

Abstract: The authors sought to demonstrate the advantages of a selective, potent, short-acting A adenosine receptor agonist, CVT-3146 (2-(N-pyrazolyl)Ado derivative), for potential clinical use as a coronary vasodilator during myocardial perfusion imaging The use of adenosine in a pharmacological stress test during myocardial imaging is limited by side effects mediated by A1 and A2B adenosine receptors and by its ultrashort duration of action CVT-3146 (01-5 microg/kg) and adenosine (13-267 microg/kg) were given as peripheral intravenous injections in 10 awake dogs instrumented for measurement of coronary blood flow (CBF) CVT-3146 caused a dose-dependent increase of CBF (ED50 = 034 +/- 008 microg/kg, maximal increase = 221 +/- 18%, n = 6) Adenosine was less potent (ED = 51 +/- 15 microg/kg, p < 005) but equieffective (maximal increase in CBF = 227 +/- 11%) The increase in CBF caused by 25 microg/kg CVT-3146 reached 84 +/- 5% of the maximal reactive hyperemia following 20 s of coronary occlusion (n = 4) After a 10-s injection of CVT-3146 (25 microg/kg), the increase in CBF remained at least twofold above baseline for 97 +/- 14 s, whereas for adenosine (267 microg/kg), the twofold increase in CBF lasted only 24 +/- 2 s (p < 001, n = 6) A 30-s injection of 25 microg/kg CVT-3146 prolonged the twofold increase in CBF up to 221 +/- 20 s No atrioventricular block was noted At 25 microg/kg, the peak effect of CVT-3146 on CBF was associated with a short-lasting (20 +/- 6 s) increase in heart rate (78 +/- 9 bpm) and decrease in mean arterial blood pressure (13 +/- 6 mm Hg, p < 005, n = 6) CVT-3146 is a potent coronary vasodilator Its short duration of action, minimal and transient systemic hemodynamic effects, and ease of administration may make this agonist suitable for pharmacological coronary vasodilation during myocardial perfusion imaging for noninvasive detection of subcritical arterial stenosis

Rosuvastatin, a New HMG-CoA Reductase Inhibitor, Protects Ischemic Reperfused Myocardium in Normocholesterolemic Rats

Abstract: :The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have been shown to upregulate endothelial nitric oxide synthase in isolated endothelial cells in a manner that is independent of their lipid-lowering effects. Nitric oxide inhibits polymorphonuclear leukocyte (PMN) adh

Elevated levels of the serum endogenous inhibitor of nitric oxide synthase and metabolic control in rats with streptozotocin-induced diabetes.

Abstract: This study was designed to determine the relationship between elevated levels of the endogenous inhibitor of nitric oxide synthase, asymmetric dimethylarginine (ADMA), and metabolic control in rats with streptozotocin-induced diabetes. Serum levels of ADMA were measured by high-performance liquid chromatography at 8 weeks after diabetes was induced. Endothelium-dependent relaxation to acetylcholine was tested in aortic rings from nondiabetic age-matched control, untreated diabetic, and insulin-treated diabetic rats to evaluate endothelial function. Serum concentrations of glucose, glycosylated serum protein, and malondialdehyde were examined to estimate metabolic control. Serum levels of ADMA increased dramatically in untreated diabetic rats compared with control rats. This elevation in ADMA levels was accompanied by impairment of the endothelium-dependent relaxation response to acetylcholine in aortic rings. Long-term insulin treatment not only prevented the elevation of serum ADMA levels, but also improved the impairment of endothelium-dependent relaxation in diabetic rats. Serum levels of glucose, glycosylated serum protein, and malondialdehyde were significantly increased in parallel with the elevation of ADMA in untreated diabetic rats compared with control rats. These parameters were normalized after diabetic rats received insulin treatment for 8 weeks. These results provide the first evidence that an elevation in the concentration of ADMA in rats with streptozotocin-induced diabetes is closely related to metabolic control of the disease.

ETA receptors mediate vasoconstriction of large conduit arteries during reduced flow in humans.

Abstract: Vascular tone is regulated by endothelium-derived vasodilating and constricting substances, mainly nitric oxide and endothelin (ET)-1. These 2 mediators, which antagonize the actions of each other, are released in response to shear-stress produced by blood flow. The aim of this study was to delineate the contribution of endogenous ET-1 on vascular tone of a large conduit artery during reduced and hyperemic flow. Radial artery diameter was continuously measured with a high-resolution ultrasonic echo-tracking device in 8 healthy subjects. After establishing stable baseline conditions, a wrist cuff was inflated to suprasystolic pressure for 5 minutes. In another 5 subjects, measurements were obtained during intraarterial infusion of saline or an ETA receptor antagonist (BQ-123, 1 nmol/min) in a dosage not affecting basal radial diameter. Wrist occlusion caused a progressive vasoconstriction of the radial artery (P = 0.0001). Vasoconstriction of the radial artery during wrist occlusion was significantly attenuated by ETA receptor antagonism (-2.7% +/- 0.6% versus -6.8% +/- 0.6% during saline, P = 0.007). Flow-mediated vasodilation was not influenced by BQ-123 (7.5% +/- 0.8% versus 7.8% +/- 1.1%, P = NS). This study demonstrates active vasoconstriction of large conduit arteries during conditions of reduced blood flow via ETA receptoractivation. This may play an important role in disease states with reduced systemic or local blood flow and indicates the therapeutic potential of ETA receptor antagonism.

Clinical implication of morning blood pressure surge in hypertension

Abstract: Cardiovascular events occur most frequently in the morning. The morning surge in blood pressure may be associated with hypertensive target organ damage and subsequent cardiovascular risk in hypertensive patients. In our prospective study on elderly hypertensive patients, the morning blood pressure surge (defined as the increase from the lowest blood pressure during sleep to the average of the first 2 h after waking) was significantly associated with silent hypertensive cerebrovascular disease and subsequent stroke risk. This association was independent of age and 24-h ambulatory blood pressure levels. In addition, even after controlling for these factors and status of silent cerebrovascular disease, the contribution of the morning blood pressure surge remained significant, and a 10 mmHg increase in systolic morning blood pressure surge increase the stroke risk by 22%. A related factor is orthostatic hypertension, which might be associated with increased sympathetic activity, and which is significantly associated with an increase in morning blood pressure surge and ambulatory blood pressure variability. A possible implication is that, in addition to strict blood pressure control, antihypertensive medication that targets exaggerated morning blood pressure may achieve more effective prevention of cardiovascular events in hypertensive patients.

Vasodilative effects of urocortin II via protein kinase A and a mitogen-activated protein kinase in rat thoracic aorta.

Abstract: Summary: Four corticotropin-releasing factor (CRF)–related peptides have been found in mammals and are known as CRF, urocortin, urocortin II, and urocortin III (also known as stresscopin). The three urocortins have considerably higher affinities for CRF receptor type 2 (CRF R2) than CRF, and urocortin II and urocortin III are highly selective for CRF R2. In the present study, the authors examined the hypothesis that urocortin II or urocortin III, in addition to urocortin, produces vasodilation as a candidate for natural ligands of CRF R2β in rat thoracic aorta. Involvement of protein kinases on urocortin-induced vasodilation was also explored. The vasodilative effects of urocortin II and urocortin III were more potent than that of CRF, but less potent than that of urocortin. Urocortin II–induced vasodilation was significantly attenuated by a CRF R2–selective antagonist, antisauvagine-30. Both SQ22536, an adenylate cyclase inhibitor, and Rp-8-Br-cAMPS, a protein kinase A (PKA) inhibitor, were found to attenuate the urocortin II–induced vasodilation. SB203580, a p38 mitogen-activated protein (MAP) kinase inhibitor, also inhibited the effects of urocortin and urocortin II on vasodilation. Thus, urocortins contribute to vasodilation via p38 MAP kinase as well as PKA pathways.

Chronic endothelin receptor blockade prevents both early hyperfiltration and late overt diabetic nephropathy in the rat.

Abstract: Diabetic nephropathy is associated with enhanced renal synthesis of endothelin (ET)-1. The goal of this study was to investigate the effects of dual ET receptor antagonism in the early phase (2 months) and in the late phase (5 months) of diabetic nephropathy in rats, and to compare this approach to angiotensin-converting enzyme inhibition. Four groups of uninephrectomized streptozotocin-induced diabetic rats were assigned to receive orally vehicle, bosentan, enalapril, or their combination. A fifth group consisted of nondiabetic, uninephrectomized rats. At 2 weeks, untreated diabetic rats exhibited increased glomerular filtration rate and renal plasma flow. Bosentan, enalapril, and the combination all prevented hyperfiltration and hyperperfusion. By 5 months, diabetic rats developed marked increases in mean arterial pressure and renal vascular resistance, progressive proteinuria, and renal structural damage with glomerular sclerosis and hypertrophy. Bosentan completely prevented the development of hypertension and renal vasoconstriction, and largely prevented the development of proteinuria and renal structural injury. The renal protective effect of bosentan was comparable to that of enalapril or the combination, although its anti-proteinuric effect was less. Clinical studies are warranted to assess whether ET receptor antagonism can have additive effects on top of ACE inhibition, the current treatment of choice in diabetic nephropathy.

Role of nitric oxide in the renal protective effects of ischemic preconditioning.

Abstract: Possible involvement of nitric oxide (NO) in the protective effect of ischemic preconditioning against the ischemia/reperfusion-induced acute renal failure was investigated. Ischemic preconditioning, which consists of three cycles of 2-minute ischemia followed by 5-minute reperfusion, was performed prior to 45-minute ischemia. Ischemic preconditioning significantly improved the renal dysfunction induced by 45-minute ischemia followed by 24-hour reperfusion. Histopathological examination of the kidney of ischemia/reperfusion rats revealed severe renal damage, and suppression of the damage was seen with the ischemic preconditioning treatment. NO metabolites (NOx) production in the kidney after 45-minute ischemia and reperfusion was markedly increased in ischemia/reperfusion rats with ischemic preconditioning, compared with animals not subjected to ischemic preconditioning, and these increases correlated with changes in endothelial NO synthase (eNOS) protein expression in renal tissues. The improvement of renal dysfunction in ischemic preconditioning rats was abolished by the pretreatment with N G -nitro-L-arginine, a nonselective NOS inhibitor, but not with aminoguanidine, an inducible NOS inhibitor. In addition, increment of endothelin-1 (ET-I) content in the kidney after the reperfusion was markedly suppressed by ischemic preconditioning treatment. These findings suggest that the protective effect of ischemic preconditioning on ischemia/reperfusion -induced acute renal failure is closely related to the renal nitric oxide production following the increase in eNOS expression after the reperfusion and that the suppressive effect of ischemic preconditioning on the ischemia/reperfusion -induced renal ET-1 overproduction may be partly involved in the ameliorating effect of ischemic preconditioning.

Endogenous adenosine increases coronary flow by activation of both A2A and A2B receptors in mice.

Abstract: To clarify which adenosine receptor subtype(s) are responsible for regulation of coronary flow through endogenous adenosine, coronary vascular responses were examined in isolated hearts from wild-type (WT) and A(2A) knockout (A(2A)KO) mice. Adenosine deaminase inhibitor, erythro-9-hydroxy-nonyl-adenine (EHNA), and adenosine kinase inhibitor, iodotubericidine (ITU), were used to examine the effects of endogenous adenosine. Combined infusion of EHNA and ITU in Balb/c hearts produced comparable increases in coronary flow as exerted by exogenous adenosine while they markedly decreased the heart rate, and these effects were reversed by adenosine receptor antagonist, 8-p-sulfophenyl-theophylline (8-SPT). Similarly, EHNA and ITU increased coronary flow in WT hearts to 422% of baseline, whereas this response was reduced to 144% of baseline in A(2A)KO hearts. Heart rate was equally reduced (approximately 50% of baseline) in both groups. Alloxazine (A(2B) receptor antagonist) abolished EHNA- and ITU-induced coronary flow in A(2A)KO hearts without altering the reduced heart rate. Selective A(1) receptor antagonist, 8-cyclopentyl-1-1,3-dipropylxanthine (DPCPX), reversed EHNA- and ITU-induced decreases in heart rate without altering the elevated coronary flow. These findings suggest that coronary vascular responses to endogenous adenosine mimic those produced by exogenous adenosine and are mediated at least by activation of both A(2A) and A(2B) receptors in isolated mouse hearts.