title: Differential inhibitory action of phorbol-12,13-dibutyrate on the positive inotropic effect of endothelin-1 and Bay K 8644 in the isolated rabbit papillary muscle.
abstract: Endothelin-1 (ET-1) elicited a concentration-dependent positive inotropic effect on the rabbit isolated papillary muscle (electrically driven at 1 Hz at 37 degrees C). The duration of isometric contractions was prolonged by ET-1 in a concentration-dependent manner mainly by prolongation of relaxation time. A tumor-promoting phorbol ester, i.e., phorbol-12,13-dibutyrate (PDBu), inhibited selectively the positive inotropic effect of ET-1 at the concentration that it did not (10 nmol/L) or only slightly (10-20% at 100 nmol/L) reduced the basal force of contraction and the positive inotropic effect of Bay K 8644. The positive inotropic effect of 10 mumol/L of phenylephrine mediated via myocardial alpha 1-adrenoceptors (in the presence of 0.3 mumol/L of bupranolol) was likewise inhibited by PDBu in the same concentration range as it suppressed the ET-1-induced positive inotropic effect. PDBu at concentrations higher than 100 nmol/L inhibited the positive inotropic effects of Bay K 8644 and isoproterenol, and decreased the basal force of contraction in a concentration-dependent manner to a similar extent. Thus, PDBu exhibited selective and potent inhibitory action on the ET-1-induced and alpha 1-adrenoceptor-mediated positive inotropic effect (compared with that on the effect of the Ca2+ channel agonist Bay K 8644 and a beta-adrenoceptor agonist). The present findings indicate that ET-1 elicits a positive inotropic effect on the rabbit ventricular myocardium, the characteristics of which are similar to those of myocardial alpha-adrenoceptor activation, which may involve the phosphoinositide hydrolysis.
authors.affiliation: Department of Pharmacology, Yamagata University School of Medicine, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Endoh
authors.forename: M
authors.initials: M
authors.lastname: Takanashi
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D000818:Animals; D004558:Electric Stimulation; D016232:Endothelins / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D010210:Papillary Muscles / Q000187:drug effects*; D010656:Phenylephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011817:Rabbits; D015398:Signal Transduction / Q000187:drug effects; D013268:Stimulation, Chemical
chemical_list: D016232:Endothelins; D010656:Phenylephrine; D015240:Phorbol 12,13-Dibutyrate; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D007545:Isoproterenol