Effect of alpha 1-adrenergic blockade on myocardial blood flow during exercise after myocardial infarction.
The effect of alpha 1-adrenergic blockade with prazosin on myocardial blood flow at rest and during two levels of treadmill exercise was assessed in 16 chronically instrumented dogs 9-14 days after myocardial infarction had been produced by occlusion of the left circumflex coronary artery. During resting conditions prazosin did not alter mean myocardial blood flow or the subendocardial-to-subepicardial flow ratio in either normally perfused or collateral-dependent myocardium. However, during exercise at comparable external work loads and comparable rate-pressure products, prazosin significantly increased blood flow to normally perfused (27% increase at the second level of exercise, P less than 0.001) and collateral-dependent myocardium (35% increase at the second level of exercise, P less than 0.001) compared with control. In addition, prazosin caused a small but significant decrease in the subendocardial-to-subepicardial flow ratio in both normal (1.27 +/- 0.04 to 1.19 +/- 0.04; P less than 0.01) and collateral-dependent myocardium (0.57 +/- 0.11 to 0.52 +/- 0.11; P less than 0.01) compared with control, reflecting a disproportionally greater increase in subepicardial flow in response to alpha 1-adrenergic blockade. These data demonstrate that alpha 1-adrenergic vasoconstriction inhibits coronary vasodilation during exercise, even in areas of collateral-dependent myocardium relatively early after coronary artery occlusion.
Herzog
C A
CA
Department of Medicine, University of Minnesota Medical School, Minneapolis 55455.
Dai
X Z
XZ
Bache
R J
RJ
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects*; D004285:Dogs; D005260:Female; D006439:Hemodynamics; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009203:Myocardial Infarction / Q000473:pathology / Q000503:physiopathology*; D011224:Prazosin / Q000494:pharmacology*
D000317:Adrenergic alpha-Antagonists; D011224:Prazosin