title: Coronary alpha-adrenergic tone and contraction of ischemic myocardium in awake dog.
abstract: The effect of neurogenic coronary vasomotor tone upon contraction in ischemic myocardium was investigated in awake, mongrel dogs. The animals were chronically instrumented with a hydraulic occluder around the left circumflex coronary artery; a small catheter was also implanted within the vessel. Ultra-sound crystal pairs were placed distal to the occluder in myocardium perfused by the left circumflex artery. Pacing electrodes were sutured onto the right ventricular conus. During the experiment (n = 6) the occluder was inflated to stenose the vessel; the imposition of cardiac pacing (210/min) in conjunction with this stenosis resulted in depressed contraction of the myocardium distal to the occluder as assessed by the ultra-sound crystals: Segmental shortening decreased to 45.4 +/- 5.4% of unpaced control. Phentolamine, an alpha-antagonist, was then infused into the left circumflex catheter for ten minutes (0.1 mg/min) and the experiment repeated. After the alpha-blockade the combination of coronary stenosis and heart rate pacing decreased segmental shortening to only 84.6 +/- 10.1% of control, which was significantly (P less than 0.01) improved relative to the unblocked condition. In another experiment (n = 4), a less severe stenosis was imposed upon the left circumflex vessel. During pacing, muscle shortening decreased to 94 +/- 8.5% of control. Infusion of phenylephrine, an alpha-agonist, for ten minutes (0.1 mg/min) resulted in a 56.7 +/- 5.9% decrease in shortening during pacing; this was significantly greater (P less than 0.01) than the previous decrease. These data indicate that coronary alpha-adrenergic tone can significantly compromise regional myocardial function even in ischemic muscle whose coronary blood flow reserve has been exhausted.
authors.affiliation: Department of Physiology and Biophysics, University of Kentucky College of Medicine, Lexington 40536-0084.
authors.forename: S R
authors.initials: SR
authors.lastname: Vallance
authors.forename: D C
authors.initials: DC
authors.lastname: Randall
authors.forename: J D
authors.initials: JD
authors.lastname: Yingling
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002304:Cardiac Pacing, Artificial; D003243:Consciousness; D003326:Coronary Circulation / Q000187:drug effects / Q000502:physiology; D003327:Coronary Disease / Q000503:physiopathology*; D004285:Dogs; D005260:Female; D006321:Heart / Q000294:innervation* / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D010646:Phentolamine / Q000494:pharmacology*; D010656:Phenylephrine / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology*
chemical_list: D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D010646:Phentolamine