Abstract
This study was carried out to test the hypothesis that adrenergic coronary vasoconstriction limits blood flow to hypoperfused regions of myocardium during exercise. The vasoconstrictor influence of α-adrenergic receptor subtypes was assessed by use of selective adrenergic blocking agents. Dogs chronically instrumented with a circumflex coronary artery hydraulic occluder and an intra-arterial catheter underwent treadmill exercise in the presence of a coronary stenosis that decreased distal perfusion pressure to 40 mm Hg. Myocardial blood flow was measured with radioactive microspheres (15 μm) before and during selective α1- or α2-adrenergic receptor blockade produced by intracoronary infusion of prazosin (1 μg/kg/min x 10 min) or idazoxan (1 μg/kg/min x 10 min), respectively. Coronary perfusion pressure was held equal before and during receptor blockade with the hydraulic occluder. Compared with control exercise, subendocardial blood flow increased during α1-receptor blockade with prazosin from 0.60 ± 0.14 to 1.12 ± 0.17 ml/min/g p < 0.05), and mean transmural flow increased from 1.07 ± 0.19 to 1.60 ± 0.22 ml/min/g (p < 0.05). In contrast, subendocardial and mean transmural blood flow were not different from control during selective α2-adrenergic receptor blockade with idazoxan (0.48 ± 0.10 vs. 0.67 ± 0.14 ml/min/g, p = 0.33, and 0.82 ± 0.15 vs. 1.02 ± 0.20 ml/min/g, p = 0.45, respectively). These data indicate that even in the presence of a coronary stenosis that causes substantial myocardial underperfusion during exercise, residual coronary vasoconstrictor tone is present in ischemic myocardium, and this vasoconstriction is mediated predominantly by the α1-adrenergic receptor.
Original language | English (US) |
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Pages (from-to) | 1688-1697 |
Number of pages | 10 |
Journal | Circulation research |
Volume | 65 |
Issue number | 6 |
DOIs | |
State | Published - 1989 |
Keywords
- coronary circulation
- idazoxan
- myocardial ischemia
- prazosin
- α-adrenergic receptors