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(Circulation. 1995;91:1560-1567.)
© 1995 American Heart Association, Inc.

Articles

Effect of ß-Adrenergic Receptor Blockade on Blood Flow to Collateral-Dependent Myocardium During Exercise

Jay H. Traverse, MD; John D. Altman, MD; James Kinn, MD; Dirk J. Duncker, PhD, MD; Robert J. Bache, MD

From the Cardiovascular Division, Department of Medicine, University of Minnesota Medical School, Minneapolis.

Correspondence to Robert J. Bache, MD, Cardiovascular Division, Department of Medicine, University of Minnesota Medical School, Box 508 UMHC, 420 Delaware St SE, Minneapolis, MN 55455.

Background ß-Adrenergic receptors have been identified in isolated coronary collateral blood vessels, but their functional significance in the intact heart has not been demonstrated.

Methods and Results We measured myocardial blood flow with radioactive microspheres in normal and collateral-dependent myocardium in eight dogs trained to run on a treadmill before and after ß-adrenergic blockade with propranolol, 200 µg/kg, a dose that effectively inhibited the increase in coronary blood flow produced by selective ß₁- and ß₂-adrenergic agonists. Collateral vessel growth was stimulated with 2-minute intermittent occlusions of the left anterior descending artery followed by permanent occlusion. During control exercise, blood flow in the collateral zone was 38±5% less than in the normal zone. At identical levels of exercise, with heart rate maintained constant by atrial pacing, propranolol decreased mean blood flow in the collateralized myocardium from 1.93±0.17 to 1.50±0.14 mL · min^-1 · g^-1 (P<.01), while increasing the subendocardial to subepicardial blood flow ratio from 0.78±0.11 to 0.91±0.10 (P<.05). The decrease in collateral zone blood flow in response to propranolol resulted from an increase in both transcollateral resistance from 25.9±2.3 to 35.2±4.3 mm Hg · mL^-1 · min · g (P<.05) and small-vessel resistance in the collateral-dependent myocardium from 30.9±4.7 to 44.0±8.8 mm Hg · mL^-1 · min · g (P<.07). Blood flow to the normal zone was also significantly reduced from 3.14±0.21 to 2.23±0.12 mL · min^-1 · g^-1 (P<.01) after propranolol.

Conclusions ß-Adrenergic blockade decreased blood flow to collateral-dependent myocardium during exercise. These results indicate that ß-adrenergic receptor activation contributes to vasodilation of coronary collateral vessels during exercise.

Key Words: microspheres • occlusions • blood flow

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