title: Investigation on SCH00013, a novel cardiotonic agent with Ca++ sensitizing action. 3rd communication: stereoselectivity of the enantiomers in cardiovascular effects.
abstract: The cardiovascular effects of the enantiomers, (+)-SCH00013 and (-)-SCH00013, of a novel cardiotonic agent 4,5-dihydro-6-[1-[2-hydroxy-2-(4-cyanophenyl)ethyl]- 1,2,5,6-tetrahydropyrido-4-yl]pyridazin-3(2H)-one (SCH00013) were investigated in vitro and in vivo. The enantiomers of SCH00013 elicited an equipotent positive inotropic effect in isolated guinea-pig papillary muscles. Both of the enantiomers had a modest negative chronotropic effect in isolated guinea-pig right atria and the difference in the chronotropic effects of the enantiomers was not significant. In anesthetized dogs, both enantiomers increased LVdP/dtmax without change in heart rate and slightly decreased blood pressure. These hemodynamic effects of the enantiomers were not significantly different from each other. (+)-SCH00013 and (-)-SCH00013 increased the extent of cell shortening in association with only a small increase in the Ca++ transients in indo-1-loaded rabbit cardiomyocytes, and both the increases in cell shortening and Ca++ transients were not significantly different between the enantiomers. Both isomers equally shifted the relationships between the increases in the cell shortening and Ca++ transients to the left and upward as compared with the relationships for the elevation of extracellular Ca++ concentration and isoproterenol, which indicates that the effectiveness of the Ca++ sensitizing effects of the enantiomers are almost equivalent. The enantiomers of SCH00013 showed equipotent inhibitory effect on the phosphodiesterase (PDE) III activity. The maximal extent and the potency of prolonging effect of the two enantiomers on the effective refractory period were also the same. Thus, the efficacy and potency of the effects on the cardiovascular parameters such as myofibrillar Ca++ sensitivity, PDE III activity and the effective refractory period for the both enantiomers of SCH00013 are equivalent, indicating that the cardiovascular effects of SCH00013 may be due to equal contribution of both enantiomers.
authors.affiliation: Research Laboratory, Zenyaku Kogyo Co. Ltd., Tokyo, Japan. sugawara@zenyaku.co.jp
authors.forename: H
authors.initials: H
authors.lastname: Sugawara
authors.forename: M
authors.initials: M
authors.lastname: Hino
authors.forename: A
authors.initials: A
authors.lastname: Yoshimura
authors.forename: K
authors.initials: K
authors.lastname: Yoshioka
authors.forename: M
authors.initials: M
authors.lastname: Sakato
authors.forename: M
authors.initials: M
authors.lastname: Endoh
mesh_terms: D000758:Anesthesia; D000818:Animals; D002120:Calcium Channel Agonists / Q000737:chemistry / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects; D002316:Cardiotonic Agents / Q000737:chemistry / Q000494:pharmacology*; D004095:Dihydropyridines / Q000737:chemistry / Q000494:pharmacology*; D004285:Dogs; D005260:Female; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000201:enzymology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011724:Pyridazines / Q000737:chemistry / Q000494:pharmacology*; D011817:Rabbits; D012032:Refractory Period, Electrophysiological / Q000187:drug effects; D013237:Stereoisomerism
chemical_list: D002120:Calcium Channel Agonists; D015220:Calcium Channels; D002316:Cardiotonic Agents; D004095:Dihydropyridines; D010726:Phosphodiesterase Inhibitors; D011724:Pyridazines; C115124:Sch 00013