title: Evoked changes in cardiovascular function in rats by infusion of levosimendan, OR-1896 [(R)-N-(4-(4-methyl-6-oxo-1,4,5,6-tetrahydropyridazin-3-yl)phenyl)acetamide], OR-1855 [(R)-6-(4-aminophenyl)-5-methyl-4,5-dihydropyridazin-3(2H)-one], dobutamine, and milrinone: comparative effects on peripheral resistance, cardiac output, dP/dt, pulse rate, and blood pressure.
abstract: Levosimendan enhances cardiac contractility primarily via Ca(2+) sensitization, and it induces vasodilation through the activation of ATP-sensitive potassium channels and large conductance Ca(2+)-activated K(+) channels. However, the concentration-dependent hemodynamic effects of levosimendan and its metabolites (R)-N-(4-(4-methyl-6-oxo-1,4,5,6-tetrahydropyridazin-3-yl)phenyl)acetamide (OR-1896) and (R)-6-(4-aminophenyl)-5-methyl-4,5-dihydropyridazin-3(2H)-one (OR-1855) have not been well defined. Thus, levosimendan (0.03, 0.10, 0.30, and 1.0 mumol/kg/30 min; n = 6) was infused as four escalating 30-min i.v. doses targeting therapeutic to supratherapeutic concentrations of levosimendan (C(max), approximately 62.6 ng/ml); metabolites were infused at one-half log-unit lower doses and responses compared to dobutamine (beta(1)-agonist) and milrinone (phosphodiesterase 3 inhibitor). Peak concentrations of levosimendan, OR-1896, and OR-1855 at the end of the high dose were 323 +/- 14, 83 +/- 2, and 6 +/- 2 ng/ml, respectively (OR-1855 rapidly metabolized to OR-1896; peak = 82 +/- 3 ng/ml). Levosimendan and OR-1896 produced dose-dependent reductions in blood pressure and peripheral resistance with a rank potency, based on ED(15) values, of OR-1896 (0.03 mumol/kg) > OR-1855 > levosimendan > milrinone (0.24 mumol/kg); an ED(15) for dobutamine could not be defined. Only dobutamine produced increases in pulse pressure (30 +/- 5%) and rate-pressure product (34 +/- 4%). All of the compounds, with the exception of OR-1855, elicited dose-dependent increases in dP/dt with a rank potency, based on ED(50) values, of dobutamine (0.03 mumol/kg) > levosimendan > OR-1896 > milrinone (0.09 mumol/kg), although only levosimendan produced sustained increases in cardiac output (9 +/- 4%). Thus, levosimendan and OR-1896 are hemodynamically active at sub- to supratherapeutic concentrations (whereas the effects of OR-1855 in the rat are thought to be predominantly mediated by conversion to OR-1896) and produce direct inotropic effects and also direct relaxation of the peripheral vasculature, which clearly differentiates them from dobutamine, which does not elicit K(+) channel activation, suggesting a more balanced effect on the cardiac-contractile state and K(+) channel-mediated changes in vascular resistance.
authors.affiliation: Department of Integrative Pharmacology, R46R, Global Pharmaceutical Research and Development, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, IL 60064-6119, USA.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Segreti
authors.forename: Kennan C
authors.initials: KC
authors.lastname: Marsh
authors.forename: James S
authors.initials: JS
authors.lastname: Polakowski
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Fryer
mesh_terms: D000818:Animals; D001794:Blood Pressure; D002302:Cardiac Output; D002316:Cardiotonic Agents; D002320:Cardiovascular Physiological Phenomena / Q000187:drug effects*; D004280:Dobutamine / Q000008:administration & dosage / Q000494:pharmacology*; D004338:Drug Combinations; D006339:Heart Rate; D006439:Hemodynamics / Q000187:drug effects*; D006835:Hydrazones / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D020105:Milrinone / Q000008:administration & dosage / Q000494:pharmacology*; D009200:Myocardial Contraction; D011724:Pyridazines / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077464:Simendan; D014655:Vascular Resistance
chemical_list: D002316:Cardiotonic Agents; D004338:Drug Combinations; D006835:Hydrazones; D011724:Pyridazines; D000077464:Simendan; D004280:Dobutamine; D020105:Milrinone