Intracoronary infusion of the alpha 2-adrenergic blocker idazoxan improved regional systolic wall thickening in the ischemic region from 5.1% to 10.8% (p<0.05) in exercising dogs.
Does intracoronary alpha 2-adrenergic receptor blockade with idazoxan improve regional systolic wall thickening and blood flow in conscious dogs with acute coronary stenosis during exercise?
In a canine model, regional alpha 2-adrenergic receptor blockade with idazoxan reduces ischemia and improves contractile function by attenuating exercise-induced sympathetic vasoconstriction.
Absolute Event Rate: 10.8% vs 5.1%
p-value: p=<0.05
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.
Seitelberger et al. (Tue,) conducted a other in Myocardial ischemia (n=5). Idazoxan (selective alpha 2-adrenergic blocking agent) vs. Baseline (ischemia before infusion) was evaluated on Regional systolic wall thickening (%WTh) in the ischemic region (p=<0.05). Intracoronary infusion of the alpha 2-adrenergic blocker idazoxan improved regional systolic wall thickening in the ischemic region from 5.1% to 10.8% (p<0.05) in exercising dogs.
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