Intracoronary alpha 2-adrenergic receptor blockade attenuates ischemia in conscious dogs during exercise.
Studies on the role of alpha-adrenergic constrictor tone in the coronary vascular bed during ischemia were performed in dogs running on a treadmill. The animals were instrumented with a left ventricular pressure transducer, and regional systolic wall thickening (%WTh) was assessed by sonomicrometry in the anterior and posterior walls of the left ventricle. An intracoronary catheter was implanted chronically in the circumflex coronary artery, and a hydraulic cuff was placed proximally around the artery. After beta-adrenergic blockade with propranolol (0.8 mg/kg i.v.), acute stenosis of the coronary artery was performed during running in five dogs to induce severe regional myocardial dysfunction in the posterior wall. Intracoronary infusion of the selective alpha 2-adrenergic blocking agent idazoxan (80 micrograms/kg) improved %WTh in the ischemic region from 5.1 +/- 1.6 to 10.8 +/- 2.8% (p less than 0.05), without any significant effect on the anterior wall. Blood flow to the subendocardium of the posterior wall (radioactive microspheres) increased from 0.17 +/- 0.05 to 0.45 +/- 0.30 (ml/min)/g (p less than 0.05). It is concluded that in exercising dogs subjected to beta-adrenergic blockade, significant postjunctional alpha 2-adrenergic receptor-mediated coronary vasoconstriction exists, even during severe ischemia. Regional alpha 2-adrenergic receptor blockade can reduce regional ischemia and improve contractile function by attenuating exercise-induced sympathetic vasoconstriction in this conscious animal model.
D000317:Adrenergic alpha-Antagonists / Q000627:therapeutic use*; D000818:Animals; D003243:Consciousness; D003326:Coronary Circulation; D003327:Coronary Disease / Q000188:drug therapy*; D003331:Coronary Vessels / Q000294:innervation*; D004146:Dioxanes / Q000627:therapeutic use*; D004147:Dioxins / Q000627:therapeutic use*; D004285:Dogs; D019329:Idazoxan; D009200:Myocardial Contraction; D005082:Physical Exertion; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D014661:Vasoconstriction
D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D004147:Dioxins; D011942:Receptors, Adrenergic, alpha; D019329:Idazoxan