title: Alpha 1-adrenergic receptor responses in alpha 1AB-AR knockout mouse hearts suggest the presence of alpha 1D-AR.
abstract: Two functional alpha(1)-adrenergic receptor (AR) subtypes (alpha(1A) and alpha(1B)) have been identified in the mouse heart. However, it is unclear whether the third known subtype, alpha(1D)-AR, is also present. To investigate this, we determined whether there were alpha(1)-AR responses in hearts from a novel mouse model lacking alpha(1A)- and alpha(1B)-ARs (double knockout) (ABKO). In Langendorff-perfused hearts, alpha(1)-ARs were stimulated with phenylephrine. For ABKO hearts, phenylephrine reduced left ventricular pressure and coronary flow (to 87 +/- 2% and 86 +/- 4% of initial, respectively, n = 11, P < 0.01). These effects were blocked by prazosin and 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]-8-azaspirol[4,5]decane-7,9-dione] dihydrochloride, suggesting that alpha(1D)-AR-mediated responses were present. In contrast, right ventricular trabeculae from ABKO hearts did not respond to phenylephrine, suggesting that in ABKO perfused hearts, the effects of phenylephrine were not mediated by direct actions on cardiomyocytes. A novel finding was that alpha(1)-AR stimulation caused positive inotropy in the wild-type mouse heart, in contrast to negative inotropy observed in mouse cardiac muscle strips. We conclude that mouse hearts lacking alpha(1A)- and alpha(1B)-ARs retain functional alpha(1)-AR responses involving decreases of coronary flow and ventricular pressure that reflect alpha(1D)-AR-mediated vasoconstriction. Furthermore, alpha(1)-AR inotropic responses depend critically on the experimental conditions.
authors.affiliation: Department of Medicine and Cardiovascular Research Institute, University of California and Veterans Affairs Medical Center, San Francisco, USA.
authors.forename: Lynne
authors.initials: L
authors.lastname: Turnbull
authors.forename: Diana T
authors.initials: DT
authors.lastname: McCloskey
authors.forename: Timothy D
authors.initials: TD
authors.lastname: O'Connell
authors.forename: Paul C
authors.initials: PC
authors.lastname: Simpson
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Baker
mesh_terms: D058668:Adrenergic alpha-1 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D003326:Coronary Circulation / Q000187:drug effects; D003971:Diastole; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D009200:Myocardial Contraction / Q000187:drug effects; D010656:Phenylephrine / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D018340:Receptors, Adrenergic, alpha-1 / Q000172:deficiency* / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology; D016277:Ventricular Function, Left
chemical_list: C547714:Adra1a protein, mouse; C547717:Adra1b protein, mouse; C547720:Adra1d protein, mouse; D058668:Adrenergic alpha-1 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D010879:Piperazines; D018340:Receptors, Adrenergic, alpha-1; D010656:Phenylephrine; C053428:BMY 7378