Calcium-dependent vasorelaxant capacity of levosimendan in porcine and human epicardial coronary artery preparations

The Novel Inodilator ORM-3819 Relaxes Isolated Porcine Coronary Arteries: Role of Voltage-Gated Potassium Channel Activation

Relaxation and changes in the transmembrane potential of vascular smooth muscle induced by ORM-3819, a novel inodilating compound, were investigated in isolated porcine coronary arteries. Isometric tone was studied on arterial rings precontracted by KCl (30 mM), and resting membrane potential was investigated by a conventional microelectrode technique. ORM-3819 in the concentration range 0.38-230.6 µM evoked concentration-dependent relaxation with a maximum value of 58.1% and an effective concentration of the relaxing substance that caused 50% of maximum relaxation of 72.2 µM. The maximum hyperpolarization produced by ORM-3819 at a concentration of 120 µM (-2.6 ± 0.81 mV, N = 10) did not differ significantly from that induced by C-type natriuretic peptide (CNP), an endogenous hyperpolarizing mediator, at a concentration of 1.4 µM (-3.6 ± 0.38 mV, N = 17). The same effect elicited by the known inodilator levosimendan was less pronounced at a concentration of 3.7 µM: -1.82 ± 0.44 mV, N = 22 (P < 0.05 vs. CNP). The voltage-gated potassium channel inhibitor 4-aminopyridine, at a concentration of 5 mM, attenuated the relaxation induced by ORM-3819 at concentrations of 41.6 or 117.2 µM. These results suggest that ORM-3819 is a potent vasodilating agent able to relieve coronary artery vasospasm by causing hyperpolarization of vascular smooth muscle cells through processes involving activation of voltage-gated potassium channels.

Effects of levosimendan on isolated human internal mammary artery and saphenous vein: concurrent use with conventional vasodilators

Graft spasm is a common problem in coronary artery bypass grafting (CABG). In this study, we aimed to investigate the interaction of levosimendan, a novel inodilator, with vasodilator agents that are clinically used for the treatment of graft spasm and with endogenous vasoconstrictors that are thought to play a role in graft vasospasm, in human internal mammary artery (IMA) and saphenous vein (SV). Isolated human IMA and SV segments derived from patients undergoing CABG were suspended in an organ bath. Responses to cumulative concentrations of noradrenaline (NA), serotonin (5-HT), papaverine, nitroglycerin (NG), and diltiazem were recorded before and after 10(-5) m levosimendan incubation (30 min). In addition, cumulative levosimendan responses were taken in vessels precontracted with NA or 5-HT. 10(-5) m levosimendan reduced NA Emax and sensitivity in IMA and SV, and 5-HT Emax responses in IMA. Moreover, levosimendan caused concentration-dependent relaxation in both grafts. Papaverine Emax or sensitivity was not altered by levosimendan neither in IMA nor in SV. Levosimendan diminished NG sensitivity in IMA and Emax responses in SV and decreased diltiazem Emax responses both in IMA and SV. Our results suggest that levosimendan may be used alone for prevention or treatment of graft spasm in IMA or in combination with papaverine in IMA and SV grafts. However, as concurrent administration with diltiazem or NG causes a reduction in relaxation in vitro, we suggest caution should be exercised when using levosimendan in combination with these agents.

Levosimendan alone and in combination with valsartan prevents stroke in Dahl salt-sensitive rats

The effects of levosimendan on cerebrovascular lesions and mortality were investigated in models of primary and secondary stroke. We aimed to determine whether the effects of levosimendan are comparable to and/or cumulative with those of valsartan, and to investigate whether levosimendan-induced vasodilation has a role in its effects on stroke. In a primary stroke Dahl/Rapp rat model, mortality rates were 70% and 5% for vehicle and levosimendan, respectively. Both stroke incidence (85% vs. 10%, P<0.001) and stroke-associated behavioral deficits (7-point neuroscore: 4.59 vs. 5.96, P<0.001) were worse for vehicle compared to levosimendan. In a secondary stroke model in which levosimendan treatment was started after cerebrovascular incidences were already detected, mean survival times were 15 days with vehicle, 20 days with levosimendan (P=0.025, vs. vehicle), 22 days with valsartan (P=0.001, vs. vehicle), and 31 days with levosimendan plus valsartan (P<0.001, vs. vehicle). The respective survivals were 0%, 16%, 20% and 59%, and the respective incidences of severe lesions were 50%, 67%, 50% and 11%. In this rat model, levosimendan increased blood volume of the cerebral vessels, with significant effects in the microvessels of the cortex (∆R=3.5±0.15 vs. 2.7±0.17ml for vehicle; P=0.001) and hemisphere (∆R=3.2±0.23 vs. 2.6±0.14ml for vehicle; P=0.018). Overall, levosimendan significantly reduced stroke-induced mortality and morbidity, both alone and with valsartan, with apparent cumulative effects, an activity in which the vasodilatory effects of levosimendan have a role.

Interspecies Differences and Extracellular Calcium Dependence in the Vasorelaxing Effect of Cromakalim in Isolated Human, Porcine, and Canine Coronary Arteries

Coronary arteries isolated from human, porcine, and canine hearts were depolarized with potassium chloride and relaxed by cromakalim (0.0125-10.0 μmol/L) at low (1.5 mmol/L) and high (7.5 mmol/L) extracellular calcium concentration ([Ca2+] o). At low [Ca2+]o, cromakalim (1 μmol/L) relaxed the coronary arteries with the order of porcine > canine > human. Fifty percent effective concentrations of cromakalim revealed the same order: 0.15 μmol/L in porcine, 0.36 μmol/L in canine, and 3.91 μmol/L in human coronary arteries. High [Ca2+]o significantly enhanced the relaxing effect and decreased the potency of cromakalim in porcine and human but not in canine coronary arteries. In human coronary arteries, precontracted with the prostaglandin analogue (U46619), high [Ca2+] o enhanced the effect of 0.1 μmol/L cromakalim more efficiently in the presence than in the absence of endothelium. It appears that the coronary dilating effect of cromakalim largely depends on the species and is modulated by [Ca2+]o, with a partly endothelium dependent manner.

Vasorelaxing effect of levosimendan against 5-hydroxytryptamine-induced contractions in isolated human conduit bypass grafts

Levosimendan is a novel inodilator drug developed for the treatment of heart failure. The possible vasodilating property of the drug in human coronary artery bypass grafts was investigated. Isometric tensions of the left internal thoracic artery (LITA, n = 8) as well as the proximal and distal segments of the radial artery (RA, n = 8 and 8) were measured in isolated organ baths. Concentration-relaxation curves for levosimendan (0.009-1.14 μmol L−1) were obtained against 5-hydroxytryptamine (5-HT; serotonin, 0.002–9.3 μmol L 1)-induced contractions. 5-HT-induced contraction of LITA was considerably smaller than that of the proximal and distal RAs. Levosimendan relaxed the grafts in the following order of calculated maximum efficacies (Emax): LITA &gt; proximal RA &gt; distal RA (LITA 100.3 ±16.2% of 5-HT-induced maximum tension, proximal RA 86.9 ±8.6%, distal RA 59.4 ± 17.5%, P &lt; 0.05 LITA vs distal RA). The potency values of levosimendan, expressed as the negative logarithm of 50% effective concentrations (pD2), were comparable in the three bypass grafts (LITA −6.52 ± 0.44 log mol L−1, proximal RA −6.60 ± 0.49 log mol L−1, distal RA −6.85 ± 0.45 log mol L−1). The results suggest that levosimendan is an effective vasorelaxant of conduit bypass grafts and may serve as a new therapeutic tool, especially in the case of LITA and proximal RA grafts, for relieving perioperative spasm and subsequent graft failure.

The gender differences in the relaxation to levosimendan of human internal mammary artery

PURPOSE

The mechanism of the vasorelaxation to levosimendan varies depending on the vascular bed and species studied. Here, we examined the vasorelaxation to levosimendan as well as its modification by various potassium channel antagonists in human internal mammary artery (IMA) obtained from male and female patients.

METHODS

IMA grafts were supplied from 27 male and 19 age-matched female patients undergoing coronary bypass operation. The contraction to noradrenaline and relaxation to levosimendan were studied in IMA rings obtained from both gender. The relaxations to levosimendan were also assessed in the presence of glibenclamide (10 microM), an adenosine triphosphate-sensitive potassium channel (K(ATP)) blocker, or charybdotoxin (100 nM), a calcium-activated potassium channel (K(Ca)) blocker, or 4-aminopyridine(1 mM), a voltage-sensitive potassium channel (K(v)) inhibitor.

RESULTS

Concentration-response curves to noradrenaline were not different in IMA rings from either gender. Pretreatment with levosimendan (3 x 10(-7) M) slightly modified the contractions to noradrenaline in both gender. Levosimendan (10(-9)-10(-5) M) produced concentration-dependent relaxation in IMA rings, contracted by noradrenaline (5 x 10(-6) M), from males and females. The vasodilatory effects of levosimendan were more pronounced in the arteries from males (83%) than females (69%), in term of the maximal relaxation (E (max)). Charybdotoxin and glibenclamide significantly inhibited the relaxation to levosimendan in the arteries from males but not in those of females.

CONCLUSIONS

The vasodilating efficacy of levosimendan and its relaxation mechanism differs between the arteries from males and females, which may have clinical consequences in the treatment of heart failure.

The Role of Potassium Channels in Relaxant Effect of Levosimendan in Rat Small Mesenteric Arteries

We investigated both the effect of levosimendan and the role of various potassium channels in KCl-precontracted rat small mesenteric arteries. Levosimendan (10(-6)-10(-3) M) or cromakalim (CRO, 10(-7)-10(-4) M) produced concentration-dependent relaxation responses in small mesenteric arteries precontracted by 30 mM KCl. The relaxant responses to levosimendan in KCl-precontracted arteries did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation of rat small mesenteric arterial segments with ATP-dependent potassium channel (KATP) blocker glibenclamide (GLI, 10(-6) M) for 30 min significantly inhibited the relaxant responses to both levosimendan and CRO. Neither the Ca(2+)-activated potassium channel (KCa) blocker iberiotoxin (10(-7) M) nor the voltage-dependent potassium channel (KV) blocker 4-aminopyridine (5 mM) incubation for 30 min caused significant alterations in relaxant responses to levosimendan in KCl-precontracted small mesenteric arteries. These findings suggested that levosimendan-induced relaxation responses in isolated rat small mesenteric arteries were neither depended on endothelium nor inhibited by the blockers of KV or KCa but, they rather seem to depend on the activation of KATP.

Levosimendan improves hemodynamics and coronary flow reserve after percutaneous coronary intervention in patients with acute myocardial infarction and left ventricular dysfunction

BACKGROUND

Positive inotropic agents may be associated with increasing myocardial ischemia or malignant arrhythmias. Levosimendan, a new calcium sensitizer, with its little effect on myocardial oxygen demand is better tolerated by patients with acute coronary syndromes. We evaluated the acute effects of levosimendan on hemodynamics and coronary flow velocities in patients with left ventricular (LV) dysfunction undergoing percutaneous coronary interventions (PCIs) for an acute myocardial infarction (AMI).

METHODS

Patients with AMI and LV dysfunction undergoing primary PCI were randomized to intravenous infusion of levosimendan (10 minutes bolus with 12 microg/kg followed by 0.1 microg/kg per minute for 24 hours) or placebo, 10 minutes after a primary PCI. Evaluation of hemodynamics and of coronary flow reserve (CFR) were performed at baseline and after bolus.

RESULTS

Twenty-six consecutive patients (mean age 57 +/- 5.4 years, 18 males) were included into the study. At baseline, mean values of hemodynamics and coronary flow velocities were comparable between groups. After bolus, patients with levosimendan (n = 12) showed a significant decrease of pulmonary capillary wedge pressure (from 24 to 19 mm Hg) and a significant increase of cardiac index (from 1.8 to 2.4 L/m2 per minute) resulting in a significant decrease of systemic vascular resistance (from 1366 to 1075 [dyne . s]/cm2). Moreover, CFR on infarct-related artery and on reference vessel significantly improved in patients treated with levosimendan (from 1.6 to 2.0 and from 2.1 to 2.4, respectively). On the other hand, no statistically significant changes have been observed in the placebo group (n = 14).

CONCLUSIONS

Levosimendan, given intravenously after a PCI procedure in patients with AMI and LV dysfunction, significantly improves hemodynamics and CFR, compared with placebo.

Contractile action of levosimendan and epinephrine during acidosis

We evaluated the inotropic actions of levosimendan and epinephrine, both singly and in combination, under isohydric (pH 7.4) and acidotic (pH 7.0) conditions in isolated guinea-pig hearts. Acidosis depressed contractility and myocardial relaxation by 25-30%, and both inotropes were less efficacious at pH 7.0, while their potencies were unaffected. In combination experiments, the presence of levosimendan increased the potency of epinephrine approximately 17-fold (pH 7.4) and 11-fold (pH 7.0), and the presence of epinephrine increased the potency of levosimendan approximately 12-fold (pH 7.4) and approximately 21-fold (pH 7.0). At pH 7.0, both inotropes augmented papillary muscle contraction to a similar extent, but in contrast to epinephrine, levosimendan non-significantly [corrected] raised cAMP levels. In conclusion, combining levosimendan with epinephrine helps to overcome the depressed inotropic actions of epinephrine during acidosis, suggesting that additional studies which might justify clinical evaluation of the concurrent use of the two agents should be performed.

ATP-dependent potassium channels as a key target for the treatment of myocardial and vascular dysfunction

PURPOSE OF REVIEW

The aim of this review is to highlight the most recent and interesting articles on the physiologic properties and functions of ATP-dependent potassium channels in the cardiovascular system and on the role of the potassium channel openers for the treatment of cardiovascular dysfunction.

RECENT FINDINGS

The initial efforts in the development of potassium channel openers focused on the management of systemic hypertension. Lately, the range of possible indications for potassium channel openers has increased to include pulmonary hypertension and stable angina pectoris. The discovery of a connection between the mitochondrial ATP-dependent potassium channels and the phenomenon of cardiac preconditioning created potential new uses for potassium channel openers in myocardial ischemia, inn unstable angina, in preoperative and perioperative settings, and for the preservation of organs for transplant.

SUMMARY

The most recent data on the physiologic roles of sarcolemmal and mitochondrial ATP-dependent potassium channels and the pharmacology of potassium channel openers in the cardiovascular system are summarized and discussed. Finally, the effects of potassium channel opener drugs including minoxidil, nicorandil, pinacidil, bimakalin, and levosimendan, a dual-action potassium channel opener and calcium sensitizer with inodilator and cardioprotective activity, are discussed.

Levosimendan: a review of its use in the management of acute decompensated heart failure

Levosimendan (Simdax) is a calcium-sensitising drug that stabilises the troponin molecule in cardiac muscle, thus prolonging its effects on contractile proteins, with concomitant vasodilating properties. Intravenous levosimendan (12-24 microg/kg loading dose followed by 0.1-0.2 microg/kg/min for 24 hours, adjusted for response and tolerability) is approved for the short-term treatment of acute severe decompensated heart failure. Cardiac output increased by about 30% and pulmonary capillary wedge pressure and systemic vascular resistance decreased by about 17-29% in patients with decompensated heart failure receiving intravenous levosimendan. In large, well controlled trials in patients with decompensated heart failure, intravenous levosimendan was significantly more effective than placebo or dobutamine for overall haemodynamic response rate (primary endpoint). Significant benefits were also seen for mortality (versus placebo or dobutamine) and for the combined risk of worsening heart failure or death (versus dobutamine). Improvements in key symptoms (dyspnoea and fatigue) have not been consistently demonstrated. Hospitalisation costs were similar for levosimendan and dobutamine; the total incremental (hospitalisation plus drug) cost per life-year saved (extrapolated to 3 years) for levosimendan relative to dobutamine was estimated at Euro 3205 (year of costing 2000). Levosimendan is generally well tolerated, with an adverse event profile at recommended dosages similar to that in patients receiving placebo. Cardiac rate/rhythm disorders and headache were the most common events. At higher dosages, patients receiving levosimendan had higher rates of sinus tachycardia than those in placebo recipients. More patients receiving dobutamine than those receiving levosimendan experienced angina pectoris/chest pain/myocardial ischaemia or rate/rhythm disorders.

CONCLUSION

Intravenous levosimendan is an effective calcium-sensitising drug with vasodilatory and inotropic effects, and superior efficacy/tolerability to those of intravenous dobutamine in patients with acute decompensated heart failure. It may be associated with reduced mortality compared with both placebo and dobutamine. Levosimendan is generally well tolerated and may have less potential for cardiac rate/rhythm disorders than dobutamine. While evidence from well designed trials confirming the improved mortality over dobutamine and investigating haemodynamic efficacy and mortality versus other positive inotropes is required, intravenous levosimendan appears to be a useful addition to the treatment options for acute decompensated heart failure in patients with low cardiac output.