title: Myocardial alpha 1A-adrenoceptor subtypes in rabbit: differentiation by a selective antagonist, HV723.
abstract: The influence of a newly developed alpha 1-adrenoceptor antagonist, HV723 (alpha-ethyl-3,4,5-trimethoxy-alpha-(3-((2-(2-methoxy-phenoxy)ethyl)-ami no)- propyl) benzeneacetonitrile fumarate), on the positive inotropic effect and acceleration of phosphoinositide hydrolysis induced by phenylephrine via alpha 1-adrenoceptors in the presence of bupranolol (0.3 microM) was studied in the rabbit ventricular muscle: (1) HV723 at low concentrations (1-100 pM) attenuated the maximal inotropic response by 15-20% without altering the pD2 value for and [3H]inositol monophosphate accumulation induced by phenylephrine. The inhibitory action of HV723 (1-100 pM) showed a close resemblance to that of a selective alpha 1A antagonist, (+)-niguldipine. (2) HV723 (> or = 1 nM) shifted the concentration-response curve for phenylephrine to the right and downwards in association with a partial inhibition (42.5%) of [3H]inositol monophosphate accumulation. The IC50 values of HV723 for the inhibition of the inotropic response and phosphoinositide hydrolysis were approximately equal to the Kilow value determined by displacement of [3H]prazosin-specific binding. The mode of the inhibitory action of HV723 (> or = 1 nM) resembled that of another alpha 1A antagonist, WB 4101. These results indicate that HV723 shows a differential antagonistic action on the alpha 1A-mediated responses depending on the concentration: HV723 (1-100 pM) selectively inhibits the (+)-niguldipine-sensitive subclass to lead to a decrease in the maximal inotropic response with no change in phosphoinositide hydrolysis; HV723 (> or = 1 nM) may antagonize the WB 4101-sensitive subtype coupled to acceleration of phosphoinositide hydrolysis.
authors.affiliation: Department of Pharmacology, Yamagata University School of Medicine, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kohi
authors.forename: H T
authors.initials: HT
authors.lastname: Yang
authors.forename: M
authors.initials: M
authors.lastname: Endoh
mesh_terms: D000097:Acetonitriles / Q000378:metabolism / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive; D002046:Bupranolol / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004095:Dihydropyridines / Q000494:pharmacology; D006352:Heart Ventricles; D006868:Hydrolysis; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000378:metabolism; D010656:Phenylephrine / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D011224:Prazosin / Q000378:metabolism; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000097:Acetonitriles; D000317:Adrenergic alpha-Antagonists; D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D010716:Phosphatidylinositols; D011942:Receptors, Adrenergic, alpha; C058562:HV 723; D010656:Phenylephrine; D002046:Bupranolol; D011224:Prazosin; C054074:niguldipine